Extended Speaker Abstracts1
ADDRESSING MULTIPLE STRESSES
Eric J. Barron
The University of Texas at Austin
The nature of the environmental issues facing any nation demands a capability that allows us to enhance economic vitality, maintain environmental quality, limit threats to life and property, and strengthen fundamental understanding of the earth. In each case it is the ability to anticipate the future (e.g., a forecast of an impending storm, a prediction of the water quality change in response to a new source of pollutant) that makes information about the earth system truly useful. Reliable information about the future (i.e., predictions) is the key to addressing environmental issues. However, society requires greater access to and greater confidence in both information and forecasts or projections in order to weigh the advantages and risks of alternative courses of action by private and public decision makers. Such information is a key commodity in enhancing economic vitality and societal well-being. What stands in our way of providing this information?
THE NATURE OF THE PROBLEM
The driving forces that alter environmental quality and integrity are widely recognized, involving primarily weather and climate, patterns of land use and
land cover, and resource use with its associated waste products. But a key feature of most regions is that more than one driving force is changing simultaneously. Consequently, most locations are characterized by multiple stresses. The effect of a combination of environmental stresses is seldom simply additive. Rather, they often produce amplified or damped responses, unexpected responses, or threshold responses in environmental systems. Multiple, cumulative, and interactive stresses are clearly the most difficult to understand and hence the most difficult to manage.
In contrast, most research, analysis, and policy are based on studies that examine discrete parts of these complex problems. Basically, earth and environmental sciences tend to focus on cause and effect, where we seek to understand how a specific element of the system may respond to a specific change or perturbation (e.g., acid rain on lake fisheries). The lack of an ability to assess the response of the system to multiple stresses limits our ability to assess the impacts of specific human perturbations, to assess advantages and risks, and to enhance economic and societal well-being in the context of global, national, and regional stewardship.
However, the problem is not limited simply to moving from analysis of discrete parts of complex problems to a more comprehensive analysis.
First, economic vitality and societal well-being are increasingly dependent on combining global, regional, and local perspectives. A “place-based” imperative for environmental research stems from the importance of human activities on local and regional scales, the importance of multiple stresses on specific environments, and the nature of the spatial and temporal linkages between physical, biological, chemical, and human systems. We find the strongest intersection between human activity, environmental stresses, earth system interactions and human decision making in regional analysis coupled to larger spatial scales.
Second, a decade of research on greenhouse gas emissions, ozone depletion, and deforestation has clarified many critical unanswered questions. However, the last decade of effort has also revealed a number of challenges, most notably the challenge of creating integrated global observational capabilities and the computational and scientific limitations inherent in creating a truly integrated, global, coupled system modeling capability suitable for assessing impacts and adaptations. These problems are noteworthy in global change science, but they become intractable at the scales of human decision making. A major part of the problem is simply a matter of scale combined with the sheer information required to combine physical, biological, chemical, and human systems if the framework is global. For example, whereas a global integrated observing system is challenging but tractable and plays a fundamental role on the scale of a global circulation model, it collapses under its own weight at higher spatial resolutions if we demand a truly comprehensive data system involving the host of observations spanning biology, hydrology, soils, weather, etc., required to address problems at
the scales of human decision making. For this reason, we have never fully realized the objective of “earth system science.”
Recognition of the importance of developing a more integrated approach to environmental research was abundantly clear in the U.S. National Assessment of Climate Change Impacts on the United States (NAST, 2000). The first recommendation for future research focused on developing a more integrated approach to examining impacts and vulnerabilities to multiple stresses. There were many examples in which the key limitation to the assessment of potential impacts to climate change was a lack of knowledge of other stressors. For example, changes in insect-, tick-, and rodent-borne diseases could be clearly tied to weather and climate, but a number of other environmental factors that could influence the disease vectors (e.g., the importance of land cover/land use on disease hosts), transmission dynamics, and population vulnerabilities severely limited our ability to make robust conclusions on how climate change might influence the distribution and occurrence of many infectious diseases in the future.
ADDRESSING SOCIETAL NEEDS
The need for society to enhance economic vitality, while maintaining environmental quality and limiting threats to property and life, should drive the environmental research and operational enterprise. These societal needs lead to a vision that requires a focus on multiple stresses. To address this vision, we need to develop a comprehensive regional framework for environmental science. This vision includes five elements:
an integrated regional web of sensors, including physical, chemical, biological, and socioeconomic factors, that link existing observations into a coherent framework and enable new observations to be developed within an overall structure;
an integrated and comprehensive regional information system, accessible to a wide variety of researchers, operational systems, and stakeholders;
directed process studies designed to examine specific phenomena through field study to address deficiencies in understanding;
a regional, high-resolution modeling foundation for constructing increasingly complex coupled system models at the spatial and temporal scales appropriate for the examination of specific and integrated biological, hydrological, and socioeconomic systems; and
a strong connection to significant regional issues and stakeholders.
These five elements are described in detail below:
1. A Web of Integrated Sensors. The current U.S. observation strategy appears to be haphazard when viewed in the overall context of environmental
problems. The reason is clear. The observations are driven by different mission needs and tend to focus on the measurement of discrete variables at a specific set of locations designed to serve the different needs of weather forecasting, pollution monitoring, hydrological forecasting, or other objectives. The mission focus results in a diverse set of networks that are supported by a large number of different federal agencies, states, or regional governments. Increased awareness of a host of environmental issues drives demand for additional new observations. However, these new observations are frequently viewed independently of any overall structure or integrated observing strategy. Operational needs and research or long-term monitoring needs are also often independent. Importantly, regular and consistently repeated observations present added challenges in garnering sufficient financial resources. The end result is almost certainly fiscally inefficient, and undoubtedly limits our ability to integrate physical, biological, chemical, and human systems.
The limitations of the current observing strategy are widely recognized, and they have spurred efforts to develop global observing systems for global change, climate, and oceanic and terrestrial systems in the international arena. These efforts are commendable and must be encouraged, but they are also extremely challenging because of the breadth of measurements, nations, capabilities, and policies that are involved.
In contrast, at a regional level in the United States we have the potential to (a) link observing systems into a web of integrated sensors building upon existing weather and hydrological stations and remote sensing capability; (b) create the agreements across a set of more limited agencies and federal, state, and local governments needed to create a structure to the observing system; (c) provide a compelling framework that encourages or demands the integration of new observations into a broader strategy; and (d) create strong linkages between research and operational observations that result in mutual benefit. The result is likely to create new efficiencies through the development of measurement systems that are more comprehensive, rather than a suite of separately funded, disconnected systems. The result is also likely to result in greater scientific benefit to society and greater understanding due to the co-location or networking of many different measurement capabilities. The demonstration of fiscal efficiency and improved capability and resulting benefit are likely to create a significant additional impetus for developing national and global integrated observing systems.
2. Regional Information Systems. Society has amassed an enormous amount of data about the earth. New satellite systems and other observational capabilities promise enormous increases in the availability of earth data. Fortunately, technological innovations are allowing us to capture, process, and display this information in a manner that is multiresolution and four-dimensional. The major challenges involve data management; the storage, indexing, referencing, and retrieving of data; and the ability to combine, dissect, and query information. The
ability to navigate this information, seeking data that satisfy the direct needs of a variety of users, is likely to spark a new “age of information” that will promote economic benefit and engender new research directions and capabilities to integrate physical, biological, chemical, and human systems.
The efforts to create comprehensive information systems increasingly reflect federal and state mandates to make data more accessible and useful to the public and to ensure that our investments in research yield maximum societal benefit. The development of a global digital database is again an enormous challenge. In contrast, a regional or state focus becomes a logical test bed, enabling the participation of universities; federal, state, and local governments; and industry in the development of a regional information system that is tractable and for which immediate benefit for a state or region can be evident. Again, the demonstration of capability and resulting benefit are likely to create a significant additional impetus for developing national and global information systems.
3. Framework for Process Studies. Process studies are a critical element of scientific advancement because they are designed, through focused observations and modeling, to probe uncertainties in knowledge about how the earth system functions. In many cases mismatch between model predictions and observations can drive targeted investigations to limit the level of error. Frequently, efforts to couple different aspects of the earth system (e.g., the atmosphere and land-surface vegetation characteristics) prompt targeted exploration because the level of understanding is still rudimentary. The objective is to use field study to address deficiencies in our understanding. The benefit of these intensive studies is maximized when they can be coupled with a highly developed, integrated set of sensors, with readily accessible spatial and temporal data within a regional information system, and with a predictive model framework that readily enables the entrainment and testing of new information from process studies. Hence, a regional focus is empowered by process studies that are directly tied to answering specific questions designed to assess the impacts of specific human perturbations, to assess advantages and risks, and to enhance economic and societal well-being.
4. Predictive Capability. The value of reliable advanced information is widely recognized. For example, we have considerable experience with the benefit of reliable weather forecasts, whether it involves the planning of a day around a precipitation forecast, the protection of life and property that stems from severe weather warnings, or the economic benefit of weekly, seasonal, or interannual forecasts used by climate- or weather-sensitive industries such as agriculture, forestry, fisheries, construction, or transportation. For example, millions of dollars in commodity markets can be saved by regional utilities with advanced weather or seasonal forecasts, and El Niño forecasts a season in advance can substantially modify agricultural practice.
Prediction is central to the translation of knowledge about the earth system into economic benefit and societal well-being. Over the last several decades we have experienced enormous increases in our ability to forecast weather and to project climate and climate variability into the future. The demand for new forecasting products, involving air quality, energy demand, water quality and quantity, ultraviolet radiation, and human health indexes is also growing rapidly, and as we demonstrate feasibility and benefit, society is likely to demand a growing number of new operational forecast products on prediction timescales of days to decades into the future. Further, we already clearly sense that environmental issues will demand an even greater capability to integrate physical, biological, chemical, and human systems in order to develop the predictive capability needed to examine the response of critical regions or cases to multiple stresses.
Global weather and climate models provide the strongest physical foundation for more comprehensive predictive capability. The numerical models that underpin this type of forecast are increasingly becoming the framework for the addition of new numerical formulations designed to predict air quality, the water balance for river forecast models, and a host of other variables, including the migration of forests under climate change conditions. As we attempt to produce predictions at the scale of human endeavors, mesoscale models (capable of predicting synoptic weather systems) and downscaling of coarser resolution model output are increasingly becoming the focal point of weather and climate studies because of their potential to make predictions on the scale of river systems, cities, agriculture, and forestry. Enormous potential exists if we can institutionalize a mesoscale numerical prediction capability that meshes with regional sensor webs and information systems. Such a capability enables a strategy and implementation capability for building tractable coupled models, initiating experimental forecasts of new variables, assessing the outcomes associated with multiple stresses, and taking advantage of the discipline of the forecasting process to create a powerful regional prediction capability. This capability, built upon the numerical framework of weather and climate models, can be extended to air quality, water quantity and quality, ecosystem health, human health, agriculture, and a host of other areas.
It is time to bring a demanding level of discipline to the forecasting of a wide variety of environmental variables. The objective is to stimulate the interplay between improvements in observation, theory, and practice needed to develop capabilities of broad value to society. The discipline of forecasting is dependent on four steps: (1) collection and analysis of observations of present conditions; (2) use of subjective or quantitative methods to infer future conditions; (3) assessment of the accuracy of the prediction with observations; and (4) analysis of the results to determine how methods and models can be improved. At a minimum we are capable of bringing a much greater level of structure and discipline into our predictions of the future, ranging from specific forecasts to statistical ensembles
that include a measure of expected accuracy to an assessment of the range of possibilities.
5. Creation of a Vigorous and Continuous Link to Users and Decision Makers. We need to create a vigorous connection between the research and decision makers by (a) incorporating the variety of space and timescales and the diversity of variables that are important to decision makers; (b) emphasizing the education of the user in the meaning and significance of climate and land use information in order to promote greater use and more robust applications; (c) ensuring mutual information exchange and feedback; (d) focusing on communication and accessibility of information; (e) continuously evaluating and assessing the use and effectiveness of the services; (f) employing active mechanisms to enable the transition from research discovery to useful products; and (g) employing a variety of methods of education and outreach.
The above structure is inherently a hybrid between research and operational functions. Both benefit from the level of integration of observations and information, the targeted process studies, and the model development capability. An emphasis on a region-specific predictive capability will drive the development of new understanding and new suites of comprehensive interactive high-resolution models that focus on addressing societal needs. A key objective is to bring a demanding level of discipline to “forecasting” in a broad arena of environmental issues. Common objectives and an integrated framework will also engender new modes and avenues of research and catalyze the development of useful operational products. With demonstrated success, the concepts of integrated regional observation and information networks, combined with comprehensive models, will grow into a national capability that far exceeds current capabilities. Such a capability is designed to address a broad range of current and future regional and global environmental issues.
Eric Barron is dean of the Jackson School of the University of Texas at Austin. Prior to assuming his current position he served as dean of the College of Earth and Mineral Sciences and Distinguished Professor of Geosciences at the Pennsylvania State University. His research interests are in the areas of climatology, numerical modeling, and earth history. Dr. Barron received his Ph.D. in oceanography from the University of Miami.
DROUGHT: OBSERVATIONS, MECHANISMS, POTENTIAL SURPRISES AND CHALLENGES
University of Arizona
Drought is one of the most challenging and costly environmental concerns confronting society. Over time, many institutions have been developed to deal with drought, but there is still a regular multi-billion dollar annual drought impact in the United States alone. Moreover, a complete consideration of drought provides a sobering view of the future. The purpose of this presentation is to provide an overview of drought variability and related issues.
Drought is a concern worldwide, but by necessity this presentation will focus on North America only. Nonetheless, many of the North American lessons can inform climate-society debates elsewhere—particularly in Africa, where there is also a rich history of observations, as well as research on the causes and impacts of drought variability.
THE INSTRUMENTAL RECORD OF DROUGHT
Drought is always affecting some part of North America, and even a single-year drought has impact and is thus important. The longer droughts are of greater concern, with the droughts of the 1930s, 1950s, and 1999 to the present being the droughts of record and of most concern. These longer droughts all affected large portions of North America. The most recent drought is particularly notable in that it was hotter than the similar drought of the 1950s. In general, western North America has seen significant warming over the last 100 years, particularly in the last couple of decades.
It is notable that the recent period of unprecedented population increase in the western United States coincided with one of the wettest periods on record. It is also troubling that Colorado River water was divided up among basin states during the one of the other wettest periods: in total, 16.5 MAF of water was allocated per year, even though the measured flow during the early 20th century wet period was less than 15 MAF per year.
THE PALEOCLIMATIC RECORD OF DROUGHT
Even a quick glance at the paleoclimate record of drought makes it clear that the instrumental record provides a biased record of drought due to a shortness of record. Droughts comparable to the 1930s, 1950s or early 2000s have occurred,
in general, once or twice per century over the last 2,000 years. The true long-term average flow of the Colorado is well below what is allocated to western states and Mexico. All droughts of the 20th century were eclipsed by past droughts, both in terms of annual maximum severity, duration, and geographic extent. It is clear from the paleoclimatic record that droughts longer than a decade (i.e., “mega-droughts”) were not that rare and that droughts impacting much of the western United States have lasted as long as a century or more within the last 2,000 years. Paleoclimatic research has shown that at least one lake in the Sierra Nevada of western North America went dry for decades on more than one occasion—something that has not occurred since Europeans settled the West. The true range of “natural” drought variability is thus substantially larger and more complex than suggested by the last century of instrumental drought variation.
In general, most of the large droughts of the western United States have been large enough to affect more than one major river basin at a time, and some (e.g., the late 16th-century megadrought) apparently impacted the United States from coast to coast and from northern to southern borders. Many (all?) long-duration droughts moved spatially from year to year and usually included years with normal or above-normal rainfall.
Another key aspect of drought variability illuminated by the paleoclimatic record is that decades- to centuries-long hydrological “regimes” (e.g., characterized by rare/short or frequent/longer droughts) have begun and ended abruptly— transitions between drought regimes can take place over years to decades, whereas the regimes themselves can be significantly longer.
MECHANISMS OF DROUGHT VARIABILITY
Great strides have been made recently with respect to understanding the proximal cause of drought in North America. We have long known that drought in the southwestern United States (e.g., 1950s and the recent drought) have connections with ENSO and that dry winters are favored in La Niña years. More recently, modeling studies have confirmed that anomalous sea surface temperature (SST) patterns, particularly in the tropics, and particularly in the Indo-Pacific, can explain both 20th-century and earlier droughts. Moreover, research has now also identified strong relationships between decadal modes of Pacific and Atlantic variability with decadal patterns of wet and dry conditions over North America. Of course, the major challenge is to explain the causes of the anomalous—and persistent—ocean conditions that lead to North American drought.
Although land-surface feedbacks can play key roles in amplifying or damping drought, it appears that these feedbacks are not dominant in driving temporal drought variability. More work is needed on the role these feedbacks play, but only after recognizing that coupled atmosphere-ocean variability is likely more important.
It is just a matter of time until North America gets hit with a decadal mega-drought. This is likely regardless of how large any anthropogenic impact might be. Thus warned, why would anyone be surprised? This shortcoming of human nature needs to be understood and overcome.
ANTHROPOGENIC VERSUS NATURAL DROUGHT INFLUENCES
The IPCC (TAR and a recent CLIVAR-PAGES-IPCC workshop convened by Overpeck and Trenberth) concluded that anthropogenic forcing will likely increase the probability of drought in central and western North America. Exacerbating this likelihood is the fact that temperatures are already rising significantly in the West, and snowpack is already retreating in the same region (as a result of the warming). A lesson of the paleoclimatic record is that anthropogenic forcing could trigger an abrupt transition into a more drought-prone climatic regime, thus increasing the frequency and duration of drought. Given that these possibilities could materialize with or without significant future human-induced climate change, it makes sense to consider no-regrets strategies to reduce vulnerability to drought in either case.
Most recently it has been proposed that unprecedented warming in the tropical Indian and western Pacific Oceans—likely a result of global warming—is the cause of the ongoing western North American drought. This hypothesis is well supported by modeling studies and is troubling in that the anomalous warming could become the norm in the future in years without El Niño events. If dry conditions intensify this winter, it could be a sign that we are in what could turn out to be the first megadrought since Europeans settled North America.
CHALLENGES AND OPPORTUNITIES
Needless to say, there is a great deal of additional insight that could be revealed through a more comprehensive study of past drought and megadrought. Can we define the full range of possible drought sufficiently for successful no-regrets adaptation? What are the empirical links between drought and variability in sea surface temperatures? What sets up the anomalous SSTs? Are the anomalies forced or generated by internal variability in the coupled system? What are the potential triggers of abrupt hydrological change? Are there early warning signs to be monitored for? Can droughts and megadroughts be predicted? Are surprises avoidable?
Although the mechanisms of drought cannot be understood fully without much improved observations (particularly paleo), the most important challenge might be in the area of ocean and coupled atmosphere-ocean modeling. Whereas the instrumental record of drought can be simulated fairly well given specified (observed) SST fields, the same drought record cannot be simulated with state-
of-the-art coupled models. Clearly, the development of more realistic coupled models must be an urgent priority.
Dealing with drought requires the ability to understand regional climate variability over all seasons and to eventually be able to deliver reliable seasonal to interannual climate outlooks. At present, advances are limited by modeling regional-scale processes, and this limitation is in turn related by the lack of good regional-scale climate monitoring. Thus, there is an increased need for denser in situ climate observing in the topographically complex western epicenter for U.S. drought.
Even if we develop an ability to predict drought, we must work with stakeholders in society (particularly in central and western North America) to develop adaptation strategies that reduce vulnerability to megadrought. There is little doubt that such a drought will occur at some time in the future and that anthropogenic climate change will exacerbate the situation. There is also little doubt that stakeholders and institutions are ill prepared for the inevitable megadrought.
Jonathan Overpeck is both a professor and director of the Institute for the Study of Planet Earth at the University of Arizona. Dr. Overpeck’s research focuses on global and regional climate dynamics. His research aims to reconstruct and understand the full range of climate system variability, recognize and anticipate possible “surprise” behavior in the climate system, understand how the earth system responds to changes in climate forcing, and detect and attribute environmental change to various natural (e.g., volcanic, solar) and nonnatural (e.g., greenhouse gases or tropospheric aerosol) forcing mechanisms. His work also focuses on improving the use of climate knowledge by decision makers in society.
UNDERSTANDING HAZARD AND PREDICTABILITY OF DROUGHT
Kelly T. Redmond
Desert Research Institute
What are the regional differences in complexities of drought monitoring? What drought monitoring and data needs have been identified for the United States?
At first blush, drought seems like a simple concept. However, the many ways in which it is expressed show how complex a phenomenon it really can be. The following personal observations elaborate on this point.
THE DEFINITION OF DROUGHT
Over the years I have attended a large number of drought status meetings, and even if the subject is not discussed right away, sooner or later the conversation turns to a definition of drought. Many definitions are geared toward a specific economic sector, geographic province, or other situation. The definitions of drought attached to these situations are seldom general or readily generalizable, thus rather arbitrary, and thus not very satisfactory. There is a strong predilection to view drought almost solely in terms of its climatic and physical drivers. Most definitions refer to extended periods and to deficient precipitation. But what are the durations and amounts, and perhaps other attributes, that these are referenced to? And is there a single such referent?
It seems unavoidable that the context of the situation where the question is being posed has to be brought into play. And if context matters, then we are led to questions of “deficient from which standpoint?” Water deficiencies can occur when water income is not great enough, or when water outgo is too great. Some drought indices address a mismatch between supply and demand of water (e.g., the Palmer index family), typically in the soil, but a large number do not. Other measures, like the Standardized Precipitation Index (SPI), focus on supply, with the implication that this dominates. Technically, the SPI is not a drought index itself but rather one of many tools to evaluate drought. More generally, though, it seems that drought has come into existence when the amount of water available is not keeping up with expectations or needs. These expectations, in turn, are based on long-term expectations of supply balanced against long-term expectations of demand. What constitutes “long-term” has to do with the timescales for getting into or out of difficulty. These can of course vary quite widely, from hours to centuries, though we generally mean days to months or years, depending on the issue or sector.
A definition is not of much use if it is not always applicable. Nearly every concept of drought involves a water budget (water supply versus water demand)
that has somehow come to be “out of balance” over some extended time. For these reasons, I have been led toward a simpler and more widely applicable definition of drought:
insufficient water to meet needs.
The main point here is that both supplies and needs (demand) change, so that for a given rate of supply, if demand goes up, the likelihood of shortages arising from typical fluctuations in supply goes up. When Albuquerque’s population consisted of 19 people, the deficiency in supply that led to shortages was different from the deficiency in supply that resulted in shortages when there are 600,000 people. Both supply and demand are dynamic.
Furthermore, there are many demands for water from natural systems (vegetation and wildlife and fish), and any useful comprehensive definition of drought has to encompass all biological systems. We could add a clause that refers to the needs of such biological systems, but a simple definition is much more preferable from the standpoint of elegance and clarity of thought.
Even if supply is reduced, if there is still sufficient water to meet all needs, then there is no drought. If supply remains constant, and demand is increased, there can be drought where there was none before. Such imbalances in supply and demand express themselves as impacts. In essence, if there is no impact, there is no drought. Thus, an inescapable corollary that accompanies this line of reasoning is that
drought is defined by its impacts.
In routine assessment of drought, such as for the U.S. Drought Monitor, this is the approach commonly taken. This kind of definition is harder to deal with for those who like concrete, definite numbers, because it is “soft” and situation dependent. But I am unable to come up with any example of drought that is not situation dependent.
Expressing this somewhat differently, an adequate definition or framework for conceptualizing drought ought to work equally well in Death Valley and the Olympic Mountains, in Greenland or Kentucky or Panama or Kihei or Aconcagua. Biological systems in all those places must address water supply and demand.
REGIONAL DIFFERENCES IN THE CHARACTER OF DROUGHT
It is exactly the regional differences in how we view and describe drought that led to the foregoing train of thought. The nature of the lags in the physical system is of fundamental importance. These lags can be natural or human caused. When there are such lags (from storage mechanisms that depend on water phase—liquid or frozen—or from different types of buffering mechanisms—deep
aquifers, reservoirs, porous rock, etc.), generally a system of physical infrastructure, conventions, legal mechanisms, cultural and social practices, and the like will have grown up around them.
In the United States the most striking difference is of course the difference between snowmelt-driven systems and rain-driven systems. These are strongly tied to the seasonal variations in the timing of precipitation, and to temperature, since this influences the phase of new precipitation (liquid or frozen) and the melt and runoff characteristics. Temperature is very important for all of these processes and also affects the demand through the phenological stage. Though not often treated as such, temperature is a hydrological element. All of these factors are elevation dependent and can thus vary over quite small scales (less than a kilometer)—amount, seasonality, phase, vegetative demand, sublimation, and others. To cope with these factors, an elaborate system for tracking and managing water in the West has arisen, in part codified into law, and a large number of dams or other storage mechanisms have also arisen to retain water until it is needed. Furthermore, water flows downhill, so gravitational considerations are a necessity (storage upstream always has more flexibility). Also, somewhat separately, because of the mining heritage, a system of water rights has arisen in the West that is different from that in the East. These factors fold together in intricate and complicated (i.e., nonlinear) ways, with thus the potential for many kinds of interesting behavior.
Another regional factor is the distance between the supply of water and the demand for that same water, often hundreds of miles away, and many months, even years, afterward. The water that supplies desert cities typically arises in locations not even visible from those cities. This water crosses a variety of legal and political boundaries, necessitating a variety of agreements, compacts, and understandings. There are great differences regionally between rain-dominated and more humid environments such as in the eastern United States and the snow-dominated and very arid environments found in the western United States.
In addition there are significant differences among states and across international boundaries in how groundwater is addressed, particularly whether it is considered (legally) to be linked with surface water, even though it is very well known that physically this is the case. Recognizing and addressing this linkage could affect some key interest groups in ways that would not provide incentive to change.
Drought impacts are experienced across a continuum of spatial scales, many of them at the scale of an individual person or household or small business. We have much less information at those scales and often have none. This applies to the causative physical factors as well as to the individual impacts. If we are lacking these local impacts, we are not in a position to aggregate upward and identify impacts that are cumulatively large but individually small. In part this difficulty stems from the difficulty of sampling to this level. Such sampling takes time, resources, skilled personnel, and coordination so that other analogous results can
be compared and added. In general there are woefully few resources to address information needs at the local level. In addition, such capabilities vary widely from state to state; more uniformity is needed. This should be a priority of a national integrated approach to drought, such as with NIDIS (National Integrated Drought Information System). We are also lacking in mechanisms to record and track such information, but recent progress has been reported by the National Drought Mitigation Center in developing tools to assist with this cumbersome but important problem.
Until we can obtain comprehensive assessments of the full impacts of drought, across all scales, we cannot provide the documentation that decision makers often require to back up requests for utilization of public funds.
There are of course many factors at least as important as climate that govern whether there is enough water for a particular purpose. Trends in spatial distribution and numbers of people and population demographics greatly affect water use. There are many competing uses and needs for water by people (municipal and industrial, transportation, dilution and conveyance of waste, hydropower, recreation, traditional cultures) and by larger ecosystems (fish and wildlife, endangered species, silt deposition and delta health, benefits from flow fluctuation, marine and estuarine systems, delivery of fresh water affecting ocean circulation, nutrient transport and deposition). Water quantity and timing affect water quality. Each issue has optimal water flow and quality characteristics and requires that constraints be met for satisfactory function. These constraints cannot usually be both individually and collectively optimized simultaneously, thus requiring global optimization over all issues and thus compromises.
This is basically an issue of parts versus wholes. We can identify and describe each stress in great detail as a separate subject. It is when they combine that all sorts of interesting behaviors become possible. However, we should not lose sight of the fact that we deal with multiple stresses all the time and we generally make it through life anyway.
COMPLEXITY AND NONLINEAR DYNAMICS
Because we have multiple stresses interacting at the same time, and because these interactions are highly nonlinear, we are in effect automatically preregistered in a giant experimental game from which we cannot withdraw. Emergent phenomena abound, and we should not be surprised to see unexpected or unpredictable things occur. We cannot say in detail what those are going to be; it is rather simply an issue that we should be prepared to be surprised at any time.
Because of this, it seems that the intertwined subjects of complexity, nonlinear dynamics, and chaos (and allied concepts) have a great deal to say about the generalized behavior we would expect to encounter. One of my own difficulties has been to try to discern where the knowledge we have gained about this subject can be supplied in some useful, practical, specific, or otherwise helpful way. In other words, where are the “insertion points” for the knowledge and insights developed by this field, in trying to cope with drought in a multi-stress environment? As with the stock market (itself a highly complex and nonlinear phenomenon), “past performance may not be an adequate predictor of future performance.”
Many of our response mechanisms do not seem to adequately allow for low-probability, high-consequence phenomena that form part of the risk portfolio. What we really have is a large number of probability distributions (and some of them with heavy tails, such as precipitation) interacting in many ways, with nonzero odds of occasionally rather spectacular outcomes. By definition, we call these “surprises” but we should not be surprised (in a general way) to see (specific) surprises. We know they are likely to arise, but we do not know with any detail what they will consist of. The typical city fire department can be confident that a house will catch fire, but it cannot say which house. There are many military analogs, because in that arena many consequences of surprise are generally not favorable, but much thought and training are devoted to maintaining the flexibility to address them when they do happen.
Naturally we should try to anticipate as many types of outcomes from interacting stresses as possible, in a deterministic fashion, but it is simply hopeless to guess them all. Thus it is guaranteed that surprise will always be present.
All of this plays into our tendency to formulate management plans, and most especially, laws, that are unnecessarily (often in order to gain their approval) rigid and not reactive to new or developing information.
BOUNDARY CONDITIONS AND INITIAL CONDITIONS FOR DROUGHT
By boundary conditions I am referring to the general circumstances “external” to a particular water balance determination, analogous to a boundary value problem in mathematics. In truth, in a connected system, there is hardly anything that is really “external,” but that is being glossed over for now. As these conditions change, the degree or scope or other properties of some current drought situation are likely to be assessed differently. The history of how a current situation came into being may make a considerable difference as to what needs to be done, for two situations with similar current conditions.
One boundary condition that may not be stationary in time is demand, which is often proportional to population in some manner. A rather typical assumption made is that drought status is driven more by supply than demand. And it is true
that the relative (annual) variation of precipitation is typically two to five times larger than the relative variation of evapotranspiration. The temporal variation of demand is not zero, however. In addition, population growth, at whatever rate, can, for example, negate assumptions about the stasis of a system of interest.
Groundwater contamination, as one example, can drastically alter supply, even if the source of contamination has been slowly building or gathering. A contaminated plume that is many years old may show up all at once. Groundwater flow through fractured media can exhibit many properties of Levy diffusion and related “burst” behavior. The impacts of such behaviors are often regarded as “surprises” and thus as pathologies, whereas a more careful analysis would have allowed for their possible existence.
Certain climate conditions (prolonged drought or prolonged moisture) can tip a system into a new “basin of attraction” in terms of state variables. For example, slow withdrawal from a water table can suddenly kill plant life when the roots can no longer reach deep enough. Hysteresis can then occur, because the reverse trajectory is not possible (dead plants do not become undead when the roots are reached as the water table replenishes). Slow changes in demand can make it more likely that some extreme condition occurs more often than before, increasing the likelihood that simultaneous occurrence of multiple extreme conditions takes a system to coordinates in state space that it has not hitherto visited.
We are accustomed to the processes in various systems proceeding at certain ranges of rates. If sustainability is the goal, then there needs to be a matching of rates of supply versus demand, for all resources that are being consumed, or even merely used. In many cases groundwater withdrawal is occurring at far faster rates than the rates of aquifer recharge. This is especially true where we are mining groundwater that is hundreds or thousands of years old. Furthermore, recharge rates are highly variable and episodic in time (in various settings recharge can be steady or bursty), and in arid and mountainous environments especially, they are extremely variable in space, in both constant ways (mountains do not move, except in California) and time-dependent ways (monsoon thunderstorms, for example).
With systems that exhibit intermittent or bursty or transient behavior, the averaging time over which rates are computed can be very important. A heavy monsoon rainstorm in the desert may rain 5 inches per hour, but only for 10 minutes. The net effect of several such storms might later be expressed as “3 inches per year.”
In addition, another rate comes into play. This is the rate at which our perceptions change as the circumstances in our vicinity change. Nearly all human beings live more in the past than in the present; we are always behind in our thinking. In an ideal world we would probably actually be living in a projected
future (assuming we could do that correctly) and making our decisions from that perspective. But in reality our perceptions often lag the real situation because of learning times, communication delays, the need to spend time on other things, perhaps a certain unwillingness to be totally up to date, and the like. As an example, it seems likely that the typical native westerner is not fully aware of the full dimensions of sprawl in their favorite vicinity. Most of us are likely making decisions that reflect our understanding of how things were a minute or a week or a year ago, or two, or five, or 10, or 50. We probably could not cope if we endeavored to keep abreast of every development, so there may be elements of psychological defense mechanisms at work that have withstood the tests imposed by evolution.
The point here is that communication and the transmission of learning cannot occur instantly everywhere, every part of a system has imperfect knowledge of the status of the other parts, and the differences in such rates are a reflection of the contingent nature of history. These differences lead to differences in strategies for addressing whatever stresses are on the plate at the moment.
The order in which things occur makes a difference. We have heard this from a number of drought and water managers. A single wet year in a sequence of dry years can yield much different overall consequences than if that wet year had been first or last. In some systems the drought clock can be partially or fully reset by a well-timed recharge. To help create a “worst case” scenario, the study in the early 1990s of severe and sustained drought on the Colorado River initiated the dry period with the lowest observed runoff years in succession.
Furthermore, the sequencing of different facets of climate can have great consequences, such as a particular moisture regime (wet or dry) accompanied or followed by a particular temperature regime (hot or cold). Insects, pathogens, and other pests often show spectacular responses to such combinations. The mormon crickets that have been prevalent in the northern Great Basin in recent years are favored or hurt by specific sequences of weather and climate anomalies. Drought and warm temperatures are permitting bark beetle behavior on an unparalleled scale in the northern Rocky Mountains of the United States and Canada in the last few years. For the latter, threshold factors, such as the ability to squeeze in two generations per year instead of one, are one example where highly nonlinear processes can qualitatively change the manner in which a system works.
Political action on complex problems is very often affected by essentially random accidents of timing.
PREDICTABILITY AND PROBABILITY
With respect to the climate system, we have piecewise understanding of its internal workings, its current status, the status of boundary conditions, and the ability to model it to some level of accuracy. But all of these are imperfect. Some of these imperfections can be addressed through diligence and expenditure of resources, and others represent fundamental limitations inherent in what we can know. Predictions can be made better by improving the former, but are always subject to the limitations imposed by the latter. Prediction is only possible for patchy combinations of circumstances, and we can only know some of those combinations.
All of our understanding points to Nature as being fundamentally probabilistic. Thus, even though it is difficult, we should learn to work and think in this mode as much as we can. In particular, we should be thinking in terms of the probability distributions of our confidence in our observational database, and in the descriptions of how we model how the system evolves from one state to the next.
This represents a huge challenge for public education. In like manner, we have known about quantum mechanics for 80 years, but most of the public has a very poor understanding of this subject and does not even know it exists, even though it is the fundamental basis for how things function.
In atmospheric science, including both weather and climate forecasting, the ensemble approach has been increasingly applied and has resulted in better forecasts. This in effect constitutes a kind of poor man’s method for sampling the possible states of a system, given the observations and the understanding of some of their error characteristics, and for sampling the physical parameterizations that represent how certain processes work. The same set of equations is run many times over but with random differences imposed on the input data, reflecting observational uncertainty, and in more complex approaches (“superensembles”), averaging across models that have a variety of approaches to parameterization of some particular process. The outcome of a typical set of forecast runs is that there are many possible solutions, with tendencies to cluster in certain ways. There are methodologies that can arrive at a consensus forecast but still retain the uncertainty and that furnish confidence information of value to other parties trying to utilize these results.
This ensemble methodology seems particularly valuable whenever there are a large number of degrees of freedom in a system. The climate system certainly has this property, and the drought/impacts “system” has far more than that. Furthermore, many of the latter are not subject to physical parameterization and are thus probably better described by using probability distributions. This method seems to offer many possibilities beyond the world of meteorology and climate where it originated and is still being refined.
The goal is to obtain better knowledge of the probability distributions of possible outcomes and assess what level of risk is attached to each outcome in the
distribution. With this better understanding of what outcomes are possible, the costs and benefits associated with each outcome, and development of a weighted average outcome, can be evaluated. The net effect is that we do not end up making definitive and definite conclusions about what is or is not the case. We need to be neither too confident nor too diffident in what we believe, and we need probabilistic tools to help us with these assessments. Probabilities and risk-based approaches can lead to better decisions, including the tenacity with which we defend or suggest certain courses of action in the face of uncertain results.
The suggestion from this observer is that such approaches have the potential for reducing our usually undue confidence in the results we arrive at and the actions we recommend based on those results. This does not preclude the ability to utilize probabilistic guidance to help crystallize our thinking and make rapid, decisive, and definitive decisions when needed.
Some elements of this discussion were raised in the article “The Depiction of Drought: A Commentary,” by Kelly T. Redmond, Bulletin of American Meteorological Society, 2002, 83(8):1143–1147.
Kelly T. Redmond is regional climatologist and deputy director for the Western Regional Climate Center located at the Desert Research Institute in Reno, Nevada. His research and professional interests span every facet of western U.S. climate and climate behavior, its physical causes and behavior, how climate interacts with other human and natural processes, and how such information is acquired, used, communicated, and perceived. Dr. Redmond received his Ph.D. in meteorology from the University of Wisconsin, Madison.
DROUGHT MONITORING COMPLEXITIES IN THE WEST
U.S. Department of Agriculture
“What can be learned about the impacts and interactions of multiple stresses from records of western U.S. precipitation and climate observations and their relation to drought and water supply forecasting?”
“The future ain’t what it used to be.” Y. Berra
The western United States was built with, and is highly dependent on, water captured from mountain snowpacks that may be hundreds or even thousands of miles away from population centers and agriculture. The reservoirs built to meet the needs of agriculture, power generation, municipal water supply, and a variety of other uses were conceived, and in some cases built, nearly 100 years ago when populations were scarce, industry demand for power was in its infancy, and endangered species legislation did not exist.
The West’s climate and mystique have lured settlers for over 150 years; however, it is ironic that drought was the genesis of one of the largest migrations during the 1930s. The population of the West was only 11.9 million in 1930 but grew 15 percent to 13.7 million by 1940 during the drought years. The West was able to absorb this increase; however, a pattern of western migration had begun. Significant reservoir construction from 1930 to 1970 resulted in increased water availability and inexpensive power, allowing irrigated agriculture, increased populations, and industry to gain a secure foothold.
Between 1980 and 2000 the population of the West grew 47 percent, from 42.2 million to 62 million, with no significant increase in water storage infrastructure. By 2002 agriculture represented 25.5 million western acres, generating an annual products-sold market value of $51.1 billion.
Recent energy prices have ignited interest in nonfossil renewable energy generation. Agencies such as the Bonneville Power Administration, which markets power produced from 31 federal dams in the Columbia Basin, have established operating plans based on climate and streamflow records for the period 1929-1978. Climate variability, combined with a projected 8 percent increase in regional firm energy demands, from an estimated 23,300 average megawatts in 2005 to 25,200 average megawatts in 2012 will have a direct impact on power availability and western economies. Columbia Basin hydroelectric dams, which rely on winter snowpack accumulation and spring and summer melt cycles, provide 73 percent of the region’s energy (BPA, 2003).
RECENT TRENDS IN WESTERN U.S. STREAMFLOW VARIABILITY AND PERSISTENCE AND POTENTIAL IMPACTS ON DROUGHT
Forecast streamflows and reservoir rule curves govern daily, monthly, and water year reservoir operations for power generation, navigation, flood control, and endangered species management. Many rule curves were developed using data from the middle of the past century and may not fully represent the recent streamflow trends and variability. A recent publication in the Journal of Hydrometeorology, “A Recent Increase in Western U.S. Streamflow Variability and Persistence” (Pagano and Garen, 2005), investigated trends in western U.S. streamflow. Variability and persistence can combine to amplify stress in drought-prone areas or, in extreme cases, produce drought in previously drought-free areas.
From the abstract: “April-September streamflow volume data from 141 unregulated basins in the western United States were analyzed for trends in year-to-year variability and persistence. Decadal time-scale changes in streamflow variability and lag-1 year autocorrelation (persistence) were observed.
“The significance of the variability trends was tested using a jackknife procedure involving the random resampling of seasonal flows from the historical record. As shown in Figure 1, the 1930s-1950s was a period of low variability and high persistence, the 1950s-1970s was a period of low variability and anti-persistence, and the period after 1980 showed high variability and high persistence. In particular, regions from California and Nevada to southern Idaho, Utah, and Colorado have recently experienced an unprecedented sequence of consecutive wet years along with multiyear extreme droughts.
“These various streamflow characteristics are not necessarily varying on the same time scales or coincidentally; increases in variability have preceded increases in autocorrelation by approximately 5-10 years, which have in turn preceded increases in skewness by another five years. Nonetheless, the various phenomena have become ‘in phase,’ making the most recent 20 years the only part of the record that is highly variable, highly persistent, and highly skewed. This triple alignment is perhaps the most challenging scenario for water managers. One possible scenario involves a series of consecutive wet years that overwhelm reservoirs and inflate stakeholder expectations about the amount of water available. An extended stretch of dry years exhausts storage reservoirs and does not give them a chance to recover. Smaller reservoirs that do not have multiple-year storage capacity would be especially vulnerable. In comparison, individual dry years interspersed among wet years are tolerable.
“These decadal oscillations also have implications for water supply forecasting. Statistical streamflow forecasting techniques that use persisted spring and summer streamflow as a predictive variable for next year’s flows will lead the forecaster astray when the climate regime switches between positive and negative autocorrelation. The changes in persistence and variability are undoubtedly linked to changes in precipitation and temperature and not changes in basin char-
acteristics or soil properties. It is unknown at this time whether procedures that use antecedent autumn streamflow (e.g., September-November) as a predictive variable to index the effects of soil moisture are also vulnerable to this effect. The causes of the current triple alignment are unknown.”
SEASONALITY OF SNOWPACK AND DROUGHT IN THE WEST AND RECENT EVENTS
Recent publications by Mote (2005) highlight the shifts from traditional snow accumulation during the winter to a trend to warmer spring temperatures
and declines in springtime snow water equivalent (SWE) in much of the North American West over the period 1925-2000, especially since mid-century. The Pacific Northwest has experienced two years of extremely low snowpacks in the past five years, 2001 and 2005. The 2001 snowpack deficits resulted in the second-lowest Columbia Basin streamflow on record, and the 2005 snowpacks, while not as low as 2001 basin-wide, did set new records in the Cascades of Washington and Oregon. In contrast to 2001 and 2005, an above-average snow-pack on March 1 fell victim to record warmth and dryness over a two-month period (Pagano et al., 2004).
Warmer and wetter springs kick-start the growing season, and with potentially low snowpacks this can be problematic if water rights are called later in the growing season. The shift to earlier spring runoff in the West documented by Stewart et al. (2004) will pose challenges for water managers through the rest of this century.
After a six-year drought in the Great Basin, an enormous single-year snow-pack recharged soil moisture and resulted in significant spring runoff. Is this an aberration, or will a long-term drought reestablish itself in the region? Can a probability of occurrence be quantified for the next water year? Can rapid shifts in climate from abundance to drought be forecasted with reliability? What will convince users that this can be done?
DATA AVAILABILITY AND REQUIREMENTS FOR MONITORING DROUGHT, CLIMATE, AND WATER SUPPLY
The entire world has been transformed by the Internet. Within the last 20 years canary yellow teletype paper placed on a clipboard is now readily available for all to download and use. In the West, the SNOTEL data are downloaded several million times per year, giving customers the ability to develop and run site-specific or regional models to meet a wide variety of user needs beyond what can be done by traditional federal or state partners.
In addition to the Internet, affordable computers with spreadsheet and graphics software can replicate the work done in the past by mainframes.
Does a data gap really count if there is no need for the data (e.g., unpopulated areas, without agriculture)?
What is a temporal gap? How often should a station report to meet user needs? Does technology support frequent observations?
If data are poor, is that a data gap?
The SNOTEL dataset (~25 years) is a relatively new dataset compared to COOP network or paleo data, but it fills a very important vertical data void in the West. The oldest datasets (snow courses) are monthly or biweekly during the winter and extend back to the 1930s. Long-term snowpack records are a critical component of climate change research.
There is a critical need to provide quality control on all SNOTEL data. A project to provide quality control on SNOTEL temperature data will be completed in early 2006.
Remote monitoring is not cheap. SNOTEL sites require maintenance annually, or more often in some areas. A significant computer/communications investment is also necessary.
Plans to automate 900 manual snow courses with SNOTEL automation are in place and about a dozen snow courses or new sites/year are automated.
WATER SUPPLY FORECASTING
Statistically based methods are still in use and provide reasonable results given the calibration dataset. However, statistical methods do not handle late-season events (heavy spring rains) or early-season forecasts during October-December due to lack of snowpack.
Improvements are underway to do a better job of visualizing the data and incorporating new prediction techniques. In addition, simulation modeling can help distribute flows during critical/extreme hydroclimatic events. Simulation models may require more real-time middle- and lower-elevation stations to properly represent hydrological conditions. In any event, “clean datasets” are needed to calibrate either model.
There is also a need to integrate climate forecasts with hydrological models to account for climate variability. This will be a challenge since the user community needs to understand the relationship of uncertainty between the climate and hydrological forecasts.
In conclusion, increased climate and streamflow variability present an ever-growing challenge to those who live in the West. Increasing population and its affect on land use, the growing need for electricity, environmental concerns, and the silent stress of a potential long-term drought hover over the desk of every resource manager. Understanding and learning from recent climatic and hydrological experiences can and will prove valuable in this new century.
Mote, P., A. Hamlet, M. Clark, and D. Lettenmaier. 2005. Declining mountain snowpack in western North America. Bulletin of the American Meteorological Society 86(1):39-48.
BPA (Bonneville Power Authority). 2003. Pacific Northwest Loads and Resources Study—2003 White Book. (DOE/BP-3559).
Pagano, T., and D. Garen. 2005. A recent increase in western U.S. streamflow variability and persistence. Journal of Hydrometeorology 6(2):173-179.
Pagano, T., P. Pasteris, M. Dettinger, D. Cayan, and K. Redmond. 2004. Water Year 2004: Western water managers feel the heat. EOS, Transactions, American Geophysical Union, pp. 385-400.
Stewart, I., D. Cayan, and M. Dettinger. 2004. Changes in snowmelt runoff timing in western North America under a “business as usual” climate change scenario. Climate Change 62:217-232.
Philip Pasteris is a supervisory physical scientist at the National Water and Climate Service (NWCS) (in the Natural Resources Conservation Service [NRCS]) in Portland, Oregon, where he is responsible for the production and distribution of water supply forecasts for the western United States and management of the NRCS National Climate Program. Mr. Pasteris has also held positions as a supervisory meteorologist at NWCS and senior hydrologist at the Portland River Forecast Center for the National Weather Service (NOAA). He received his M.S. in meteorology from the University of Oklahoma.
MULTIPLE STRESSES AND CLIMATE VARIABILITY: WHAT IF THE NEXT KATRINA IS A DROUGHT?
William E. Easterling
Pennsylvania State University
The importance of social and environmental processes as preconditions for drought is well established. Such processes are often mentioned in standard definitions of drought. What is missing, however, is a whole human-environment system approach to defining, monitoring, and measuring the frequency and intensity of droughts that takes into account underlying meteorological, hydrological, ecological, and sociopolitical processes.
For purposes of discussion it is reasonable to assume that droughts are ultimately triggered by scarcity of expected natural water supply, whether by precipitation deficiency, change in timing of snowmelt, inadequate groundwater recharge, or other forms of water shortage caused by climate variability. Multiple stressors are environmental and social processes or events that combine to dictate the limits to which an organism/individual, household, ecosystem, community, or region can absorb water scarcity before incurring unacceptable environmental or social cost. Stressors that influence the emergence and intensity of droughts can usefully be categorized as primary, secondary, and tertiary. Primary stressors are factors that directly influence water supply or demand across a range of scales. They may be environmental, as in the case of land cover change that increases evapotranspiration, or social, as in the case of rapid population growth or growth of water-intensive industry. Secondary stressors create conditions that abet vulnerability to water shortage, such as rural depopulation, decreasing agricultural comparative advantage, or high dependence on river-borne transportation. Tertiary stressors inhibit resiliency or adaptive capacity with respect to water deficiency. They also may be either environmental, as in crop and ecological diversity, or social, as in availability of risk management institutions, such as insurance networks and contingency planning. Adequate assessment of drought potential must consider not only climatological factors but also the full suite of interacting primary, secondary, and tertiary stressors.
Although anything but a drought, Hurricane Katrina clearly demonstrates the importance of multiple stressors interacting with a strong meteorological event. Katrina was the perfect storm more because of how it combined with a remarkable set of multiple stressors than its pure thermodynamic energy. It was a Category 4 (out of 5) hurricane that struck a city that arguably could not have been constructed to be more in harm’s way. In addition to its elevation below sea level and the proven inadequacies of its levee and water pumping systems, the greater New Orleans region had become a critical port of entry for a significant percentage of the nation’s imports, including natural gas, oil, and subsequent refinery products. Much of the midwestern grain produced for export passes
through the port of New Orleans. This guaranteed that the impacts of Katrina would extend to the nation and the world. The large income divide separating New Orleans’ wealthy and poor citizens left a large impoverished population especially vulnerable to the storm and its aftermath simply because it lacked the means to evacuate. Moreover, the translation of scientific assessments of hurricane vulnerabilities into practical political decisions did not happen. The list of multiple stresses at work in New Orleans was large, and their synergism with themselves and the hurricane surely intensified the loss of life and property and propagated impacts well beyond the region hit by the storm. An interesting question to ask is, What if Katrina had been the drought equivalent of a Category 4 hurricane occurring throughout the Mississippi River Basin—a sort of Dust Bowl II? What would we want to know about processes of social and environmental change that exacerbate precipitation deficiency? To try to answer this question might shed light on what we know and what we do not know about how multiple stressors might interact with a severe drought and in the process point out important research gaps.
Precipitation averaged about 20 percent lower and temperatures about 1°C higher than current during the decade of the 1930s in the central and western Great Plains. Were such an event to recur today, there are a number of stressors that likely would amplify the environmental and societal impacts. (In fairness, there are also improvements in resiliency due to learning from previous droughts that might provide some protection from a recurrence of the Dust Bowl droughts.) Some of the key stressors that intensified the destruction and damage of Katrina, ironically, would intensify the hardship of a long, severe drought. Table 1 lists a few examples of environmental and social situations and changes that would almost be certain to intensify the impacts of a superdrought in the Mississippi River Basin (MRB). As pointed out below, the reliance of the MRB on primary commodities and their water-borne transport renders the region vulnerable to any kind of climatic fluctuation that disrupts.
I am not aware of research that has explored how trends in multiple stressors, such as those listed in Table 1, affect the frequency or intensity of droughts. The closest vein of research is exemplified by O’Brien et al. (2004), who examined the vulnerability of Indian agriculture to climate variability and a small set of global stressors to determine the effects of being “double exposed.” However, common sense suggests that rapid changes in one or more stressors that outstrip existing capacity to adapt to water shortage must, ipso facto, increase the frequency of dry events that become droughts. For example, the volume of barge traffic hauling corn down the Mississippi River to Louisiana for export increased at an annual average rate of 3.5 percent during the period 1972-1992. At the same time, the Pick-Sloan Missouri Basin Program calls for increasing water retention in the Missouri’s Upper Basin to meet hydroelectric and environmental needs, thus cutting flows to the Lower Basin and Mississippi River. This nonlinear increase in barge traffic combined with less flow from the Missouri River during dry spells
TABLE 1 Examples of Primary, Secondary, and Tertiary Stressors of Mississippi River Basin (MRB) Drought
suggests greater vulnerability of barge traffic, particularly in the lower MRB to once-minor low-flow events that now might constitute bona fide drought conditions. A recurrence of the 1930s droughts could be devastating to MRB agriculture, due to the direct impact on crop productivity and the diminished capacity to move grain to markets cheaply.
Multiple stresses must be accounted for in a comprehensive assessment of the potential frequency and magnitude of droughts. There are several research gaps that need to be addressed in this regard:
Improved understanding of how multiple stresses interact, both with themselves and climate variability, to influence vulnerability to water shortage;
Improved understanding of how adaptive capacity is influenced by multiple stresses;
Improved understanding of how multiple stresses and coping systems interact across different levels of scale (in space and time);
Using the understanding gained from 1, 2, and 3, whole human-environment analytical frameworks deployed with integrated assessment models, suites of leading indicators, and other comprehensive analytical methods are needed—the
USAID Famine Early Warning System (FEWS) could serve as a reasonable model;
Identification of coping system strengths (i.e., redundant response systems) and weaknesses (i.e., overburdened response systems); and
Stronger stakeholder involvement in whole human-environment system assessments to minimize exclusion of science-based risk analysis from applied risk management.
O’Brien, K. L., R. Leichenko, U. Kelkar, H. Venema, G. Aandahl, H. Tompkins, A. Javed, S. Bhadwal, S. Barg, L. Nygaard, and J. West. 2004. Mapping vulnerability to multiple stressors: Climate change and globalization in India. Global Environmental Change: Human and Policy Dimensions 14(4):303-313.
William E. Easterling is the director of the Penn State Institutes of the Environment and professor of geography with a courtesy appointment in agronomy at the Pennsylvania State University. Dr. Easterling’s research interests include the potential for agriculture in developed and developing countries to adapt to climate variability and change; the role of scale in understanding the vulnerability of complex systems; how land use change may influence the uptake and release of carbon in the terrestrial biosphere; the use of experimental long-term climate forecasts to assist decision making under conditions of uncertainty; and the development of methodologies for detecting the impacts of observed 20th-century climate change on natural and managed ecosystems. Dr. Easterling received his Ph.D. in geography from the University of North Carolina at Chapel Hill.
DROUGHT-INDUCED VEGETATION MORTALITY AND ASSOCIATED ECOSYSTEM RESPONSES: EXAMPLES FROM SEMIARID WOODLAND AND FORESTS
David D. Breshears
University of Arizona
Woody plant mosaics are a key attribute of ecosystems. A large portion of the terrestrial biosphere can be viewed as lying within a continuum of increasing coverage by woody plants (shrubs and trees), ranging from grasslands with no woody plants to forests with nearly complete closure and coverage by woody plants (Breshears and Barnes, 1999; Breshears, 2006). The characteristics of woody plants determine fundamental descriptors of vegetation types, including grassland, shrubland, savanna, woodland, and forest. Because woody plants fundamentally affect many key aspects of energy, water, and biogeochemical patterns and processes, changes in woody plant cover are of particular concern (Breshears, 2006).
Drought can cause rapid changes in vegetation by triggering woody plant mortality. Assessments of potential global change impacts initially focused on how vegetation types matched given climatic envelopes. Later focus turned to how vegetation patterns might migrate with changing climate, focusing on rates of plant establishment. More recently, the importance of drought-induced die-off of woody plants was highlighted as a major dynamic response to climate variation and change. In particular, ecotones have been noted as areas where changes in vegetation in response to climate ought to be most rapid and responsive, as highlighted by a case study of vegetation response to drought during the 1950s (Allen and Breshears, 1998). In response to a severe drought in the southwestern United States during the 1950s, ponderosa pine (Pinus pondersosa) trees at lower, drier sites died, resulting in a shift of the ponderosa pine forest/piñon-juniper woodland ecotone of more than 2 km in less than five years (Figure 1) and producing a rapid change in vegetation cover (Figure 2). Similarly, within the distributional range for piñon pine (Pinus edulis), many trees at lower, drier sites within also died.
Drought can trigger widespread tree mortality across a region. Although tree mortality almost certainly occurred across much of the Southwest in response to the 1950s drought (and probably for previous regional-scale droughts as well), few studies exist that allow scientists assessing impacts of drought to test predictions about the rapidity and extent of vegetation die-off response to drought. A recent drought beginning around the new millennium impacted the southwestern United States and was the most severe since that of the 1950s. Mortality of several species was observed throughout the Southwest. Mortality of piñon pine spanned
major portions of the species’ range, with substantial die-off occurring over at least 12,000 km2 (Breshears et al., 2005; Figure 3). For both droughts, die-off was related to bark beetle infestations, but the underlying cause of die-off appears to be water stress associated with the drought.
Drought-induced tree mortality might be exacerbated under higher temperatures. The recent drought in the southwestern United States that triggered regional-scale die-off of piñon pine across the Southwest was not as dry as the previous regional drought of the 1950s (Breshears et al., 2005; Figure 4). However, the recent drought was hotter than the 1950s drought by several metrics, including mean, maximum, minimum, and summer (June-July) mean temperature. Tree mortality in response to the recent drought appears to have been more severe than that of the previous drought. In addition to die-off occurring across the region, the limited available data suggest that extensive piñon pine mortality
occurred at upper-elevation wetter sites in response to the recent drought but not in response to the 1950s drought. Hence, the warmer temperatures associated with the recent drought may have produced more extensive tree die-off. Because global change is projected to yield droughts under warmer conditions—referred to as global-change-type drought—the die-off from the recent drought may be a harbinger of vegetation response to future global-change-type drought (Breshears et al., 2005).
Several other changes can accompany die-off of dominant overstory trees. In addition to the die-off of the dominant overstory tree species, other species underwent mortality in response to regional drought (Allen and Breshears, 1998; Breshears et al., 2005). These include juniper (Juniperus monosperma), a co-dominant with piñon pine for much of its range, and blue grama (Bouteloua gracilis), the dominant herbaceous species for many of these systems. Additionally, reductions in ground cover may contribute to an increase in erosion rates (Davenport et al., 1998; Wilcox et al., 2003). In particular, reductions in herbaceous ground cover might trigger a nonlinear increase in soil erosion once a threshold of herbaceous cover has been crossed. In addition, reductions in tree canopy cover can dramatically alter the distribution of near-ground energy (Martens et al., 2000). Therefore, die-off of overstory vegetation affects numerous key ecosystem processes that are dependent on incoming energy (Breshears, 2006).
Drought-induced fire also triggers rapid canopy change and high soil erosion rates. Drought patterns can also trigger larger-scale fire patterns (Swetnam and Betancourt, 1998). Crown fire within woodlands and forests also can cause large reductions in tree canopy cover. Additionally, soil erosion can increase dramatically following forest wildfire (Johansen et al., 2001). The combined impacts of fire and drought-induced tree mortality are highlighted by the major changes in woodland and forest vegetation that have occurred in northern New Mexico over the past 50 years (Breshears and Allen, 2002; Breshears et al., 2005). It will be at least several decades following one of these types of disturbances before reestablishment of similar tree canopy cover in semiarid woodlands and forests could occur.
Interactions among multiple effects of drought, including potential ecosystem cascades, remain major uncertainties requiring future research. Examples of drought-induced tree die-off in semiarid woodlands and forests highlight the rapidity and extensiveness with which drought can trigger vegetation change. Several nonlinear or threshold-like processes may occur and require improved prediction, including tree mortality, energy and water budget changes, and soil erosion thresholds. Systems can cascade through multiple states. For example, a location that had extensive ponderosa pine mortality in the 1950s had little reestablishment of ponderosa pine over the subsequent 50 years (Allen and
Breshears, 1998) and was within the region exhibiting extensive piñon pine mortality in 2002-2003 (Breshears et al., 2005); rates of soil erosion following the 1950s drought were and remain high. An ability to predict tree mortality, associated ecosystem responses, and effects on the carbon budget and on other ecosystem goods and services should be a high priority for future research (Breshears and Allen, 2002; Millennium Ecosystem Assessment, 2005).
Acknowledgments: I thank my coauthors on previous related publications for their insights on and contributions to concepts related to those presented here: C. D. Allen, N. S. Cobb, P. M. Rich, K. P. Price, R. G. Balice, W. H. Romme, J. H. Kastens, M. Lisa Floyd, J. Belnap, J. J. Anderson, O. B. Myers, C. W. Myers, B. P. Wilcox, S. N. Martens, F. J. Barnes, S. L. Ustin, H. C. Stimson and D. W. Davenport. Support was provided by Los Alamos National Laboratory and National Science Foundation (DIREnet:DEB-0443526 and SAHRA:EAR-9876800).
Allen, C. D., and D. D. Breshears. 1998. Drought-induced shift of a forest-woodland ecotone: Rapid landscape response to climate variation. Proceedings of the National Academy of Sciences U.S.A. 95:14839-14842.
Breshears, D. D. 2006. The grassland-forest continuum: Trends in ecosystem properties for woody plant mosaics? Frontiers in Ecology and the Environment 4:96-104.
Breshears, D. D., and F. J. Barnes. 1999. Interrelationships between plant functional types and soil moisture heterogeneity for semiarid landscapes within the grassland/forest continuum: A unified conceptual model. Landscape Ecology 14:465-478.
Breshears, D. D., and C. D. Allen. 2002. The importance of rapid, disturbance-induced losses in carbon management and sequestration. Ecological Sounding. Global Ecology and Biogeography 11:1-5.
Breshears, D. D., N. S. Cobb, P. M. Rich, K. P. Price, C. D. Allen, R. G. Balice, W. H. Romme, J. H. Kastens, M. L. Floyd, J. Belnap, J. J. Anderson, O. B. Myers, and C. W. Meyer. 2005. Regional vegetation die-off in response to global-change type drought. Proceedings of the National Academy of Sciences U.S.A. 102:15144-15148.
Collins, W. J., R. G. Derwent, C. E. Johnson, and D. S. Stevenson. 2002. The oxidation of organic compounds in the troposphere and their global warming potentials. Climatic Change 52:453-479.
Davenport, D. W., D. D. Breshears, B. P. Wilcox, and C. D. Allen. 1998. Sustainability of piñon-juniper woodlands—a unifying perspective of soil erosion thresholds. Viewpoint. Journal of Range Management 51:231-240.
Johansen, M. P., T. E. Hakonson, and D. D. Breshears. 2001. Post-fire runoff and erosion following rainfall simulation: Contrasting forests with shrublands and grasslands. Hydrological Processes 15:2953-2965.
Millennium Ecosystem Assessment. 2005. Ecosystems and human well-being: Synthesis reports. Washington, D.C.: Island Press.
Stimson, H. C., D. D. Breshears, S. L. Ustin, and S. C. Kefauver. 2005. Spectral sensing of foliar water conditions in two co-occurring conifer species: Pinus edulis and Juniperus monosperma. Remote Sensing of Environment 96:108-118.
Swetnam, T. W., and J. L. Betancourt. 1998. Mesoscale disturbance and ecological response to decadal climatic variability in the American Southwest. Journal of Climate 11:3128-3147.
Wilcox, B. P., D. D. Breshears, and C. D. Allen. 2003. Ecohydrology of a resource-conserving semi-arid woodland: effects of scale and disturbance. Ecological Monographs 73:223-239.
David D. Breshears is a professor at the University of Arizona in the School of Natural Resources and Ecosystem Sciences Theme Leader for the Institute for the Study of Planet Earth and has a joint appointment in the Department of Ecology and Evolutionary Biology. His research focuses on gradients of vegetation ranging from grassland through forest, vegetation dynamics, including drought-induced die-off, ecological-hydrological dynamics (ecohydrology), wind and water erosion, soil carbon measurement technology, and applications addressing land use, contaminant risks, and global change. He received his Ph.D. from Colorado State University.
UNDERSTANDING AND MANAGING MULTIPLE STRESSES IN THE CONTEXT OF A COMPLEX RIVER BASIN: THE COLORADO RIVER
Roger S. Pulwarty
WATERSHEDS, MULTIPLE STRESSES, AND STREAMS OF THOUGHT
Societies are always adapting incrementally and in diverse ways to a variety of integrated and cumulative changes. There is, however, little understanding of the long-term and widespread consequences of these adaptations at different levels of governance.
The “regional scale” has long been advocated as a useful organizational unit on which to coordinate and evaluate socially relevant research cognizant of geophysical, cultural, and jurisdictional boundaries. Yet attempts to manage consistent regional units of analysis, such as the watershed, have not met expectations. Difficulties arise in managing for particular outcomes given multiple contending perspectives and the uncertainties in variations and interactions between physical and ecological environments. The western United States offers and has offered unique opportunities for identifying lessons for strategic learning about the management of cross-scale environmental risks over time, particularly those associated with water. For example, droughts have played a major role in the evolution of western water institutions. Most notably, the droughts of 1865-1872 gave rise to prior appropriation law.
Gilbert White identified the major elements of integrated river basin development as follows: (1) multiple-purpose storage reservoirs, (2) basin-wide planning, and (3) comprehensive regional development. Studies of the first-order impacts of climate on each of these elements in the western United States indicate that vulnerability exists in the areas of storage and consumptive depletions versus renewable supply. Critical factors confronting sustainable resource use across western basins can be summarized under the following headings: population and consumption, water quality, environmental water allocation, uncertain reserved water rights, groundwater overdraft, outmoded institutions, aging urban water infrastructure, and evolving federal, state, and local relationships. Responses have included water banking, inter-basin transfers, advanced decision-support/expert systems, streamflow and demand forecasting, drought management programs, threshold indicators, and efficiency improvements.
The complications of changes in the spatial and temporal distribution of rainfall, soil moisture, runoff, frequency, and magnitudes of droughts and floods have not been explicitly included in response planning. Systems design, operational
inflexibility, and legal and institutional constraints also reduce the adaptability of water systems and confound most recommendations to date on responding to climate change. Potential water-resource-related focusing events across the western United States include
extreme and sustained climatic conditions (e.g., drought and floods);
large-scale inter-basin transfers;
quantification of tribal water rights;
an energy crisis;
changing transboundary responsibilities; and
regulatory mandates such as the Endangered Species and Clean Water acts.
Critical thresholds arise when buffers are diminished and/or response curves steepen. A conspicuous aspect of water resources management has been the lack of careful post-audits of the social and economic consequences of previous programs and projects in the context of background variability and change. Three kinds of assessment questions may be asked: (1) What is known about the effects of past development programs on the environment? (2) What are, and how effective are, present programs (and their associated assumptions) in the context of a varying environment? (3) What appear to be the principal future effects of alternative adjustments? In this presentation we explore the above questions in one western basin, the Colorado, in which all of the above issues are exemplified.
CASE STUDY: THE COLORADO RIVER BASIN
The Colorado River supplies much of the water needs of seven U.S. states, two Mexican states, and 34 Native American tribes, representing a population of 25 million inhabitants with a projection of 38 million by the year 2020. The Colorado does not discharge a large volume of water. Because of the scale of impoundments and withdrawals relative to its flow, the Colorado has been called the most legislated and managed river in the world. It has also been called the most “cussed” and “discussed” river. As has been well documented, the most important management agreement (the Colorado River Compact of 1922) was based on overestimation of the reliable average annual supply of water (estimated at 16.4 million acre feet) due to a short observational record. Colorado River streamflow however exhibits strong decadal and longer variations. The Colorado system also exhibits the characteristics of a heavily over-allocated or “closed water system.” In such systems, development of mechanisms to allow resource users to acknowledge interdependence and to engage in negotiations and agreements is not only desirable but also necessary. Climate and weather events form a variable background on which these agreements and conflicts are played out. In this context institutional conditions that limit flexibility tend to exacerbate the
underlying resource issues. This presentation describes how lessons from past events and new climate information on the Colorado River Basin inform or do not inform integrated watershed and adaptive management programs intended to preserve and enhance physical, economic, cultural, and environmental values. It begins with an overview of the history of Colorado Basin development and the scales of decision making involved. The decision-making environments are discussed in terms of critical climate-sensitive issues, including interbasin transfers and transboundary responsibilities, Native American rights, environmental requirements, and state water issues.
The Colorado system has experienced drought conditions in six of the last seven years. Until the last few years, the expectation of Colorado River managers was that significant shortages in the Lower Basin would not occur until after 2030. Events such as the drought expose critically vulnerable conditions and, though they warn of potential crisis, they also are opportunities for innovation. Historically, reservoirs and inter-basin transfers have been used to mitigate the effects of short-term drought in the Colorado Basin. The lessons and impacts of these adjustment strategies and more recent settlement agreements are still being gathered. The system’s ability to maintain reliable supply during periods of severe long-term droughts of >10 years (the timescales of development, project implementation, and ecosystem management efforts), known to have occurred in the West over the past 1,000 years, is as yet untested but may be so in the very near future. While recent modeling studies project up to an 18 percent decrease in runoff in the basin under climate change scenarios, just the continuation of drought over the next year will likely induce crisis conditions. Thus the “normal” situation is critical. In the semiarid Southwest, even relatively small changes in precipitation can have large impacts on water supplies. Even in areas where integrated approaches are adopted, cooperation remains mainly crisis driven, inhibiting iterative, long-term collaboration and learning. While opportunities for “win-win” situations and rule changes exist, such changes are extremely difficult to implement. In this context institutional conditions that limit flexibility tend to exacerbate the underlying resource issues.
OPPORTUNITIES FOR LEARNING AND DECISION MAKING UNDER UNCERTAINTY
Learning (and the capacity for employing lessons learned) is of strategic importance in the decades-long process of adapting to global changes, including climatic variations. Even when physical effects or projections can be established with fair confidence, there usually exist large uncertainties about biological and ecological effects and even greater uncertainties with respect to social consequences. Much work and experience has shown that long-term environmental problems can seldom be dealt with by single discrete actions or policies but respond only to continuing, sustained efforts at learning, supported by steady
public attention and visibility. Focusing events provide opportunities for learning. In the West potential water-resource-related focusing events include:
extreme climatic conditions (e.g., drought and floods);
large-scale inter-basin transfers;
quantification of tribal water rights;
an energy crisis;
changing transboundary responsibilities; and
regulatory mandates such as the Endangered Species and Clean Water acts.
Crisis conditions can be said to be reached when focusing events occur concurrently with awareness of a finite time necessary for response. As mentioned above, for many basins in the West the normal situation is critical, and relatively small environmental changes can exceed social thresholds of acceptability and reliability.
Opportunities for learning also arise from deliberate perturbation (e.g., high flow releases) of a system to stimulate monitoring and learning. The idea of “adaptive management” has been widely advocated as a bridge between science and policy with a specific focus on ecosystems. This presentation explores the idea in the context of climatic and other uncertainties but grounds the discussion in the implementation of an actual adaptive management program in the Colorado. Adaptive management has three key tenets: (1) policies are experiments that should be designed to produce usable lessons; (2) it should operate on scales compatible with natural processes, recognizing social and economic viability within functioning ecosystems; and (3) it is realized through effective partnerships among private, local, state, tribal, and federal interests. In a watershed setting this can mean balancing hydropower production, habitat management, conservation, endangered species recovery, and cultural resources in order to experiment, learn, incorporate learning, and adapt—a decidedly idealized view. Each component carries its own type and sources of uncertainty. One goal is to identify the strengths and weaknesses of an “adaptive management approach” for mitigating drought risks in the context of changing climatic baselines and early warning in association with critical thresholds.
CONCLUSIONS: IMPLICATIONS FOR DECISION MAKING
There is increasing awareness that we are engaged in (1) questions about the nature and role of integrated knowledge and uncertainty in complex settings and (2) a social process of risk communication and perception, as opposed to the simple development and dissemination of risk information or even a client-driven “two-way” process. The experience of development in the Colorado in the face of environmental uncertainty clearly illustrates that impacts and interventions
can reverberate through systems in ways that can only be partially traced and predicted. In addition, adjustments and responses in the short term can increase vulnerability over the long term. The discussion here is based on the premise that understanding how effectively society might identify common goals, best use climatic and other information, and prepare for the consequences of future variations and surprises requires identification and evaluation of present systematic efforts (i.e., field-tested alternatives) to experiment, characterize uncertainties, make decisions, and cope with environmental variability across temporal and spatial scales. If lessons learned are to be applied, then a large part of the scientific goal should be to inform processes that can decrease impediments to the flow of information and innovations. This would entail:
clarification of management goals at the human-environment interface;
construction of a cooperative foundation between research and management;
distillation of lessons from comparative appraisals of current and past practices;
understanding and assessing adaptive capacity;
characterizing and communicating uncertainties for both minimizing and managing risk; and
developing effective criteria for validity and acceptability (i.e., robust information in research as well as practical contexts).
In this light a “seamless suite” of products and services for drought risk assessment and management, from national through local, may not be optimal in practice, especially if the goal is improvement of social welfare or at least informing the implementation of better decisions.
Roger S. Pulwarty is a physical scientist in the NOAA/CIRES/Climate Diagnostics Center in Boulder, Colorado. Dr. Pulwarty’s interests are in the role of climate and weather in society-environment interactions and the design of public services to address associated risks. His work has focused on (1) hydroclimatic variability and change; (2) social vulnerability and responses to environmental variations; and (3) the role and use of research-based information in natural resources policy and decision making in the western United States, Latin America, and the Caribbean.
ECOSYSTEM-CLIMATE FEEDBACKS STUDIED WITH AN INTEGRATED GLOBAL SYSTEM MODEL
Ronald G. Prinn
Massachusetts Institute of Technology
The overall goal of our ecosystem-climate research program is to characterize and quantify the feedback mechanisms between terrestrial ecosystems, the climatic system, and air pollution involving the cycles of water, energy, and relevant chemical species. To address this goal we are developing and using an Integrated Global System Model (IGSM) that includes (1) dynamic and linked terrestrial hydrology and ecology, including the MBL Terrestrial Ecosystems Model (TEM); (2) comprehensive coupled physical climate (MIT two-dimensional atmosphere and three-dimensional ocean); and (3) MIT atmospheric chemistry (gaseous and aqueous phase chemical processes). The IGSM also includes a detailed global economics model, including emissions from industrial and agricultural activity. The integrated models represent the major complex biological systems on earth and span the scales from local to global.
With our coupled models we have quantified the combined effects of air pollution (O3), rising CO2, and climate change on the productivity and distribution of vegetation globally. We have also determined how changes in land ecosystems, caused by pollution and climate change, can feed back to climate through changes in carbon storage. We have calculated past and future carbon dioxide and methane fluxes from northern high latitudes under the joint influence of rising CO2 levels and rising Arctic temperatures. We have also computed substantial changes in soil N2O emissions under the joint influences of changing temperatures, rainfall, and soil carbon. As the impacts of multiple stressors acting simultaneously on forest production are determined, their roles in amplifying or damping regional disparities are being elucidated. Toward these ends we have improved our Terrestrial Ecosystem Model and Atmospheric Chemistry Models to facilitate their interaction. We have also further developed our 3D Ocean Circulation Model to incorporate biogeochemical cycles. We also adapt the NCAR MATCH, CCM3, and CAM3 3D models for selected atmospheric chemistry studies. Our work is providing significant information for understanding how our future global environment will evolve under the joint effects of growing world population, changing technological and agricultural practices, and economic development. We argue that uncertainties in most of the relevant feedback processes are large. Therefore, to understand the above interactions we include comprehensive studies of the sensitivity of our conclusions to critical input assumptions, and calculations of the probability distributions of critical output variables. We address this through the use of multiple (ensemble) simulations, flexible models, and powerful (probabilistic collocation) methods to compute uncertainties. There are significant educational by-products of this research designed to effectively communicate results
to students, fellow researchers, journalists, industry, and environmental policy makers. We are also making contributions to general methodologies to study and numerically simulate very complex and interactive spatially and temporally resolved phenomena using distributed memory computers. Much of our research has already appeared in multiple papers in Journal of Geophysical Research, Tellus, Geophysical Research Letters, Climatic Change, Global Biogeochemical Cycles, Journal of Vegetation Science, Journal of Climate, and other journals, and several papers are under review. Public access to our research, including reports and journal reprints, is available through our extensive websites: Joint Program on the Science and Policy of Global Change (http://mit.edu/globalchange/) and Center for Global Change Science (http://mit.edu/cgcs/).
Here we present the results of three of the projects.
INFLUENCE OF CLIMATE AND AIR POLLUTION ON ECOSYSTEM CARBON FLUXES
Several environmental factors influence carbon sequestration in natural terrestrial ecosystems, including climate variability and change, atmospheric carbon dioxide concentrations, ozone pollution, and atmospheric nitrogen deposition. To explore the relative importance of these factors on historical carbon sequestration, we have conducted a series of global simulations with a modified version of the Terrestrial Ecosystem Model. Model modifications include a more detailed representation of soil nitrogen pools and fluxes to better account for the influence of nitrogen deposition, nitrogen fixation, trace N gas emissions, and leaching losses of nitrate and dissolved organic nitrogen on terrestrial carbon and nitrogen dynamics. Initial results indicate that natural terrestrial ecosystems accumulated 54.8 Pg C during the 20th century as a result of CO2 fertilization (39.2 Pg C), atmospheric nitrogen deposition (19.7 Pg C), and climate variability and change (3.1 Pg C); ozone pollution reduced the potential carbon sequestration benefits of these other factors by 7.2 Pg C. Over this time period, the rate of carbon accumulation increased from about 1.0 Pg C per year in the 1900s to 1.6 Pg C per year in the 1990s. Carbon sequestration is not uniformly distributed across the globe. Preliminary analyses also suggest that carbon losses associated with land use change over this time period would substantially reduce our estimate of carbon sequestration. Looking to the future, lowering of ozone levels resulting from future air pollution policies is estimated to increase carbon uptake by terrestrial ecosystems. To better account for the effects of human and natural disturbances, we are currently developing datasets and revising algorithms to consider the effects of agriculture, fire, logging, and insect infestations on terrestrial carbon and nitrogen dynamics.
CLIMATIC INFLUENCES ON METHANE SURFACE FLUXES
We have estimated fluxes by combining observations and models using (1) methane observations: high-frequency (13: AGAGE, CMDL, etc.) and Flask (41 comprehensive and 32 more intermittent: CMDL, CSIRO, etc.) monthly mean observations between 1996 and 2001; and (2) Global 3D MATCH model: interannually varying transport (NCEP) used with 1.8 deg. × 1.8 deg. resolution and 28 levels to create the CH4 response of each site to monthly pulses from individual regional processes (sensitivity matrix). Using an annually repeating time/ space-varying model OH tuned to AGAGE CH3CCl3 observations, the Kalman Filter is used to solve for seven seasonally varying processes (three wetland, three biomass burning, rice) as monthly varying fluxes; and two pseudo-steady processes (animals and water, coal and gas) as constant fluxes. Deduced interannual variability (monthly anomalies) is large with a 32-33 Tg/yr total emissions increase in 1998 coinciding with El Niño and global wildfires. Northern/tropical wetlands and rice region emissions dominate the total variability. Rice areas (including proximal wetlands) are responsible for 8-17 Tg/yr of this. Wetlands dominate the remainder, but boreal fires in Siberia may have also contributed to our deduced strong northern wetlands increase. Compared to previous estimates, energy-related emissions are smaller (decrease in Russia?) and emissions from rice-growing regions are larger (proximal forests or wetlands?). The computed seasonal flux cycles capture the expected seasonal cycles (but rice growing peaks earlier).
We have also used TEM to study how rates of methane (CH4) emissions and consumption in high-latitude soils of the Northern Hemisphere have changed over the past century in response to observed changes in the region’s climate. We estimate that the net emissions of CH4 (emissions minus consumption) from these soils have increased by an average .08 Tg CH4 yr–1 during the 20th century. Our estimate of the annual net emission rate at the end of the century for the region is 51 Tg CH4 yr–1. Russia, Canada, and Alaska are the major CH4 regional sources to the atmosphere, responsible for 64 percent, 11 percent, and 7 percent of these net emissions, respectively. Our simulations indicate that large interannual variability in net CH4 emissions occurred over the last century. Our analyses of the responses of net CH4 emissions to the past climate change suggest that future global warming will increase net CH4 emissions from the Pan-Arctic region. The higher net CH4 emissions may increase atmospheric CH4 concentrations to provide a major positive feedback to the climate system.
CLIMATIC AND NUTRIENT IMPACTS ON NITROUS OXIDE EMISSIONS
Natural terrestrial fluxes of N2O from soils are important contributors to the global budget of this greenhouse gas. The IGSM incorporates the global Natural Emissions Model (NEM) for soil biogenic N2O emissions, which has
2.5° × 2.5° spatial resolution. It is a process-oriented biogeochemical model including the processes for decomposition, nitrification, and dentrification. The model takes into account the spatial and temporal variability of the driving variables, which include soil texture, vegetation type, total soil organic carbon, and climate parameters. Climatic influences, particularly temperature and precipitation, determine dynamic soil temperature and moisture profiles and shifts of aerobic-anaerobic conditions. The major biogeochemical processes included in the model are decomposition, nitrification, ammonium and nitrate absorption and leaching, ammonia emission, and denitrification. For present-day climate and soil datasets, NEM predicts an annual flux of 11.3 Tg-N (17.8 Tg N2O). NEM predicts large emissions from tropical soils, which is qualitatively consistent with the observed latitudinal gradient for N2O, and in situ flux measurements. Predicted emissions of N2O from runs of the NEM through 2100 indicate significant sensitivity to outputs from the climate (temperature, precipitation) and TEM (total soil carbon) models. Two NEM runs driven by climate outputs only and climate plus TEM outputs indicate that climate and soil carbon changes contribute about equally to the predicted very significant increase in N2O emissions. Since soil carbon and temperature are predicted to change in the future, the importance of including the feedbacks to climate forcing involving changing natural emissions of N2O is evident.
Ronald G. Prinn is TEPCO Professor of Atmospheric Chemistry, director of the Center for Global Change Science, and co-director of the Joint Program on the Science and Policy of Global Change at the Massachusetts Institute of Technology. Dr. Prinn’s research interests incorporate the chemistry, dynamics, and physics of the atmospheres of the earth and other planets, and the chemical evolution of atmospheres. He is currently involved in a wide range of projects in atmospheric chemistry and biogeochemistry, climate science, and integrated assessment of science and policy regarding climate change. He received his Sc.D. in chemistry from the Massachusetts Institute of Technology.
THE ROLE OF BIOGEOCHEMISTRY IN THE CLIMATE SYSTEM: EARLY EXPERIENCES FROM THE NCAR COMMUNITY CLIMATE SYSTEM MODEL
Scott C. Doney
Woods Hole Oceanographic Institution
The biogeochemical cycles of carbon, nitrogen, sulfur, and several other elements are integral components of the climate system that, until recently, have been neglected to a large degree in traditional physical climate studies. Perturbations to the planet’s biogeochemical systems affect climate through changes in atmospheric composition, land surface properties, and ecological rates, which together in turn alter radiative balance and energy and water cycles. Several climate modeling groups have begun to include biogeochemical and ecological components into the coupled 3-D ocean, atmosphere, land climate models used to assess past, present, and future climate change. Here I discuss early results with the NCAR Community Climate System Model (CCSM). I focus on carbon-climate interactions resulting from anthropogenic fossil fuel combustion and climate warming as this example illustrates the complicated nature of the underlying coupled physical-biological interactions. I conclude with a brief overview of other biogeochemical processes being incorporated in the CCSM that may introduce important feedback mechanisms, nonlinearities, and thresholds to the climate system.
CARBON-CLIMATE EXPERIMENT OVERVIEW
A new three-dimensional global coupled carbon-climate model is presented in the framework of the Community Climate System Model (CSM 1.4) (Doney et al., 2006). A 1,000-year control simulation has stable global annual mean surface temperature and atmospheric CO2 with no flux adjustment in either physics or biogeochemistry. At low frequencies (timescale > 20 years), the ocean tends to damp (20-25 percent) slow, natural variations in atmospheric CO2 generated by the terrestrial biosphere. Transient experiments (1820-2100) (Fung et al., 2005) show that carbon sink strengths are inversely related to the rate of fossil fuel emissions, so that carbon storage capacities of the land and oceans decrease and climate warming accelerates with faster CO2 emissions (Figure 1). There is a positive amplification between the carbon and climate systems, so that climate warming acts to increase the airborne fraction of anthropogenic CO2 and amplify the climate change itself. Globally, the amplification is small at the end of the
21st century in our model because of its low transient climate response and the near-cancellation between large regional changes in the hydrological and ecosystem responses.
The physical climate core of the coupled carbon-climate model is a modified version of National Center for Atmospheric Research CSM1.4, which consists of atmosphere, land, ocean, and ice components that are coupled via a flux coupler. Into CSM1.4 are embedded a modified version of the terrestrial biogeochemistry model CASA, and a modified version of the OCMIP-2 oceanic biogeochemistry model. CASA follows the life cycles of plant functional types from carbon assimilation via photosynthesis, to mortality and decomposition, and the return of CO2 to the atmosphere via microbial respiration. There are three live vegetation pools and nine soil pools, and the rates of carbon transfer among them are climate
sensitive. The carbon cycle is coupled to the water cycle via transpiration and to the energy cycle via dynamic leaf phenology (and hence albedo). A terrestrial CO2 fertilization effect is possible in the model because carbon assimilation via the Rubisco enzyme is limited by internal leaf CO2 concentrations; net primary productivity (NPP) thus increases with external atmospheric CO2 concentrations, eventually saturating at high CO2 levels. The ocean biogeochemical model includes in simplified form the main processes for the solubility carbon pump, organic and inorganic biological carbon pumps, and air-sea CO2 flux. New/export production is computed prognostically as a function of light, temperature, phosphate, and iron concentrations. A fully dynamic iron cycle also has been added, including atmospheric dust deposition/iron dissolution, biological uptake, vertical particle transport, and scavenging.
A sequential spin-up strategy is utilized to minimize the coupling shock and drifts in land and ocean carbon inventories. In the 1,000-year control, global annual mean surface temperature is ±0.10 K and atmospheric CO2 is ±1.2 ppm (1σ) (Figure 2). The control simulation compares reasonably well against observations for key annual mean and seasonal carbon cycle metrics; regional biases in coupled model physics, however, propagate clearly into biogeochemical error patterns. Simulated interannual to centennial variability in atmospheric CO2 is dominated by terrestrial carbon flux variability, ±0.69 Pg C y–1, reflecting
primarily regional changes in net primary production modulated by moisture stress. Power spectra of global CO2 fluxes are white on timescales beyond a few years, and thus most of the variance is concentrated at high frequencies (timescale < 4 years). Model variability in air-sea CO2 fluxes, ±0.10 Pg C y–1 (1σ), is generated by variability in temperature, wind speed, export production, and mixing/upwelling.
Climate change is expected to influence the capacities of the land and oceans to act as repositories for anthropogenic CO2 and hence provide a feedback to climate change. A series of experiments with the coupled carbon-climate model shows that carbon sink strengths are inversely related to the rate of fossil fuel emissions, so that carbon storage capacities of the land and oceans decrease and climate warming accelerates with faster CO2 emissions. Furthermore, there is a positive feedback between the carbon and climate systems, so that climate warming acts to increase the airborne fraction of anthropogenic CO2 and amplify the climate change itself. Globally, the amplification is small at the end of the 21st century in this model because of its low transient climate response and the near-cancellation between large regional changes in the hydrological and ecosystem responses. Analysis of our results in the context of comparable models suggests that destabilization of the tropical land sink is qualitatively robust, though its degree is uncertain.
THE NEXT STEPS FORWARD
The preliminary treatment of the carbon cycle in CSM 1 is incomplete in many regards. For example, the terrestrial biogeochemical component neglects many of the factors thought to govern historical and future carbon sinks, such as land use changes, disturbance/fire, dynamic vegetation, and nitrogen limitation. Similarly for the ocean system, a number of other hypotheses have been proposed on how the planet’s biogeochemical systems can alter climate and ecosystems. These include variability in ocean carbon storage driven by changes in atmospheric dust (iron limitation) and the impacts of ocean acidification on marine calcifiers (corals, pteropods, coccolithophores, etc.). All of these processes (along with reactive atmospheric chemistry) are being incorporated currently into a new version of the CCSM3. Plans are also underway, though at a very early stage, for including interactive human decisions, in effect moving CCSM toward a full earth system modeling capability.
Doney, S. C., K. Lindsay, I. Fung, and J. John. 2006. Natural variability in a stable 1000 year coupled climate-carbon cycle simulation. Journal of Climate 19(13):3033-3054.
Fung, I., S. C. Doney, K. Lindsay, and J. John, 2005. Evolution of carbon sinks in a changing climate. Proceedings of the National Academy of Sciences U.S.A. 102:11201-11206.
Scott C. Doney is a senior scientist at the Woods Hole Oceanographic Institution. Dr. Doney’s research interests include marine biogeochemistry and ecosystem dynamics, large-scale ocean circulation and tracers, air-sea gas exchange, and the global carbon cycle. He received his Ph.D. in chemical oceanography from the MIT/Woods Hole Oceanographic Institution Joint Program.
UNDERSTANDING ATMOSPHERE-BIOSPHERE INTERACTIONS: THE ROLE OF BIOGENIC VOLATILE ORGANIC COMPOUNDS
National Center for Atmospheric Research
Reactive biogenic volatile organic compounds (BVOC) have a substantial impact on air quality, especially ozone and particles, and the ability of the atmosphere to remove greenhouse gases, such as methane (Sanderson et al., 2003; Went, 1960). They are also a component of the carbon cycle that produces ~ 4 Pg of CO2 each year (Guenther, 2002). These atmospheric chemical composition changes could perturb physical climate and the biosphere. Since BVOC emission rates are very sensitive to physical, chemical, and biological driving variables, they may have a significant role in earth system interactions and feedbacks, including those illustrated in Figure 1. However, these processes are complex, nonlinear, and difficult to predict given our current limited understanding. Increases in emissions of some VOCs are likely to result in increases of gases that can increase radiative forcing, but this would be accompanied by an increase in organic particles, which could decrease radiative forcing.
Although there are hundreds of different BVOC species emitted into the atmosphere, one compound (isoprene) contributes about half of the total annual global flux (Guenther et al., 1995). Other BVOC, such as β-caryophyllene, are particularly important for the production of secondary organic aerosol. There are ~ 50 BVOC chemical species that have an important role for atmospheric chemistry, either because they are emitted in large amounts or because they are particularly important for some atmospheric process (Guenther et al., 2000). BVOCs that have important ecological roles may differ from those with important atmospheric roles. For example, some BVOCs used as signaling compounds are present in the atmosphere at extremely low concentrations and have a negligible impact on the atmosphere.
RESPONSE TO CHANGES IN ATMOSPHERIC CHEMICAL COMPOSITION
Isoprene emission rates are sensitive to atmospheric trace gas levels. Isoprene emission can increase when ozone is increased from background to levels representative of a polluted city (e.g., Velikova et al., 2005). However, this may not be sustained with long-term (months) exposure (e.g., Ennis et al., 1990). In addition, isoprene emission can decrease in response to an increase in CO2 (e.g., Rosenstiel et al., 2003). However, this decrease is minimized when plants are grown at less than optimal soil moisture (Pegoraro et al., 2004).
Very little is known about the potential impact of a changing atmospheric oxidation capacity on the use of BVOC signaling compounds for defense or attraction. The oxidation capacity of the atmosphere determines the lifetime of most BVOCs and so could limit the effective range over which organisms can use signaling compounds. The ecological implications of this change have not been quantified.
RESPONSE TO CLIMATE CHANGE
Isoprene emission can be relatively insensitive to drought. Some studies show that a decrease in soil moisture that results in much lower photosynthesis and stomatal conductance can cause little or no decrease in isoprene emission until soil moisture reaches the point where photosynthesis ceases and the leaves begin to wilt (Pegoraro et al., 2004). There is occasionally even an increase, possibly due to increasing leaf temperatures associated with decreased transpiration. This may at least partly explain the surprisingly large seasonal variations in isoprene emissions that have been observed in tropical rainforests, which are the dominant global source of isoprene emission (Guenther et al., 1999). Isoprene emissions in the dry season can be a factor of 3 higher than during the wet season even after accounting for the known response of emissions to changes in tem-
perature and solar radiation. The unexplained variations appear to be negatively correlated with soil moisture.
Isoprene emission is very sensitive to temperature and solar radiation. This is compounded by the ability of plants to adapt to changing temperature and light and results in even higher emissions associated with extended exposure to temperature and light (Guenther et al., 1999). As a result, a long-term 3K increase in temperature could result in an increase in isoprene emission of as much as a factor of 2.
RESPONSE TO BIOLOGICAL CHANGE
Enclosure studies have shown that biological stresses (e.g., herbivory, fungal or viral infections, insect pests) can result in large increases in biogenic VOC emissions (e.g., Wildt et al., 2003). However, this phenomenon has not been investigated on canopy or landscape scales. Increasing levels of biological stress could be associated with future global change and would likely lead to elevated emissions of a variety of BVOCs.
Isoprene and other terpenoid emission rates from different plant species range across three to four orders of magnitude (Guenther et al., 2000). Landscape average emissions can vary more than an order of magnitude depending on plant species composition. On a global scale ~30 percent of all woody plants emit isoprene (Guenther et al., 1995). Isoprene emitters are found in a wide variety of landscapes, including tropical, temperate, and boreal ecosystems. There tends to be a higher abundance of isoprene emitters in disturbed (early successional) landscapes. In addition, many of the fast-growing tree plantation species (e.g, poplar, eucalyptus, oil palm, rubber tree) have extremely high isoprene emissions (Guenther et al., 2000). Large monoculture plantations of these species will likely have a dramatic impact on local air chemistry.
Ennis, C. A., A. L. Lazrus, P. R. Zimmerman, and R. K. Monson. 1990. Flux determination and physiological response in exposure of red spruce to gaseous hydrogen peroxide, ozone, and sulfur dioxide. Tellus Series B-Chemical and Physical Meteorology 42B:183-199.
Guenther, A. 2002. The contribution of reactive carbon emissions from vegetation to the carbon balance of terrestrial ecosystems. Chemosphere 49(8):837-844.
Guenther, A., C. N. Hewitt, D. Erickson, R. Fall, C. Geron, T. Graedel, P. Harley, L. Klinger, M. Lerdau, W. A. Mckay, T. Pierce, B. Scholes, R. Steinbrecher, R. Tallamraju, J. Taylor, and P. Zimmerman. 1995. A global-model of natural volatile organic-compound emissions. Journal of Geophysical Research-Atmospheres 100(D5):8873-8892.
Guenther, A., B. Baugh, G. Brasseur, J. Greenberg, P. Harley, L. Klinger, D. Serca, and L. Vierling. 1999. Isoprene emission estimates and uncertainties for the Central African EXPRESSO study domain. Journal of Geophysical Research-Atmospheres 104(D23):30625-30639.
Guenther, A., C. Geron, T. Pierce, B. Lamb, P. Harley, and R. Fall. 2000. Natural emissions of non-methane volatile organic compounds, carbon monoxide, and oxides of nitrogen from North America. Atmospheric Environment 34(12-14):2205-2230.
Pegoraro, E., A. Rey, R. Murthey, E. Bobich, G. Barron-Gafford, K. Grieve, and Y. Malhi. 2004. Effect of CO2 concentration and vapour pressure deficit on isoprene emission from leaves of Populus deltoides during drought. Functional Plant Biology 31(12).
Rosenstiel, T. N., M. J. Potosnak, K. L. Griffin, R. Fall, and R. K. Monson. 2003. Increased CO2 uncouples growth from isoprene emission in an agriforest ecosystem. Nature advance online publication, January 5 (doi:10.1038/nature 01312).
Sanderson, M. G., C. D. Jones, W. J. Collins, C. E. Johnson, and R. G. Derwent. 2003. Effect of climate change on isoprene emissions and surface ozone levels. Geophysical Research Letters 30(18):1936, doi:10.1029/2003GL017642.
Velikova, V., P. Pinelli, S. Pasqualini, L. Reale, F. Ferranti, and F. Loreto. 2005 Isoprene decreases the concentration of nitric oxide in leaves exposed to elevated ozone. New Phytologist 166(2):419-426.
Went, F. W. 1960. Blue hazes in the atmosphere. Nature 187(4738):641-643.
Wildt, J., K. Kobel, G. Schuh-Thomas, and A. C. Heiden. 2003. Emissions of oxygenated volatile organic compounds from plants. Part II: Emissions of saturated aldehydes. Journal of Atmospheric Chemistry 45(2):24.
Alex Guenther is a senior scientist, section head, and group leader of the Biosphere-Atmosphere Interactions Group of the Atmospheric Chemistry Division at the National Center for Atmospheric Research. Dr. Guenther’s research interests include phytogeography and biogeochemistry; biosphere-atmosphere interactions; developing and applying trace gas and aerosol flux measurement techniques; understanding biological, chemical, and physical controls of trace gas fluxes; numerical modeling of chemical exchange between terrestrial ecosystems and the atmosphere; impact of biogenic emissions; and ecosystem uptake and fire emissions on atmospheric chemistry and sustainability. He received his Ph.D. from the Department of Civil and Environmental Engineering at Washington State University.
HUMAN-EARTH SYSTEM INTERACTIONS
J. M. Reilly
Massachusetts Institute of Technology
The societal relevance of understanding complexities of earth system interactions is that human activity both affects these systems and is affected by changes in them. The goal of our research in this regard is to understand the complex and dynamic interactions between human and earth systems at the global scale, but resolved regionally. Our approach is to link a global model of the world economy, the Emissions Prediction and Policy Analysis (EPPA) model, with a comprehensive model of terrestrial hydrology and ecology and the physical climate system as controlled by atmosphere and ocean processes as they interact with terrestrial systems. At present, the physical and ecological system is resolved at a level that has come to be known as an earth system model of intermediate complexity, with less spatial resolution than a full-scale 3-dimensional Atmosphere-Ocean General Circulation Model (AOGCM) but with far more detail than the highly parameterized energy-balance-type models that have been widely used in integrated assessment. We sacrifice further resolution in the modeling of individual components of the earth system so that the Integrated Global System Model (IGSM) is computationally efficient, allowing us to evaluate very large ensemble runs (order 102-103). The desire to produce large ensemble simulations is driven by our interest in understanding the phenomenon of global environmental change as one of risk management. Research and modeling of the interaction of physical and ecological earth systems is described by Prinn (2006) and in greater detail in Sokolov et al. (2005).
The standard approach for evaluating the economics of climate change, or many policy problems, is to study the policy issue in isolation, focusing on the efficiency of economic instruments and calculation of an optimal policy. In contrast, our approach has been to explicitly recognize that economic systems are complex: multiple economic and environmental problems interact and these interactions strongly affect the efficiency and effectiveness of policy instruments and lead to very different conclusions than one would obtain absent this more realistic representation of economic activity and its relationship to the natural environment. In this regard, it is useful to consider three broad sets of complex interactions. Those among: (1) economic policies directed toward different economic problems, (2) the economy and the changing set of technological options as they affect abatement potential and cost, and (3) the economy and the physical-ecological earth system. And, in fact, there are strong interactions among all of these categories. Thus, the simplifying assumptions often made in research to allow separate study of just the economic system, a single country or sector, or climate in isolation of other economic issues are invalid. Whether these complexities strongly affect conclusions one might reach of viable policy options is
a major focus of our ongoing research program. Published research appears in journals such as the Journal of Environmental Economics and Management, The Energy Journal, Energy Economics, Environmental Modeling and Assessment, Climatic Change, Science, Nature, Energy Policy, Climate Policy, and others. A description of the EPPA component and the IGSM and freely available reports and reprints are on the Joint Program on the Science and Policy of Global Change website, http://web.mit.edu/globalchange/www/. Here, I would report very briefly some results from our program on each of the three sets of interactions above, to illustrate how modeling the complexity of the system leads to different results than one might otherwise expect. This is not intended to be a comprehensive review of these topics as in many cases there is a considerable body of accumulated research.
COMPLEX INTERACTIONS AMONG ECONOMIC POLICIES
In an idealized economy the prices of goods reflect the marginal cost of producing them, and consumers who base decisions on these prices equate their marginal value of use of the good to these prices. The widely demonstrated result in neoclassical economics is that the equalization of marginal cost and marginal value through a price system, in this idealized world, results in an optimal use of resources. Environmental economics adds to this issue, by observing that an environmental problem like climate change is an “externality” in that, absent a specific climate policy, there is no price paid for disposing of greenhouse gases in the atmosphere, prices of goods and services that emit them thus do not reflect the damages associated with emissions, and emissions and consumption of emission-intensive goods are too high. In the idealized economy, one finds a strong theoretical result that an economic instrument that prices carbon abatement equally across sectors and regions is “cost effective” in the sense that it achieves that level of reduction at the least cost, and “optimal” or “efficient” if the carbon price is also determined to be equal to the marginal benefit in terms of reduced damage.
There are many widely recognized ways in which real-world economies depart from the idealized neoclassical economy. This recognition is hardly new; it was formulated in the 1950s as the “theory of the second best” and also has had implications in international trade where it was described as the paradox of “immiserizing growth.” For a review of these issues, see Babiker et al. (2003a). Violations of the idealized economy are variously described as preexisting distortions (other taxes that do not reflect a specific externality), externalities (other than the climate change itself) that are not priced at all or are mispriced, and cases where actors in the economy are large enough to affect prices and this affects (or should be considered) in their decisions. The tax system of an economy is one important distortion, and important interactions of climate policy and tax policy have led to findings showing a “double dividend” for the U.S. under some
cases, but we have found that this does not necessarily translate to other countries because it depends on the specifics of the tax system, so a double dividend was less likely to exist in many European countries (Babiker et al., 2003b). We have also shown that divergence from an economy-wide cap and trade system may be economically superior to a cap and trade system that equalizes the marginal cost of carbon across sectors (Babiker et al., 2004). This has further implications for international permit trading, where we find that autarkic compliance with a cap may be economically superior to an international permit trading system (Metcalf et al., 2004). This can be traced to the relative level of taxation of fuels (Paltsev et al., 2004). A further implication is that simple models where the carbon permit price (marginal abatement cost) is taken as an indicator of the cost of the carbon policy can be highly misleading. For example, the double dividend finding is one where it is possible that, by recycling revenue from a carbon tax to offset existing distortionary capital and labor taxes, the carbon policy has a marginal social benefit quite apart from any climate damage avoidance (Babiker et al., 2003a). In other cases interaction of the carbon policy with existing energy taxes can lead the average social cost of the carbon policy to be on the order of five times higher than the marginal carbon reduction cost (Paltsev et al., 2004). Agriculture/land use is an important source of emissions and/or a potential sink particularly in developing countries (Hyman et al., 2003) and is a sector with extensive policy intervention (preexisting distortions). Research on the interactions of climate policy and agricultural policy has been limited or nonexistent to date, but accurate representation of the agriculture sector and policies is needed to capture the interactions between climate and other policies that affect agriculture. Obviously, agriculture is also a sector sensitive to environmental change, and so that interaction among agricultural policies and the natural environment itself is essential.
INTERACTIONS BETWEEN THE ECONOMY AND CHANGING TECHNOLOGY
A description of the global economy embodied in a computable general equilibrium model such as our Emissions Prediction and Policy Analysis (EPPA) model represents explicitly or implicitly the technological options open to the economy over time (Jacoby et al., 2006; Paltsev et al., 2005a). Much effort has been invested in the research community to develop endogenous models of technical change, recognizing that price or other economic signals resulting from a climate policy would likely change the pace and direction of innovation. Here, one must realize that the task of endogenously describing technical change requires the modeler to describe all possible blueprints of relevant technologies and their ultimate cost and the cost of discovering them. Essentially this demands the modeler to know the details of technologies ahead of those who are working to discover them. While this is an impossibility—if we knew it we would not have to discover it—there are worthwhile avenues of research. Our approach has
been to first describe the current state of technological options, and examine their changing potential as resource availabilities and prices changed, as in the case of carbon sequestration (Jacoby et al., 2006). While at the time this research was being done, natural gas combined-cycle technology was seen as the dominant technology and thus the likely future in a carbon-constrained world, we found that rising gas prices would likely mean that integrated gasification of coal with sequestration was much more promising in the longer run. Gas prices have since risen dramatically, and this result would now surprise no one, but the only hope of escaping whatever the current mindset with regard to prices is to try to represent underlying fundamentals of demand and resource availability. We have further explored the value of carbon sequestration in oceans, recognizing that ultimately the carbon will end up in the ocean anyway, so that it was properly investigated as “temporary storage” (McFarland et al., 2004). This work found that there could be no value to temporary storage, and any value depended on the existence of a backstop that would cap the price of carbon or include a damage function and optimal carbon price that would likely mean ever-increasing atmospheric carbon levels. Modeling the explicit technological options where there are diverse technological options such as transportation can be daunting (Schafer and Jacoby, 2003), with the need to consider the evolution of demand, changing technological options, and interactions with existing policies such as fuel taxes (Paltsev el al., 2005b).
Important in the issue of trying to represent technical change is to represent the resources in the economy that are devoted to innovation and the fact that allocating these resources to climate change mitigation (or adaptation) means reallocating them away from other research endeavors (Sue Wing, 2003). In recent work, we are following up on preliminary investigations (Jacoby et al., 2006) to unravel the processes at work that may explain why technologies penetrate in the classic S-shape and exhibit declining costs. Several processes are at work, including vintaging/irreversibilities in the capital stock for the existing technology, adjustment costs due to rapid scaling up of the capacity to produce the new technology, monopoly rents associated with at least initially unique skills/ knowledge and possibly enforced through intellectual property rights laws, and finally the innovation/learning process which may contribute to improvements in the technology. The technology may also depend on a resource that is varied in quality and is more or less accessible (e.g., wind or solar) or competes with other uses (e.g., biomass competition with food for land). Different combinations of these phenomena can lead to S-shaped penetration and/or declining cost. Much work has focused on learning curves, assuming the declining cost reflects innovation. Such relatively simplistic analyses would suggest that subsidization or other stimulation of the market will push the technology cost down a “learning curve,” but this can be misleading to the extent other processes are at work. Our preliminary results suggest that subsidization can lead to waste by increasing adjustment costs if that is the primary explanation, extra profits with no improve-
ment in the technology if monopoly rents are the primary explanation, or advance of the technology if learning explains the falling costs.
Key to modeling technical change is to recognize that knowledge is itself a problem for neoclassical economics because the marginal cost of using knowledge, once discovered, is zero, but pricing knowledge at zero does not compensate for the cost of discovering it, thus the existence of intellectual property rights protection that tries to balance compensation for innovation through granting of monopoly rights with economic efficiency of making the technology widely available. Also, there are typically knowledge spillovers so that even with the patent protection, developers may never fully capture the returns to investments. With some advocating a technology policy to solve the climate problem, careful examination of these complex issues is critical. In one study of the Dutch economy a fully dynamic, forward-looking, multisector general equilibrium setting, including technology spillovers examines this issue (Otto et al., 2006). In this study, effective technology policy can increase the needed carbon price and the economic cost of climate policy in absolute terms, albeit the economy is much larger with effective technology policy than without. We have found a similar result in a much simpler framework, where we imagine that, exogenously, gas resources are much larger than any conventional estimate. One might expect this to lead to substitution away from coal, oil, shale oil, and the like, thus reducing emissions of CO2. Instead, CO2 emissions increased, again because the growth effect of lower gas prices dominated the substitution effect. Similarly exogenous bias toward growth of the service sector—while reducing emissions somewhat compared with the case of neutral growth in sectors—has a much smaller effect than one might expect given the low energy intensity of the sector because of the interindustry demands of the service sector for relatively energy intensive goods and services (e.g., transportation). While initially surprising or counterintuitive, there is an intuition behind these results, and they suggest the need for consideration of the complex interactions of technical change, growth, and climate policy.
INTERACTIONS BETWEEN THE ECONOMY AND THE PHYSICAL-ECOLOGICAL EARTH SYSTEM
The grand statement of the problem of interaction of the economy and the physical-ecological earth system is the formal statement of the global warming potential index issue, extended beyond the conventional greenhouse gases to other pollutants and beyond warming to the direct or other effects of substances of concern (Reilly and Richards, 1993; Reilly et al., 2003). The objective function in this problem is to minimize the burden on the economy taking into account the cost of controlling various greenhouse substances and the damage they cause. This is an exceedingly demanding research agenda in that it requires valuation of the multiple effects of global warming (crops, health, extreme events, ecological
disruption), the multiple effects of greenhouse substances (CO2 fertilization, damaging effects on vegetation and health of tropospheric ozone and of aerosols), the varying costs of abatement of different substances, and the complex interactions (in the atmosphere due to chemistry, in mitigation cost due to shared generating processes, and feedbacks such as environment on carbon uptake). We have considered this starting from a relatively complete description of shared generating processes and well-articulated model of the complexity of atmospheric chemistry to show that the 100-year GWPs undervalue methane abatement substantially (Reilly et al., 1999). We have studied this within the context of a forward-looking economic model with climate damages explicitly valued to study the implications of alternative representations of the discount rate, finding that if the declining discount rate formulation some have proposed for long-term problems is correct, then concern shifts to the very long-lived substances (Reilly et al., 2001). And again we used the more fully articulated physical model to show that under a policy to stabilize CO2 at 550 ppm the effects of undervaluing methane using GWPs persists for 250 to 300 years (Sarfim et al., 2005). And most recently we have examined the effects of common air pollutants on climate as already discussed by Prinn showing countervailing effects at least in terms of global mean surface temperature changes (Prinn et al., 2006).
A recent focus is on the feedbacks of changing environment on the economy itself. We have showed that tropospheric ozone could significantly reduce carbon uptake by vegetation and thus increase the cost of meeting a 550 ppm stabilization target by 6 to 21% (Felzer et al., 2005). The surprisingly large cost addition results from valuing the cost change at the margin. We have also evaluated multiple environmental changes (climate, CO2, O3, and consequent changes in soils) on agricultural crops and the economy. This shows significant current ozone damage in the United States, Europe, and China (4-9% loss of the value of crop production), and the potential for this loss to increase substantially even if ozone precursors are controlled (Reilly et al., 2004, 2006). At the same time, this shows a generally beneficial effect of climate/CO2 largely driven by the positive CO2 fertilization effect. We find that the agricultural sector “adapts” almost completely to these changes in terms of the production effect, but that the economic effect is measured in other sectors as resources shift into or out of agriculture. So, the cost of adaptation, in terms of % loss of the value of crop production, is about ½ the direct yield loss even though production changes very little in response to fairly severe productivity shocks. Notably, international trade has effects across different regions because of the differential productivity effects. We have also examined the health effects of air pollution and the resultant effects on the economy. So far we have focused on the United States and, preliminarily, China (Yang et al., 2005; Matus et al., 2006; Matus, 2005), finding a substantial remaining burden of air pollution on the economy, particularly of China, where the remaining burden is estimated at 10% of macroeconomic consumption. Our interest in this work is to complete the modeling of feedbacks on the earth sys-
tem. Effects on agriculture, and changing production and trade, mean changes in land use in producing regions, with consequent effects on the biogeochemical cycle. Abandonment of land, or reduced intensity of use, would mean increased carbon uptake, while expansion of intensified use would likely lead to release of carbon and other greenhouse gases. We expect important interactions with mitigation options, in particular biomass energy that competes for land and is similarly affected by environmental change. Air pollution health effects, through their effect on the economy, may also affect emissions, but we are also interested in joint policy solutions whereby a climate policy may affect health via its effect on air pollution emissions, or conversely air pollution policy driven by the desire to reduce health effects may lead to changes in climate.
An important goal for us with regard to analysis of impacts is to value damages in a manner consistent with mitigation costs to make for a more consistent comparison of benefits and costs. Mitigation cost analysis works on a rich theoretical and empirical basis, developed as computable general equilibrium models that can be simulated dynamically. Damage assessment can be extremely ad hoc, multiplying a constant wage rate or value of life times an estimate of hours or lives lost. In this regard, one of the early findings is that even though pollution levels can fall over time, the absolute damages may rise over time because real wages and other prices rise. We also find significant improvement of damage estimates through modeling of the accumulation effect of chronic exposure to air pollution. The methods we have developed for estimating impacts are based on the same rich theory and empirical foundation as mitigation costs, and we have now set in place satellite physical accounts for land, energy resources, and population (Asadoorian, 2005) so that we can dynamically link this theoretically based economic model with earth system components.
Asadoorian, M. O. 2005. Simulating the Spatial Distribution of Population and Emissions to 2100. MIT Joint Program for the Science and Policy of Global Change Report No. 123, Cambridge, MA.
Babiker, M., G. Metcalf, and J. Reilly. 2003a. Tax distortions and global climate policy. Journal of Economic and Environmental Management 46:269-287.
Babiker, M., L. Viguier, J. Reilly, A. D. Ellerman, and P. Criqui. 2003b. The welfare costs of hybrid carbon policies in the European Union. Environmental Modeling and Assessment 8:187-197.
Babiker, M., J. Reilly, and L. Viguier. 2004. Is emissions trading always beneficial. Energy Journal 25(2):33-56.
Felzer, B., J. Reilly, J. Melillo, D. Kicklighter, M. Sarofim, C. Wang, R. Prinn, and Q. Zhuang. 2005. Future effects of ozone on carbon sequestration and climate change policy using a global biogeochemical model. Climatic Change 73:345-373.
Hyman, R. C., J. M. Reilly, M. H. Babiker, A. De Masin, and H. D. Jacoby. 2003. Modeling non-CO2 greenhouse gas abatement. Environmental Modeling and Assessment 8:175-186.
Jacoby, H. D., J. Reilly, and J. R. McFarland. 2006. Technology and technical change in the MIT EPPA model. Energy Economics 28(5-6):610-631.
Matus, K. 2005. Health Impacts from Urban Air Pollution in China: The Burden to the Economy and the Benefits of Policy. Master’s thesis, MIT.
Matus, K., T. Yang, S. Paltsev, and J. Reilly. 2006. Economic benefits of air pollution regulation in the USA: An integrated approach. Climatic Change (in press).
McFarland, J., J. Reilly, and H. J. Herzog. 2004. Representing energy technologies in top-down economic models using bottom-up information. Energy Economics 26:685-707.
Metcalf, G., M. Babiker, and J. Reilly. 2004. A note on weak double dividends. Topics in Economic Analysis & Policy 4(1): Article 2.
Otto, V. M., A. Löschel, and J. Reilly. 2006. Directed Technical Change and Climate Policy. MIT Joint Program for the Science and Policy of Global Change Report No. 134, Cambridge, MA.
Paltsev, S., J. M. Reilly, H. D. Jacoby, and K. H. Tay. 2004. The Cost of Kyoto Protocol Targets: The Case of Japan. MIT Joint Program for the Science and Policy of Global Change Report No. 112, Cambridge, MA.
Paltsev, S., J. M. Reilly, H. D. Jacoby, R. S. Eckaus, J. McFarland, M. Sarofim, M. Asadoorian, and M. Babiker. 2005a. The MIT Emissions Prediction and Policy Analysis (EPPA) Model: Version 4. MIT Joint Program for the Science and Policy of Global Change Report No. 125, Cambridge, MA.
Paltsev, S., H. Jacoby, J. Reilly, L. Viguier, and M. Babiker. 2005b. Modeling the transport sector: The role of existing fuel taxes. In: Energy and Environment, R. Loulou, J-P. Waaub, and G. Zaccour, eds. Springer, New York: 211-238.
Prinn, R. G. 2007. Ecosystem-climate feedbacks studied with an integrated global system model. Pp. 97-99 in Understanding and Responding to Multiple Environmental Stresses. Washington, D.C.: The National Academies Press.
Prinn, R., J. Reilly, M. Sarofim, C. Wang, and B. Felzer. 2006. Effects of air pollution control on climate. In: Integrated Assessment of Human-Induced Climate Change. M. Schlesinger, ed. Cambridge University Press (in press).
Reilly, J., and K. Richards. 1993. An economic interpretation of the trace gas index issue. Environmental and Resource Economics 3:41-61.
Reilly, J., R. Prinn, J. Harnisch, J. Fitzmaurice, H. Jacoby, D. Kicklighter, J. Melillo, P. Stone, A. Sokolov, and C. Wang. 1999. Multigas assessment of the Kyoto protocol. Nature 401:549-555.
Reilly, J., M. Babiker, and M. Mayer. 2001. Comparing Greenhouse Gases. MIT Joint Program on the Science and Policy of Global Change. Report No. 77, Cambridge, MA.
Reilly, J. M., H. D. Jacoby, and R. G. Prinn. 2003. Multi-Gas Contributors to Global Climate Change. Arlington, VA: Pew Center on Global Climate Change.
Reilly, J., B. Felzer, S. Paltsev, J. Melillo, R. Prinn, C. Wang, A. Sokolov, and X. Wang. 2004. TheThe economic impact of climate, CO2, and tropospheric ozone on crop yields in China, the US, and Europe. EOS Abstract 7314; B33A-0239.
Reilly, J., S. Paltsev, B. Felzer, X. Wang, D. Kicklighter, J. Melillo, R. Prinn, M. Sarofim, A. Sokolov, and C. Wang. 2006. Global economic effects of changes in crops, pasture, and forests due toGlobal economic effects of changes in crops, pasture, and forests due to changing climate, carbon dioxide, and ozone. Energy Policy (in press).
Sarofim, M., C. E. Forest, D. M. Reiner, and J. M. Reilly. 2005. Stabilization and global climate policy. Global and Planetary Change 47:266-272.
Schafer, A., and H. D. Jacoby. 2003. Technology detail in a multi-sector CGE model: Transport under climate policy. Energy Economics 27(1):1-24.
Sokolov, A. P., C. A. Schlosser, S. Dutkiewicz, S. Paltsev, D. W. Kicklighter, H. D. Jacoby, R. G. Prinn, C. E. Forest, J. Reilly, C. Wang, B. Felzer, M. C. Sarofim, J. Scott, P. H. Stone, J. M. Melillo, and J. Cohen. 2005. The MIT Integrated Global System Model (IGSM) Version 2: Model Description and Baseline Evaluation. MIT Joint Program for the Science and Policy of Global Change Report No. 124, Cambridge, MA.
Sue Wing, I. 2003. Induced Technical Change and the Cost of Climate Policy. MIT Joint Program for the Science and Policy of Global Change Report No. 102. Cambridge, MA.
Yang, T., J. Reilly, and S. Paltsev. 2005. Air pollution health effects: Toward an integrated assessment. Pp. 267-293 in Coupling Climate and Economic Dynamics, A. Haurie and L. Viguier, eds. Berlin: Kluwer Publishers.
CLIMATE CHANGE, MULTIPLE STRESSES, AND AGRICULTURE: WHEN ALL ELSE IS NOT EQUAL
William E. Easterling
Pennsylvania State University
Scientific understanding of how agricultural systems respond to rapid social and environmental change has largely been obtained using research approaches that focus on individual stresses or forcings (e.g., air pollution, climate variability and change, pests and pathogens, loss of genetic diversity, desertification, and land degradation) most often in isolation from one another. Interactions among such stresses are poorly studied, even within integrated assessment modeling frameworks. When focusing on a single stressor, assumptions that all else is equal are the convention.
Agricultural ecosystems currently feed a population of just over 6 billion people, providing enough food for the average global citizen to consume 2,790 calories per day. One of the great human achievements of the 20th century was the steady increase in global agricultural production due to the expansion of cropped land by mechanization plus crop varietal improvements, better plant nutrition, effective pest management, and other technological advances that increased productivity. When asked to feed a growing global population, the world’s farmers and their supporting institutions responded effectively. Even more remarkable was that this increase in production occurred in the face of multiple environmental and social stresses on the food system, including widespread climate variability—prolonged droughts, severe floods, and heat waves—and likely the early stages of climate change, pest and pathogen outbreaks, loss of genetic diversity in agroecosystems, desertification and land degradation, water scarcity, war, epidemics, increasing income divides between rich and poor, government mismanagement, and global population growth, to name a few. But the news is not all good as there have been notable regional failures and there are reasons for concern looking into the future. In this abstract I review recent trends and future projections of global agricultural production and then consider how multiple stresses may alter those projections. Thesholds and nonlinearities, where they are known, are identified, and research gaps and opportunities are mentioned.
One of the greatest stresses on global agriculture has been the historic rise in population and per capita income, both of which constitute the principal determinants of global food demand. Global food demand governs the scale at which the world’s farmers must produce in order to maintain healthy and productive lifestyles of all people. This stress will continue into the future, although there is reason for optimism. Recent revised United Nations population projections to 2050 anticipate that the deceleration of world population growth may be even faster than previously thought. The most recent Medium Variant projection for the world population in 2050 has been revised down to 9.1 billion from its previ-
ous projection of 9.3 billion. The slowing population growth—1.6 percent p.a. today versus 0.6 percent p.a. for 2050—combined with a growing percentage of the world population reaching adequate levels of nutrition (due to increasing per capita income, especially in developing countries), leads to a gradual slowing down of growth in world demand for food and, correspondingly, in world production required to meet demand.
Recent estimates by the Food and Agriculture Organization project annual growth in world agricultural production to decline from 1.6 percent in 2000-2015 to 1.3 percent in 2015-2030 and 0.8 percent in 2030-2050 due to slowing growth in world agricultural demand. This still implies a roughly 55 percent increase in world production by 2030 compared to current production. These projections assume that in the developing countries (where almost all global land expansion takes place, mainly in sub-Saharan Africa and Latin America) another 185 million ha of arable land (+19 percent) will be brought into production between now and 2050 and another 60 million ha of irrigated land (+30 percent). Average cereal yields in the developing countries would have to rise from 2.7 tonnes/ha now to 3.8 tonnes/ha by 2050.
No clear picture of how climate change is likely to alter the above assessment has emerged in the literature. The preponderance of global agricultural studies suggest that climate change is likely to diminish global agricultural capacity by only a few percent if at all by 2050 when taking into account regions that may benefit (i.e., North America, Europe) and regions that may suffer (i.e., the tropics). Any losses would be on top of substantial gains in world output as noted above. A small suite of modeling studies predict that world crop (real) prices are likely to continue to decline through the first two to three degrees C of warming before rising with additional warming (IPCC TAR, 2001/5)—hence, two to three degrees of warming appears to be a crucial threshold for crop prices.
While the global situation looks manageable, there are several reasons for concern at regional levels. Several stresses on agricultural production systems are impeding the achievement of regional food security, especially in the developing world. Sub-Saharan Africa is a case in point that is worth a closer look. It is a region in which stresses on food security occur across several levels of scale. Table 1 lists some examples of major stresses on sub-Saharan Africa that operate at global and regional/local levels.
Agricultural stressors in sub-Saharan Africa operating at the global scale include climate change and widening agricultural trade deficits. Tropical cropping systems have been shown to be vulnerable to even the slightest increase in temperatures because, for most of the major food crops being grown there, mean maximum temperatures are already at the high end of effective photosynthetic temperatures. Modeling studies project tropical crop yields (rice, maize) to fall markedly with only a one degree warming, even when CO2 fertilization is considered—such is a critical threshold. In addition, most of the nations of sub-Saharan Africa became net food importers in the early 1980s and are expected to see their
TABLE 1 Stressors on Sub-Saharan Africa Food Security
Local and Regional
agricultural trade deficit quadruple by 2030. This has inhibited the development of the agriculture sector in the region and limited agricultural income growth, which is a major driver of development.
Agricultural stressors in sub-Saharan Africa operating at regional to local scales include a number of social and environmental challenges. Food production across most of Africa has not kept up with rapid population growth. The population of sub-Saharan Africa is currently growing at a rate of 2.6 percent p.a. and is expected to grow at 2.2-2.6 percent p.a. out to 2030, which is more than double the world average. Sub-Saharan Africa is the only region of the world where per capita food consumption not only remained below acceptable levels (less than 2200 Kcal/day), but has fallen in the last two decades. The effect of emerging infectious diseases such as HIV/AIDS on population growth will be minimal, but their effect on agricultural productivity could be catastrophic. The U.S. Census Bureau estimates that over 40 percent of the reproductive-age population in South Africa is HIV-positive. FAO projects that 20 percent of South Africa’s agricultural labor force will have been lost to HIV/AIDS over the period 1985-2020. This epidemic strikes a population that has generally poor levels of public health and inadequate access to safe drinking water, which are stresses by themselves. On top of these demographic and public health stresses, sub-Saharan Africa experiences widespread political instability and civil strife that has particularly interrupted the distribution of food to people who need it most.
Several environmental problems will continue to stress the sub-Saharan food production system. Southern Africa experienced protracted droughts throughout the 1990s and is considered to be in a dry period relative to the longer-term historical record. Again, no clear picture has emerged as to how the frequency and intensity of droughts may be changed by climate change across sub-Saharan Africa. The degradation of land resources by agriculture becomes a major feedback limiting future agricultural productivity due to deterioration of the land resource base. This is problematic throughout sub-Saharan Africa. Processes at work include salinization of irrigated areas, overextraction of groundwater, chem-
ical depletion of soils, water saturation, leaching of nitrate into water bodies (pollution, eutrophication), off-site deposition of soil erosion sediment, and enhanced risks of flooding following conversions of wetlands to cropping. There is a great deal of debate over how much land degradation has affected crop productivity. Some estimates suggest that land degradation has reduced crop productivity by 25 percent in Africa since World War II.
How the many stresses listed above fit together in determining the vulnerability and resiliency of sub-Saharan agriculture is not known with any certainty. The same can be said virtually anywhere else in the world. Environmental stressors surely interact strongly with social and economic stressors. A drought may substantially reduce crop yields, but temporary crop price increases brought on by production disruptions may offset the stress to farmers, although the consumer pays more. Major gaps exist in understanding how multiple stresses on agriculture and food security interact. The following list details some potential priorities that might help address these gaps:
Compilation of datasets on agriculture and food-related stresses using GIS technology—data should be scalable and easily assembled in different geographic units and time scales
Improvement in basic understanding of how multiple stresses interact to influence important quantities, such as crop yields, public health, regional and per capita income, and the like—special attention should be paid to identifying nonlinearities and thresholds
Development of modeling methodologies in which interactions between multiple stressors (social and environmental) are explicit
Design and implementation of comprehensive food system monitoring capabilities leveraging the success of the U.S. Agency for International Development’s Famine Early Warning System
Improvement in basic understanding of the resiliency of agricultural systems in the face of not one but several stresses occurring simultaneously, especially the identification of system redundancies and other coping strategies
William E. Easterling is the director of the Penn State Institutes of the Environment and professor of geography with a courtesy appointment in agronomy at the Pennsylvania State University. Dr. Easterling’s research interests include the potential for agriculture in developed and developing countries to adapt to climate variability and change; the role of scale in understanding the vulnerability of complex systems; how land use change may influence the uptake and release of carbon in the terrestrial biosphere; the use of experimental long-term climate forecasts to assist decision making under conditions of uncertainty; and the development of methodologies for detecting the impacts of observed 20th-century climate change on natural and managed ecosystems. Dr. Easterling received his Ph.D. in geography from the University of North Carolina at Chapel Hill.
SOCIOECONOMIC IMPACTS OF MULTIPLE STRESSES ON CITIES
Patricia Romero Lankao
Autonomous Metropolitan University, Xochimilco
Four issues require attention when analyzing the socioeconomic impacts of multiple stresses on cities when reflecting on possible adaptive strategies: (1) weight of path dependency, (2) importance of scale, (3) usefulness of existing analytic tools, and (4) role of institutions. All will be described in terms of what has been learned, which research gaps still exist, and how understanding multiple stresses might affect the conduct of future research, assessments, and decision making.
DEVELOPMENT PATHWAYS: KEY LINK BETWEEN MULTIPLE STRESSES AND DRIVERS?
Many of the forces behind emissions trajectories and land use changes induced by urban areas, such as economic growth, technological transformations, demographic shifts, and governance structures, are similar or even the same to those underlying diverse pathways of development, explaining in part why
industrialized countries and the wealthy in the South account for the highest share of atmospheric emissions, and have much higher ecological footprints (e.g., land use changes induced by cities’ demands on wood) than poor countries, regions, and sectors. Rees and Wackernagel (1996) have documented the influences and effects of world cities, such as Amsterdam in distant places (“teleconnections”). Another example is the demand for meat in Mexico City, which led in the 1950s and 1960s to land cover changes in Tabasco 400 km away (Barkin et al., 1978).
some regions and sectors, especially from the developing world, are more vulnerable to impacts such as climate variability and change than others. The poor in urban areas for example lack access to climate-controlled shelters; they already face environmental problems (sanitation, deficiencies in the operation of public services, location in risk-prone areas); they suffer malnutrition, poor housing conditions, and low income. All those conditions that have been further worsened by structural adjustment programs implemented during the last two decades may produce a highly segregated urban space and contribute to aggravate—especially for the poor—the negative impacts of changes in biophysical processes in urban areas.
If the impacts of changes in atmospheric composition go beyond a certain threshold and/or urban areas are not prepared to deal with that level of impact,
then cities from both the developed and the developing world may become vulnerable. Consider the 2003 heat wave in Europe as example of an event a developed country like France was vulnerable to. This did not necessarily result from lack of resources. But it rather related not only to health conditions and health services for the elderly people, but also to social conditions and organization (i.e., to inadequate climate conditioning in buildings; to the fact that the elderly people were alone while their families were on vacation). Think about environmental change’s possible impacts on the pool of resources and ecosystems an urban area relies on. As some scenarios foresee, climate change will strongly affect already stressed watersheds in both the developing world (e.g., Lerma and Cutzamala for Mexico City) and the developed world (Colorado River for Southern California).
The problem is that most scholars tend to focus either on some drivers of emissions trajectories (e.g., IPCC’s Work Group III) or on the vulnerability or impact to multiple stresses (e.g., IPCC’s Work Group II using vulnerability assessments). And knowledge would advance faster if both groups could explore and model the complex linkages between drivers of development pathways and stressors facing urban sectors and localities. Consider another example. Market forces and the declining role of the state as urban planner are key drivers of urban growth in risk-prone areas of developing countries and even of industrialized countries—as New Orleans has recently shown us. The retrenchment of the state in its role as regulator usually appears as one of the multiple stresses facing urban dwellers. Wouldn’t it be better to explore how market forces and other drivers relate or cascade with other and multiple stresses to produce certain vulnerabilities/adaptive capacities? Isn’t it a challenge to develop an integrated perspective to understand the pathways through which socioeconomic, institutional, and environmental processes influence livelihoods, economic activities, urban life, migration, and other realms where adaptive capacity takes place in urban areas?
RELEVANCE OF SCALE
Scale is important in diverse and not yet fully explored ways when assessing the socioeconomic impacts of changes in atmospheric composition and dynamics.
First, the referred changes are but a part of a set of multiple stresses operating at diverse scales in space and through time (e.g., markets, deficiencies in housing, or in the supply and operation of urban services, infrastructure, sanitation, and health). The problem is that research on this issue is in its infancy. We need to better understand—and if possible model—the global and regional socioeconomic, geopolitical, and environmental processes affecting the vulnerability of urban systems.
Second, both the exposure to and the distribution of urban groups and localities sensitive to the impacts of changes in atmospheric composition and dynamics vary greatly across scale. The primary social and economic conditions that influence adaptive capacity (e.g., access to financial resources or to governmental relief) also differ with scale. One could say, for instance, that at a national scale cities in industrialized countries such as Norway or the United States can cope with most kinds of gradual environmental changes, but focusing on more localized differences (between New York and New Orleans for instance) can show considerable variability in stresses and capacities to adapt. This is another area where more research is needed.
Third, temporal scale is a critical determinant of the capacity of urban systems to adapt to environmental changes. The history of the city—path dependency—will determine the diversity and complexity of its population’s current and future adaptive capacity. Of course, rapid changes or abrupt changes (e.g., flooding, droughts) are more difficult to absorb without painful costs than gradual change. But gradual change can accumulate until urban areas reach a threshold in which their adaptive capacity is no longer feasible. Consider how slow changes in the length and frequency of seasons could affect water supplies in cities, or how slow changes in temperature and humidity could affect the livelihood of urban people. These issues have received little attention so far.
Rather than using one-dimensional perspectives to understand the responses of urban areas to the impacts of changes in the composition of the atmosphere, we need broader multidimensional and multiscale approaches. This is a challenge indeed. Examples of such tools and concepts that will be described in this section are the Kaya identity, vulnerability/adaptation assessments, livelihoods, and tolerable windows approach. According to the IPAT identity, environmental impact is the product of the level of population combined with affluence (e.g., measured by income per capita) and the level of technology (e.g., measured by emissions per unit of income). Numerous articles use this kind of identity to analyze the drivers of CO2 emissions (Kaneko and Matsouka, 2003), often referring to it as the “Kaya identity,” according to which:2
The Kaya identity has the advantage of being simple and allowing for “some standardization in the comparison” and analysis of diverse emissions trajectories (Nakicenovic, 2004). Clearly, it is a very general way of looking at emissions; for example, it assumes that each variable enters linearly and independently, which is surely not the case, and it omits other factors (such as institutional ones) as emissions drivers that are left as residual of the equation if looking at past emissions evolution (IPCC, 2000; Nakicenovic, 2004). The identity is broadly used to construct scenarios; it helps to identify proximate but not ultimate drivers, but it fails to identify many key drivers—e.g., government regulation, social organization, and economic organization, as well as public perceptions, which influence patterns of technologies in use affecting trajectories of greenhouse gases and other atmospheric releases.3 The question is whether a similar equation in which the variables do not enter independently could be applied to the analysis of multiple stresses, whether such an equation could at least allow for some standardization in the comparison of diverse cases.
Rather than selecting a particular environmental stress of concern and trying to identify its consequences as impact assessment does, vulnerability/adaptation assessments:
Choose a group or unit of concern (e.g., informal or wealthy settlements, poor or rich urban dwellers).
Try to evaluate the risk of specific adverse outcomes for that unit when confronted with a set of stresses (e.g., climate variability and change, new patterns of foreign direct investment and of industrial location, and structural adjustment programs). Note that all these stresses redefine the economic base of urban areas, drive new territorial patterns of urban growth and new emissions trajectories (Romero Lankao et al., 2005); at the same time they define a new physiognomy and geography of vulnerable groups and localities within the cities.
Seek to identify a set of factors (e.g., institutions, assets, social capital) that may reduce or to the contrary enhance adaptation to those stressors.
Precisely because vulnerability assessments concentrate on exposure units, they assume that vulnerability is highly dependent on scale and context. This has two consequences we should address in our workshop. Assessments focusing on a narrow range of scales will miss most of the importance for societal efforts to cope with the impacts of changes in the atmosphere. It is therefore essential for
vulnerability assessments to address multiple drivers and stresses that interact across a variety of scales.
One tool is under development within the IPCC community and intends to deal with the future: the tolerable windows approach. This tool selects an exposure unit and classifies the potential outcomes either as acceptable or adverse. The next step is to try to define the dynamic combination of environmental and socioeconomic and institutional stresses that could result in negative outcomes. For this it is necessary to develop scenarios of the future that include not only environmental stresses but also socioeconomic stresses (Toth, 2001).
Livelihood analysis is another multidimensional concept applied to both rural and urban studies. It pays attention to the way in which a living is obtained and gives especial consideration to agency. Livelihood analysis comprises “the capabilities, assets (stores, resources, claims, and access) and activities required for a means of living” (Ellis, 2000). The tool is useful to study how individuals, households, and communities in cities adapt to the impacts of changes in the composition of the atmosphere. It pays attention to the social, economic, institutional, and environmental dimensions of adaptation strategies by those agents; it explores how those dimensions interact at different scales. This tool can offer insights to design policies aimed at both enhancing adaptation to the impacts of atmospheric changes and reshaping the socioeconomic impacts of existing urban development pathways.
I would like to close this paper with one citation and some thoughts on the role of institutions in adapting to the impacts of changes in the composition of the atmosphere. According to Steffen et al. (2003):
The current states of vulnerability research and vulnerability assessment exhibit both the potential for substantial synergy in addressing global environmental risks … as well as significant weaknesses which undermine that potential. A substantial base of fundamental knowledge has been created. However it is highly fragmentary in nature, with competing paradigms, conflicting theory, empirical results often idiosyncratic and tied to particular approaches, and a lack of comparative analysis and findings.
My guess is that one research path for us is to develop meta-analytic tools to tease out the paradigms behind those approaches and to see whether and, if so, at which levels it is possible to make those analyses and their findings comparable.
Last but not least, institutions play a significant role both as drivers/stressors (IDGEC, 2005; Romero Lankao et al., 2005) and as enhancers of urban systems’ ability to cope with and adapt to the negative impacts of changes in atmospheric
composition and land use (IDGEC, 2005). As already mentioned in this paper the first task we are confronted with is to understand within an integrated perspective the pathways through which institutions together with other socioeconomic and environmental processes influence livelihoods, economic activities, urban life, migration, and other realms where adaptive capacity takes place in cities. The second and more difficult task is to consider existing research on the science policy interface, which may help us understand
why and how decision makers relate to scientific information and findings on socioeconomic and institutional impacts of changes in land use and in atmospheric composition;
the resources and institutional capacity decision makers have to design and implement adaptation strategies;
the role of other organizations, institutions, and stakeholders in the design and implementation of adaptation strategies.
Barkin, D., con la colaboración de Adriana Zavala. 1978. Desarrollo regional y reorganización Campesina: La Chontalpa como reflejo del problema agropecuraio mexicano. Mexico: Editorial Nueva Imagen.
Bruchner, T., G. Petschel-Held, F. L. Tóth, H.-M. Füssel, C. Helm, M. Leimbach, and H.-J. Schellnguber. 1999. Climate change decision-support and the tolerable windows approach. Environmental Modeling and Assessment 4:217-234.
Ellis, F. 2000. Rural Livelihood and Diversity in Developing Countries. Oxford: Oxford University Press.
Kaneko T., and Y. Matsouka. 2003. Driving forces behind the stagnancy of China’s energy related CO2 emissions from 1996-1999: The relative importance of structural change, intensity change and scale change. Draft
Nakicenovic, N. 2004. Socioeconomic driving forces of emission scenarios. Pp. 225-239 in The Global Carbon Cycle: Integrating Humans, Climate and the Natural World, C. B. Field and M. R. Raupach, eds. Washington, D.C.: Island Press.
Rees, W., and M. Wackernagel. 1996. Urban ecological footprints: Why cities can not be sustainable—and why they are a key to sustainability. Environmental Impact Assessment Review 16:223-248.
Romero Lankao, P., H. López Villafranco, A. Rosas Huerta, G. Günther, and Z. Correa Armenta, eds. 2005. Can Cities Reduce Global Warming? Urban Development and the Carbon Cycle in Latin America. México, IAI, UAM-X, IHDP, GCP. 92 pp.
Steffen, W., A. Sanderson, P. D. Tyson, J. Jäger, P. A. Matson, B. Moore III, F. Oldfield, K. Richardson, J. Schellnhuber, B. L. Turner II, and R. J. Wasson. 2004. Global Change and the Earth System: A Planet Under Pressure. Berlin, Heidelberg, New York: Springer-Verlag.
Dr. Patricia Romero Lankao is a professor in the Department of Politics and Culture at the Autonomous Metropolitan University, Campus Xochimilco, in Mexico City, Mexico. Her general field of expertise and interest is in the interface of the human dimensions of global environmental change. She has published on
issues such as the design of Mexican environmental policy, water policy in Mexico City, environmental perceptions and attitudes toward public environmental strategies and instruments, and vulnerability to climate variability and change among farmers and water users. Dr. Romero, a sociologist by training, has two doctoral degrees, one in regional development from the Autonomous Metropolitan University and one in agricultural sciences from the University of Bonn, Germany.
UNDERSTANDING VULNERABILITY OF ECOSYSTEM GOODS AND SERVICES AND RESPONSE STRATEGIES
Richard B. Norgaard
University of California, Berkeley
Questions suggested: (1) What has been the economic impact of large-scale stresses to ecosystems, and how has this impact been characterized? (2) How is vulnerability of ecosystem goods and services characterized? (3) How best can society value ecosystems and ecosystem goods and services to effectively prepare for the impact of multiple stresses?
It is important to approach these questions from a dynamic systems perspective within which environmental and socioeconomic systems are interacting over time, each affecting the other. Economic impacts are not simply “there” to be identified by the economist but rather are a product of prior conditions. Thus the economic impact of large-scale or multiple stresses is very dependent on how well we are prepared for and how well we respond to the stresses. Hurricane Katrina laid bare the human and economic costs of being ill prepared and unresponsive. The critical point here is that a particular stress, or particular combination of stresses, does not map to a particular economic impact. Between a stress and an impact there are typically human-modified environments, technological systems, and socioeconomic institutions and capabilities whose states and hence responses to stresses depend on both preceding stresses and human decisions to recognize, develop, and protect environmental qualities, technological capacities, and institutional capabilities.
Thus the economic implications of an extended drought in the Midwest that seriously jeopardized corn, soybean, and wheat production depends on the existence, or not, of the agroecological, technological, and socioeconomic conditions necessary to raise alternative grains that are quite normally grown, for example, in arid regions of India. The definition of a drought (i.e., is there enough water?) is not simply a matter of the difference between rainfall and crop needs, or between soil storage, rainfall, and evapotransporation. Need, evapotransporation, and soil storage depend on the crops grown.
As we saw in the case of Katrina, the distribution of income can also critically affect the impacts observed. The human toll of an extended drought in the Midwest could be no more than the discomfort of foregoing beef and eating soy burgers. During the stress of World War II, margarine became a normal food in the American diet through programs that restricted the availability of butter for all. But if the rich continue to eat beef through a drought, the price of grains could quickly become a major hardship on the poor.
Similarly, there are scalar issues associated with risk that are critical. Historically, near-subsistence farmers planted a variety of crops in the expectation that some of them would fit the weather conditions of a particular year. With trade and specialization, risks and risk reduction strategies become distributed more globally. Thus, low corn, soybean, and wheat yields in the United States in any particular year or decade are dampened by global production unless, as is possible with climate change, much of the globe is affected in the same period. A rapid transition in climate conditions could also occur globally such that globalizing risk becomes a less effective strategy.
We should be as concerned about combinations of social and environmental stresses as about combinations of environmental stresses. It was much more difficult to be prepared for and to respond to the combination of stresses known as the “dust bowl” during the Great Depression because the social system was already highly stressed by a dysfunctional economy. No doubt environmental stresses during World Wars I and II also resulted in greater hardship because social system resources were devoted to the wars. It is also important to keep in mind that the social conditions, specifically the movement of soldiers and material at the end of World War I, helped spread the Spanish Flu virus, which ended up killing 10 times as many Americans as the Great War.
We have a tendency to think of fair to good socioeconomic times as normal and bad as the exception, but surely 20 percent of the years in the United States during the 20th century were pretty bad. And just as surely, 20 percent of the world’s population at any one time is engaged in a civil or regional war or having bad economic times. Yet most of our scenarios for “sustainable development” are built around fair to good times being an uninterrupted norm.
Acknowledging the dynamic interactions between social and environmental systems has not yet led to the incorporation of appropriate models to address periodic stresses in environmental assessments, let alone combinations of stresses. Efforts to date to portray the interactions between social systems and environmental systems in assessments tend to forecast alternative smooth scenarios. For example, the assessments by the Intergovernmental Panel on Climate Change are tied to alternative scenarios that differ, for example, by overall rates of growth, types of technology, and differences between industrialized and less industrialized countries, but these scenarios play out without discontinuities. The scenarios of the Millennium Ecosystem Assessment are more heuristic and the differences between them with respect to resilience overall, patchiness globally, and protection of the poor to stresses are discussed but not actually quantified.
Valuation of ecosystem services as a technique has also presumed a steady forecast of good times, both environmentally and socially (at least for the rich). Because a dollar of a poor person tends to be counted the same as the dollar of a rich person, ecotourism values, for example, can swamp subsistence ecosystem services important to the poor. Clearly it is these more basic values that are more important to be studying now that we are more concerned about multiple stresses.
In any case, we value what we know, and as the uncertainty of the future becomes more clear to more people, we will value ecosystem services differently. This is rather a circular problem, for we want the values to inform people of the importance of ecosystem services. But to the extent that some of the ways economists derive values flow from an informed public expressing choices, most ecosystem services, especially under conditions of stress, are highly undervalued because people are less aware of the importance of the services than they should be.
Richard B. Norgaard is a professor in the Energy and Resources Program at the University of California, Berkeley. His areas of expertise include environmental epistemology; ecological, environmental, and resource economics; environment and development in less developed countries; development as social system and ecological system coevolution; tropical rain forests; pest management; petroleum development; and water development. His recent research addresses how environmental problems challenge scientific understanding and the policy process, how ecologists and economists understand systems differently, and how globalization affects environmental governance. Dr. Norgaard received his Ph.D. in economics from the University of Chicago.
PATTERNS, SOURCES, AND IMPACTS OF DECADAL-TO-MULTIDECADAL CLIMATE VARIABILITY IN THE WEST
Julio L. Betancourt4
U.S. Geological Survey Desert Laboratory
Both instrumental and tree-ring records show that the western U.S. climate exhibits low-frequency modes in the form of persistent and widespread droughts that alternate with pluvials. Some notable examples are the dry Medieval period (A.D. 900-1300) and the ensuing wetter Little Ice Age (A.D. 1400-1850); the dramatic switch from the megadrought in the late 1500s to the megapluvial in the early 1600s; and the bracketing of epic droughts in the 1930s and 1950s by two of the wettest periods (1905-1920 and 1965-1995) in the last millennium. Such decadal-to-multidecadal (D2M) hydroclimatic variability is assumed to operate through the oceans and clearly can occur independent from anthropogenic forcing. Statistical and modeling studies show teleconnections to low-frequency SST variability in the Pacific, Indian, and North Atlantic Oceans, and there is mounting interest in both mechanisms and predictability.
D2M precipitation variability in the western United States tends to be spatially coherent and can synchronize physical and biological processes in ways that are complex and difficult to forecast and monitor. D2M variability can synchronize fluctuations in surface water availability across major basins and can thus overextend regional drought relief and interbasin transfer agreements. Traditionally, both water resource and floodplain management in the West have been based mostly on stationary assumptions about surface flow—that the mean and moments of the annual or peak discharge distributions do not change over time. Federal flood insurance relies on the concept of the 100-year flood, which is calculated routinely with flood frequency methods that assume stationarity. And we also assume stationarity in annual operations of critical water resources. For instance, Article III of the Compact apportions 7.5 million acre feet (MAF) per year each to the Upper and Lower Colorado River Basins, stipulates that Upper Basin states cannot deplete the flow at Lees Ferry by more than 75 MAF over a period of 10 consecutive years and mandates a moving 10-year average release of 8.23 MAF/year from Lake Powell into the Lower Basin. In the case of D2M variability, 100 years may not be long enough to evaluate stationary assumptions in water resource planning, and we are forced to rely on tree-ring reconstructions of precipitation and streamflow. These reconstructions vary in coverage and quality, but nonetheless are a good first approximation of the history and long-term probability of D2M precipitation and streamflow regimes. In particular, probability distribution functions from long reconstructions of hydroclimate (precipitation or
streamflow) or climatic index series (AMO, PDO, etc.) can be used to calculate the occurrence and return probabilities of climatic episodes. This information can then be mapped to decisions about annual water resource operations or facilities planning.
By synchronizing ecological disturbances and recruitment pulses, D2M variability also plays a key role in structuring woodland and forest communities in western watersheds. In the event of longer, hotter growing seasons, D2M variability will still determine the timing and pace of ecosystem changes. Oscillations between warm-dry and warm-wet regimes will continue to produce uncommonly large disturbances followed by accelerated regeneration and succession. Such large-scale vegetation changes will have complex hydrological effects and will add further uncertainty to water resource availability. A principal challenge for land managers in the 21st century will be to manage for disturbance and succession in purposeful and systematic ways that promote asynchrony and patchiness at local to regional scales while still preserving goods and services that ecosystems provide.
Julio L. Betancourt is project chief, National Research Program, Water Resources Division, U.S. Geological Survey and adjunct professor in the Departments of Geoscience and Geography at the University of Arizona. The focus of his research is ecosystem and watershed responses to climate variability on different temporal and spatial scales. Dr. Betancourt received his Ph.D. in geosciences from the University of Arizona, Tucson.