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5
Climate and Climate Change Research Entering the Twenty-First Century1

Summary

Climate is variable on time scales of seasons to centuries and over longer time intervals. Both climate variability and climate change can have significant societal impact. Climate influences agricultural yields, water availability and quality, transportation systems, ecosystems, and human health. Climate variability and change are a product of external factors such as the Sun, complex interactions within the Earth system, and anthropogenic effects. The mission of climate research is to understand the physical, chemical, and ecological bases of climate in order to characterize and predict the nature of climate variability from seasonal and interannual to decadal and longer time scales, and to assess the role of human activities in affecting climate and of climate in influencing human activities and environmental resources.

A central goal of climate research is prediction. The objectives are to understand the mechanisms of natural climate variability on time scales of seasons to centuries and to assess their predictability, to predict the future response of the

l Report of the Climate Research Committee: E.J. Barron (Chair), Pennsylvania State University; D. Battisti, University of Washington; R.E. Davis, Scripps Institution of Oceanography; R.E. Dickinson, University of Arizona; T.R. Karl, National Climatic Data Center; J.T. Kiehl, National Center for Atmospheric Research; D.G. Martinson, Lamont-Doherty Earth Observatory of Columbia University; C.L. Parkinson, NASA Goddard Space Flight Center; S.W. Running, University of Montana; E.S. Sarachik, University of Washington; S. Sorooshian, University of Arizona; K.E. Taylor, Lawrence Livermore National Laboratory; P.J. Webster, University of Colorado.



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Page 272 5 Climate and Climate Change Research Entering the Twenty-First Century1 Summary Climate is variable on time scales of seasons to centuries and over longer time intervals. Both climate variability and climate change can have significant societal impact. Climate influences agricultural yields, water availability and quality, transportation systems, ecosystems, and human health. Climate variability and change are a product of external factors such as the Sun, complex interactions within the Earth system, and anthropogenic effects. The mission of climate research is to understand the physical, chemical, and ecological bases of climate in order to characterize and predict the nature of climate variability from seasonal and interannual to decadal and longer time scales, and to assess the role of human activities in affecting climate and of climate in influencing human activities and environmental resources. A central goal of climate research is prediction. The objectives are to understand the mechanisms of natural climate variability on time scales of seasons to centuries and to assess their predictability, to predict the future response of the l Report of the Climate Research Committee: E.J. Barron (Chair), Pennsylvania State University; D. Battisti, University of Washington; R.E. Davis, Scripps Institution of Oceanography; R.E. Dickinson, University of Arizona; T.R. Karl, National Climatic Data Center; J.T. Kiehl, National Center for Atmospheric Research; D.G. Martinson, Lamont-Doherty Earth Observatory of Columbia University; C.L. Parkinson, NASA Goddard Space Flight Center; S.W. Running, University of Montana; E.S. Sarachik, University of Washington; S. Sorooshian, University of Arizona; K.E. Taylor, Lawrence Livermore National Laboratory; P.J. Webster, University of Colorado.

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Page 273 climate system to human activities, and to develop improved capabilities for applying and evaluating these predictions. The climate research of the past few decades drives the requirements for future research by focusing our attention on the remaining uncertainties and on the importance of climatic research for society: • Climate variability, such as El Niño, can be characterized by significant economic and human dislocations. Modeling studies over the past two decades suggest that aspects of this climate variability may be predictable. In cases where El Niño/Southern Oscillation (ENSO) events were predicted in advance, immediate practical benefits were realized through human response and adaptation. • Analyses of historical records have revealed a number of interesting cases of longer-period fluctuations for North America and other parts of the world, while model studies have demonstrated that ocean-atmosphere and land-bio-sphere-atmosphere interactions are plausible mechanisms to explain decade-to-century variability. Historical and paleoclimatic data, as well as coupled models, indicate the potential for significant climate variability on long time scales. Such changes can be expected to occur in the future, irrespective of human impacts on climate. Current observational capabilities and practice are inadequate to characterize many of the changes in global and regional climate. An enhancement of current observational capability and improved knowledge of the coupled Earth system will therefore likely increase our understanding of climate variability on all time scales and lead to a greater realization of practical benefits. • The effort to predict the climate response to increases in greenhouse gases has both demonstrated the importance of this problem to society and focused attention on many of the most important limitations of current climate models. Increased concentrations of greenhouse gases and changes in land use and land cover are directly and indirectly tied to human activities. Current model projections based on increases in greenhouse gases and aerosols and on land cover change indicate the potential for large, and rapid, climate change relative to the historical and paleoclimatic records, with concomitantly large influences on human activities and ecosystems. Although remarkable progress in developing these climate models has occurred over the past two decades, current climate models are characterized by a great number of uncertainties. Improved predictive capability is likely to have a positive impact on economic vitality and national security because of its potential to minimize risk and maximize benefit associated with the impacts of any climate change. A comprehensive analysis of the remaining scientific questions and uncertainties and of the societal drivers for climate research leads us to four major imperatives for the twenty-first century. Each imperative is associated with a series of basic requirements:

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Page 274 1. We must work to enhance current observational capabilities and to build a permanent climate observing system. • Where feasible, adopt consistent data collection and management rules to ensure the utility of operational and research system measurements for climate research. • Develop and adopt interagency plans to ensure the protection of critical long-term observations, to limit gaps in continuity due to small budget changes in single agencies, and to recognize the value of these observations in a balanced, integrated research program. • Provide strong U.S. support and participation in the development of a global climate observing system (GCOS). • Ensure full and open international exchange of data and information. • Maintain major research observation systems, such as the Tropical Ocean Global Atmosphere (TOGA) Tropical Atmosphere Ocean (TAO) array, that have demonstrated clear predictive value. • Focus on key opportunities for reducing major uncertainties in climate models, including improved observations of water vapor. • Ensure full interagency commitment to both the in situ and the satellite observations necessary to address the major uncertainties in our understanding of the climate system, including a commitment to long-term Earth observations of critical variables such as the major climatic forcing factors. 2. We must extend the instrumented climate record through the development of integrated historical and proxy data sets. • Widely sample the alpine glaciers and ice caps before this important repository of information on natural variability is lost. • Continue efforts to collect and analyze data from around the world from tree rings, lake sediments, corals, and ice cores, and actively pursue high-resolution records from ocean sediments. • Focus research efforts on the development and validation of proxy indicators. 3. We must continue and expand diagnostic efforts and process study research to elucidate key climate variability and change processes. • Enhance cross-disciplinary communication and collaboration. • Develop clearly articulated linkages between strategies for observation, analysis, model development, and application of predictions to evaluating consequences of climate change. • Implement focused research initiatives on processes and in regions that are identified as important in understanding variability in the climate system. • Implement and analyze new observations necessary for understanding the

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Page 275 processes that couple the components of the Earth system and improve our understanding of climate variability on decade-to-century time scales. • Develop focused process studies with the objective of addressing key uncertainties associated with boundary layer processes and vertical convection; improved linkages coupling the atmosphere, oceans, and land surface; and more explicit representation of land surface processes, including vegetation and soil characteristics. • Support the development and implementation of a comprehensive research program to study and advance seasonal-to-interannual prediction. Such a program is currently the objectives of GOALS (Global Ocean-Atmosphere-Land System) of the World Climate Research Programme (WCRP). • Support the development and implementation of a comprehensive research program to study the mechanisms of decadal-to-century variability and its implications for longer time-scale predictability. Currently, the planning for this element is incorporated in the Dec-Cen (study of climate variability on decadal-to-century time scales) and anthropogenic climate change components of the WCRP. 4. We must construct and evaluate models that are increasingly comprehensive, incorporating all major components of the climate system. • Improve opportunities and enhance efforts at model observation and model-model comparisons that pay particular attention to simulating observed changes associated with solar irradiance, aerosol loadings, and greenhouse gas concentrations. • Develop mechanisms that promote formal interaction between physical scientists and social scientists, by working on common problems to improve the applications and assessments of climate change impacts. • Enhance the computational infrastructure and focused efforts to develop climate system models that include explicit representation of the atmosphere, ocean, biosphere, and cryosphere. • Focus on key opportunities for reducing major uncertainties in climate models, including greater understanding of climate-water vapor feedbacks and improved representation of atmospheric chemistry and indirect chemistry-climate interactions. • Focus effort on improving the credibility and usefulness of climate model predictions at spatial scales relevant to analysis of the responses of ecosystems, socioeconomic systems, and human health to climate change predictions. • Develop and construct high-resolution, regional climate models along with empirical methods for producing estimates of climate change characteristics of immediate relevance to humans. These four imperatives offer a general framework, while the specific objectives and requirements for each characterize more specific opportunities to promote

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Page 276 significant advancement in climate and climate change research. To some, the list of requirements outlined above may appear overly ambitious and without priority. However, a comprehensive climate research program that serves societal needs is clearly within our grasp. In many cases, the programs required to achieve these objectives are in place. In other cases, changes in requirements can be implemented with minimum budgetary impact. In still other cases, objectives can be fulfilled by increased collaboration and closer interagency planning and linkages. However, even some of the more logical, minimal-impact issues appear to be problematic. For example, in terms of the requirement for continuity and quality as part of the climate observing system, current policies verge on becoming a national and international embarrassment. Addressing these issues must be a priority. Finally, with careful planning to achieve greater efficiencies, the full spectrum of climate objectives should be realizable. Although each of the listed requirements has substantial merit, we recognize that improvements and augmentations of the U.S. climate research programs must still be paced, based on budgetary and other considerations. Consequently, the requirements described above are placed in a prioritized framework in the remainder of this Disciplinary Assessment. This prioritized framework is based on a relatively simple perspective. Improvements that have minimal budgetary impact but substantial merit should be implemented without hesitation. Requirements with significant programmatic or budgetary implications should have identifiable levels of priority or clear trade-offs with current efforts. Introduction Three general categories of climate variability and change have been adopted by the World Climate Research Programme: seasonal-to-interannual climate variability, decadal-to-centennial climate variability, and changes in global climate induced by the aggregate of human activities that change both the concentrations of greenhouse gases and aerosols in the atmosphere and the pattern of vegetative land cover. Humans, as individuals and societies, and ecosystems are affected by and respond to each of these three categories of variability and change. Useful predictive skill for seasonal-to-interannual climate variability has been demonstrated. Moreover, early indications of human influence on global climate warming are emerging from the background of natural climate variability. The possibility that human activities have the potential to modify natural climate variability and long-term climate trends on a global scale is a research issue of high priority. Results of such research will have very high utility for informing the public and decision makers of appropriate response strategies. Climate is defined as the long-term statistics that describe the coupled atmosphere-ocean-land weather system, averaged over an appropriate time period. For example, the averaged daily mean, minimum, and maximum temperatures recorded for a given month at a specified place are some important manifesta-

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Page 277 tions of climate. Likewise, the daily average hours of sunlight, cloud cover, rainfall, ground water saturation, snowpack, and runoff observed for a given month at a specified locality are other important climate characteristics. Climate variability refers to fluctuations in climate statistics with reference to a very long time average. Thus, the average summer temperature over a region may differ from year to year (interannual variability) or may manifest a fluctuation that spans a number of years (decadal variability). Natural climate variability has been observed on a range of time scales from months to seasons to centuries and more. A climate trend refers to a long-term secular change in average climate statistics or a change in their statistical variation about the average. A climate trend may be forced by a cause external to the climate system, such as a change in the solar radiative output, or by human-induced changes in the atmospheric composition of trace gases and aerosols or the structure of vegetative land cover. A climate trend may also be forced by an internal change in the climate system, which could result, for example, from a change in ocean circulation patterns. A climate quantity is predictable when a significant fraction of its variations can be consistently explained by a physical theory or mathematical model. Meaningful predictive skill is usually based on correlation between the predicted time series and the verifying time series of the quantity. Since climate statistics are strongly correlated with boundary quantities (e.g., sea surface temperatures), the boundary quantities may be considered climate quantities. Seasonal-to-interannual variability, such as the phases of ENSO, is associated with widely distributed weather anomalies and sometimes severe conditions. These anomalies may persist for many months and can result in significant economic and human dislocations from Australia through tropical and semitropical South America to parts of Africa. Historical records and paleoclimatic data sources indicate the occurrence of significant climate variability on time scales of decades to centuries. Climate variability on these time scales has produced marked shifts in human well-being recorded in history over the past several centuries and can be expected to result in significant economic and human dislocations in the future. Current climate model projections based on anthropogenic increases in greenhouse gases and land cover changes indicate the potential for large, and rapid, climate change relative to the historical and paleoclimatic records, with concomitantly large influences on human activities and ecosystems. Climate change can lead to significant changes in energy use, air pollution, crop yields, water quality and availability, the frequency and intensity of severe weather events, and the occurrence and spread of infectious diseases. Improved knowledge of the climate system offers the potential to enhance our predictive capability, which could support societal efforts to adjust to, forestall, or even eliminate some of the negative impacts of projected climate change. An enhanced capability to predict future climate will have a positive impact on economic vitality and national security.

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Page 278 Progress in understanding the physical, chemical, and ecological bases of climate during the past few decades is clearly a result of a wide variety of research efforts. A clear set of scientific objectives and requirements can be formulated for the coming years. Nonetheless, significant progress in achieving the mission of characterizing and predicting seasonal-to-century time-scale variability in climate, including the role of human activities in forcing this variability, is likely to take a decade or more. Some aspects of the problem will continue to be intractable for considerably longer periods. The remainder of this Disciplinary Assessment articulates a mission and identifies the principal issues and related scientific questions that challenge the climate research community entering the twenty-first century. Seven scientific and programmatic objectives intended to guide this community over the next decade are presented. Mission Statement Human endeavors have come to depend on familiar global and regional environments. In fact, much of the fabric of our society is tied directly to climate through agriculture, water resources, and energy utilization. We have long recognized that climate is variable on time scales of seasons to centuries, and even longer intervals, and that this variability can have significant societal impact. El Niño events, the 1930s drought in the United States, the Sahel droughts, and variations in the monsoons over the most populous areas of the globe provide examples of the importance of natural climate variability for human activities and well-being. The nature of global and regional climates is also subject to change because of human activities, most notably in response to the observed changes in atmospheric composition (e.g., greenhouse gases and aerosols) and land use, characteristic of the last century. The potential impact of these changes is great and spans such diverse issues as agricultural yield, water resource availability, transportation systems, water quality, energy production and utilization, frequency and magnitude of extreme weather events, natural ecosystem viability, and even the nature of infectious diseases and their spread by agents that are influenced by climate. The magnitude and timing of human-induced climate change remain active research topics. Large gaps in our knowledge of interannual and decade-to-century natural variability hinder our ability to provide credible predictive skill or to distinguish the role of human activities from natural variability. Narrowing these uncertainties and applying our understanding define the mission of climate and climate change research and education for the twenty-first century. The mission of climate research is to understand the physical, chemical, and ecological bases of climate in order to characterize and predict the nature of climate variability from seasonal and interannual to decadal

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Page 279 and longer time scales, and to assess the role of human activities in affecting climate and of climate in influencing human activities and environmental resources. The scientific uncertainties, coupled with the potential significance of climate variability and climate change, indicate the importance of developing a scientific strategy for monitoring changes to the climate system, addressing key scientific uncertainties, enhancing our understanding of the impact of human activities, assessing societal vulnerability to climate change, and minimizing risk and maximizing benefits to society. Our primary goal is to enhance our capacity to predict climate variability and climate change, which implies understanding the impact of human activities in influencing climate. Perspectives for the Twenty-First Century To determine the imperatives for research in the coming decades, one must note the results of the past few decades of research, including both the explicit advances in knowledge and the increased potential to address the remaining critical uncertainties, and must recognize the importance of climatic research for society. Insights of the Twentieth Century A broad interest in climate variability and climate change was awakened in the early 1970s and during the 1980s due to a large number of weather-related disasters in widely scattered parts of the world and to accumulating evidence that human activities are altering the concentrations of radiatively important trace gases in the atmosphere. This awakening resulted in a large dedicated effort, through both the WCRP and national efforts, such as the U.S. National Climate Program and the U.S. Global Change Research Program (USGCRP), to enhance and analyze observations, conduct process studies, and improve climate models. The principal goal has been to develop credible methods to predict climate variability and change. The insights gained from these efforts are diverse and numerous. The three sections that follow illustrate the state of the science. Seasonal-to-Interannual Variability and the El Niño/Southern Oscillation ENSO is a major global-scale signal of seasonal-to-interannual climate variability. ENSO consists of both warm and cold phases, with the warm El Niño phase attracting most public attention. The El Niño phenomenon is an anomalous warming of surface ocean waters in the central to eastern equatorial Pacific Ocean accompanied by large-scale anomalies in rainfall (Figure II.5.1). El Niño occurs irregularly with a typical time period of three to six years. It has been known throughout the twentieth century, mostly through its detrimental effects

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Page 280 FigureII.5.1 Schematic of large-scale climate anomalies associated with the warm phase of the Southern Oscillation during Northern  Hemisphere winter. Based on Ropelewski and Halpert (1986, 1987) and Halpert and Ropelewski (1992). Source: NRC,  1994a.

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Page 281 on the fisheries, agriculture, and water resources of countries bordering the tropical Pacific, but only in the past 20 years has major progress been made in understanding the mechanisms that create ENSO and observing its occurrence and wide-ranging impacts. The 1982-1983 warming, the largest of the twentieth century, was neither predicted in advance nor recognized until nearly at its peak. The enormous worldwide damage directly attributable to this warming (floods in Peru, collapse of the Peruvian anchoveta fishery, devastating drought, and forest fires in Australia and Borneo) gave impetus to an emphasis on observing the tropical Pacific in real time and on predicting the phases and intensity of ENSO. As a result, the international TOGA program of the WCRP was developed. The accomplishments of TOGA, including major contributions by U.S. scientists, are many (NRC, 1996c): 1. The TOGA observing system, consisting of 65 TAO moorings, expendable bathythermographs (XBTs), drifting buoys, tide gauges, upper-air integrated sounding systems, and volunteer observing ships (Figure II.5.2)—all telemetering to the global telecommunication system (GTS) in real time—allows an unprecedented look at the state of the atmosphere, sea surface and subsurface tropical Pacific in real time (McPhaden et al., 1998). Figure II.5.2 The TOGA observing system (TAO). SOURCE: NRC, 1996c.

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Page 282 Figure II.5.3 (A) Observed Sea Surface Temperature Anomalies (SSTA) In Tropical Pacific And (B)  Prediction Made 12 Months In Advance By Cane And Zebiak (1987). Reprinted With  Permission Of The Royal Meteorological Society. 2. A set of theories about ENSO has been developed and the mechanisms that may be responsible for its irregularity have been identified (Battisti and Sarachik, 1995; Neelin et al., 1998). 3. Connections between warming in the equatorial Pacific and climate phenomena in other parts of the world have been demonstrated, and the dynamical mechanisms responsible for these connections are beginning to be understood (Lau and Nath, 1994; Trenberth et al., 1998). 4. Coupled atmosphere-ocean models have been developed that are capable of simulating the major features of ENSO in the tropical Pacific (Zebiak and Cane, 1987; Delecluse et al., 1998). 5. Significant skill beyond persistence has been demonstrated in predicting sea surface temperature anomalies (SSTA) in the eastern to central tropical Pacific as much as a year in advance (Figure II.5.3) (Latif et al., 1994, 1998). 6. Prediction systems, consisting of coupled atmosphere-ocean models, data

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Page 314 search program to study the mechanisms for decadal-to-centennial variability and the implications for longer time-scale predictability. Currently, planning for this element is incorporated in the Dec-Cen and anthropogenic climate change components of the WCRP. Objective 6 Continue to improve the analysis and predictive skill of the degree to which humans are affecting climate, including changes in variability and the probability of extreme events. Analysis of how humans can potentially affect climate and its variability is carried out with a hierarchy of global climate models and observational data sets. Studies with these models indicate that the nature of global and regional climate is in danger of changing due to human activities, most notably in response to increases in greenhouse gases, aerosols, and changes in land use. However, the nature and timing of this change are uncertain. The prediction of future climate change is problematic, in part, because of an inadequate understanding of climate variability, the difficulty of predicting future greenhouse gas and aerosol concentrations, and a limited understanding of the behavior of the coupled climate system. Current climate predictions based on projected increases in greenhouse gases and aerosols indicate the potential for large and rapid climate change relative to the historical record. Improved knowledge of the fully coupled climate system can lead to an enhanced predictive capability that could support societal efforts to adjust to, forestall, or even eliminate some of the negative impacts of projected climate change. This enhanced ability to predict future climate will have a positive impact on economic vitality and national security. The research of the last decade has clearly identified a number of key factors that require a reduction in uncertainty if progress is to be made in climate prediction: First, the current observational system does not measure all of the key global factors that force climate change. For example, despite years of debate about the role of solar variations in explaining observed climate fluctuations, we lack a long-term, consistent, calibrated measure of solar input to the Earth system. Similarly, measures of global aerosol concentrations and character are inadequate to assess its role in climate. Without an enhanced climate observing system, such debates are likely to continue without satisfactory resolution. Second, substantial debate concerning the nature of climate sensitivity to increases in carbon dioxide stems from uncertainties in the measurement of water vapor in the upper troposphere and in the nature of climate-water vapor feedbacks. The nature of this debate demands improved measurement of water vapor.

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Page 315 Third, much of the uncertainty involves ocean-atmosphere coupling, land-vegetation-atmosphere coupling, sea ice modeling, and cloud-climate interactions. Process studies that combine the use of fine-scale regional models, field programs, and diagnostic analysis to bridge the spatial and temporal gaps between observations and typical scales of climate models offer great promise of improving model parameterizations. Diagnostic analysis of paleoclimate and historical data sets can also increase understanding of processes involved in climate change. These studies carded out for a number of large-scale conditions will lead to generalized parameterizations for a range of physical processes (e.g., clouds, sea ice). Reduced uncertainty in modeling surface energy budgets through improved cloud parameterizations will increase the reliability of coupled atmosphere-ocean-land modeling. Furthermore, increased resolution of ocean models will enhance understanding of the coupled system. Systematic analysis of these various climate components should reduce climate drift of the coupled system. Fourth, experience with weather forecasting models suggests that increased spatial resolution results in improved prediction. In addition, the aspects of climate and climate change prediction of greatest relevance to humans and to ecosystems are those that impact water, water resources, weather hazards, agricultural yields, and human health. Most GCM simulations are at spatial scales that are too coarse for credible climate impact analysis. Increased spatial resolution must be matched with better physical representations. Fifth, model-data comparison is critical to diagnose and improve climate model predictions. In many cases, the suite of satellite and in situ data sets has been underutilized in efforts to validate climate models. Further, observations from the industrial period represent too short a time span for satisfactory model validation. Greater confidence in model predictions will be gained through efforts to reproduce industrial, preindustrial, and paleoclimatic data sets. In addition, WCRP efforts to compare climate models based on standard sets of climate simulations through the AMIP (Atmospheric Model Intercomparison Project) process has resulted in increased scrutiny of model parameterizations. The success of this effort has resulted in paleoclimatic intercomparison projects, land surface parameterization comparisons, and intercomparison of limited-area mesoscale models. Continued effort to intercompare models and their parameterization will continue to provide substantial benefit. Finally, increased coordination of climatic research has the potential to yield significant efficiencies. For decades, we have developed observational strategies, promoted and completed process studies and field campaigns, developed a host of atmospheric and oceanic models, and produced impact analyses of climate change based on model output. As yet, however, the path from a proposed new observational strategy or field campaign through to the development of improved model parameterizations or improved application is often not articulated clearly. The cost, in human and financial resources, of major observational

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Page 316 systems and field campaigns is sufficient justification for developing clearly articulated strategies for climate research. The development of more physically based parameterizations for clouds (including their interaction with radiation), coupled atmosphere-ocean models that do not rely on flux corrections to simulate current and historical climates, and multiple examples of coupled Earth system models that adequately represent the major components of the Earth system will be evidence of significant progress in efforts to project future changes in the climate system, including its response to human activities. The efforts to develop a more comprehensive observing system and to construct more comprehensive climate system models should lead to demonstrated progress in reducing uncertainties in the prediction of human-induced climate change. The following requirements are essential to achieve this objective: 1. Develop an enhanced climate observing system capability, with dedicated monitoring programs, as described previously. 2. Focus on key opportunities for reducing major uncertainties in climate models, including improved observations of water vapor and greater understanding of climate-water vapor feedbacks and improved representation of atmospheric chemistry and indirect chemistry-climate interactions. 3. Develop focused process studies with the objective of addressing key uncertainties associated with boundary layer processes and vertical convection; improved linkages coupling the atmosphere, oceans, and land surface; and more explicit representation of land surface processes, including vegetation and soil characteristics. 4. Improve the opportunities to develop coupled models, and enhance efforts at model-observation and model-model comparisons that give particular attention to simulating the observed changes due to changes in solar irradiance, aerosol loadings, and greenhouse gas concentrations. 5. Focus effort on improving the credibility and usefulness of climate model predictions at spatial scales relevant to analysis of the responses of ecosystems, socioeconomic systems, and human health to climate change predictions. 6. Improve the reconstruction, simulation, diagnostic studies, and analysis of data sets from the industrial, preindustrial, and paleoclimatic periods in order to increase confidence in model predictions. 7. Develop clearly articulated linkages between strategies for observation, analysis, model development, and application of predictions to evaluating consequences of climate change. Objective 7 Enhance the linkages between climate model predictions and aspects of the Earth system of immediate relevance to humans (e.g., extreme

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Page 317

Box II.5.1 Necessities for the Twenty-First Century Three clear issues emerge from the discussion of insights gained from research over the past few decades and the scientific and societal drivers of climate and climate change research. These necessities are a follows: 1. Document and understand the mechanisms of natural variability on time scales of seasons to centuries, and assess the predictability of natural variability. 2. Develop prediction, application, and evaluation capability when useful Skill is demonstrated. 3. Project the response of the climate system to human activities. weather events, growing seasons, agricultural yields, and spread of diseases), for the purposes of helping society, realize maximum benefit from whatever skill is demonstrated. Climate variations can have substantial economic impacts, as demonstrated on interannual time scales by the effects of ENSO variation on countries bordering the tropical Pacific. Yet current predictions of climate change generally are not accurate enough or at an appropriate spatial resolution to help provide detailed estimates of future impacts on natural ecosystems, agricultural yields, energy use, emergence and transmission of infectious diseases, and other human activities. Given the magnitude of natural variability on longer time scales and the potentially large impact of human activities on climate, a particularly important objective is to provide reliable regional climate predictions with better characterization of probabilities of extreme events. The nature of the responses of human societies to change depends on human behavior, demographics, vulnerability, and a host of other factors. It is therefore evident that a comprehensive assessment of the impacts of predicted climate changes will require close cooperative studies by social and physical scientists. Such assessment could be used in the formulation of policies that maximize benefits to society. These issues are summarized in Box II.5.1. The following requirements are essential to achieve these necessities: 1. Develop and construct high-resolution, regional climate models along with empirical methods for producing estimates of climate change characteristics of immediate relevance to humans.

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Page 318 2. Develop mechanisms that promote formal interaction between physical scientists and social scientists, by working on common problems to improve the applications and assessments of climate change impacts. Priorities for Climate Research Climate research objectives and their associated requirements can be summarized as four major priorities: 1 Build a permanent climate observing system. 2. Extend the instrumented climate record through the development of integrated historical and proxy data sets. 3. Continue and expand diagnostic efforts and process study research to elucidate key climate variability and change processes. 4. Construct and evaluate models that are increasingly comprehensive, incorporating all major components of the climate system. These four priorities offer a general framework, whereas the objectives and requirements described previously characterize more specific opportunities to promote significant advancement in climate and climate change research. To some, the list of requirements outlined in the previous section may appear overly ambitious and without priority. However, a comprehensive climate research program that serves societal needs is clearly within our grasp. In many cases, programs required to achieve the objectives outlined in this report are in place. In other cases, changes in requirements can be implemented with minimum budgetary impact. In still other cases, objectives can be fulfilled by increased collaboration and closer interagency planning and linkages. However, even some of the more logical, minimal-impact issues appear to be problematic. For example, in terms of the requirement for continuity and quality as part of the climate observing system, current policies verge on becoming a national and international embarrassment. Addressing these issues must be a priority. Finally, with careful planning to achieve greater efficiencies, the full spectrum of climate objectives should be realizable. There are two primary areas in which greater efficiency has the potential to allow an expanded, and more successful research agenda. The first involves convergence of satellite systems in order to credibly and carefully address both research and mission needs. The second area involves greater coordination of major field and process study campaigns in order to serve multiple scientific objectives. Although each of the listed requirements has substantial merit, we recognize that improvements and augmentations of U.S. climate research programs must still be paced, based on budgetary and other considerations. Consequently, the list of requirements described in the previous section is repeated below but within a prioritized framework. This prioritized framework is based on a relatively

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Page 319 simple perspective. Improvements that have minimal budgetary impact but substantial merit should be implemented without hesitation. Requirements with significant programmatic or budgetary implications should have identifiable levels of priority or clear trade-offs with current efforts. Build a Permanent Climate Observing System Requirements with Minimal Budgetary Impact • Where feasible, adopt consistent data collection and management rules to ensure the utility of operational and research system measurements for climate research. • Develop and adopt interagency plans to ensure the protection of critical long-term observations, to limit gaps in continuity due to small budget changes in single agencies and to recognize the value of these observations in a balanced, integrated research program. • Provide strong U.S. support and participation in the development of a global climate observing system. • Ensure full and open international exchange of data and information. Requirements with Significant Budgetary or Programmatic Impact • Maintain major research observation systems, such as the TOGA TAO array, that have demonstrated clear predictive value. • Focus on key opportunities for reducing major uncertainties in climate models, including improved observations of water vapor. • Ensure full interagency commitment to both the in situ and the satellite observations necessary to address the major uncertainties in our understanding of the climate system, including a commitment to long-term Earth observations of critical variables such as the major climatic forcing factors. The TOGA TAO array is already in existence and has demonstrated value for both research and operational forecasts; thus, its maintenance is a top priority for building a permanent observing system. At issue is moving the costs from research budgets to operational budgets. Operational studies, through four-dimensional assimilation studies, should provide some guidance as to the importance of the current characteristics of station density and distribution, enabling an assessment of minimum costs to operational agencies. Current plans for the National Polar-orbiting Operational Environmental Satellite System (NPOESS), with NASA contributions of advanced sounder instruments, offer the potential to satisfy both operational and research needs for improved observations of water vapor. These plans support this requirement under

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Page 320 current budgets that save dollars through NOAA-Department of Defense-NASA collaboration. Critical remaining issues are (1) to ensure sufficient overlap of instruments in space to develop a long-term record and (2) to provide credible measurement of all major climate forcing factors. The addition of commitments for global aerosol measurement and solar energy input to the Earth system should be priorities. Extend the Instrumented Climate Record Through Development of Integrated Historical and Proxy Data Sets Requirements with Minimal Budgetary Impact • Widely sample the alpine glaciers and ice caps before this important repository of information on natural variability is lost. • Continue efforts to collect and analyze data from around the world from tree rings, lake sediments, corals, and ice cores, and actively pursue high-resolution records from ocean sediments. • Focus research efforts on development and validation of proxy indicators. Continue and Expand Diagnostic Efforts and Process Study Research to Elucidate Key Climate Variability and Change Processes Requirements with Minimal Budgetary Impact • Enhance cross-disciplinary communication and collaboration. • Develop clearly articulated linkages between strategies for observation, analysis, model development, and application of predictions to evaluating consequences of climate change. Requirements with Significant Budgetary or Programmatic Impact • Implement focused research initiatives on processes and in regions that are identified as important for understanding variability in the climate system. • Implement and analyze new observations necessary to understand the processes that couple the components of the Earth system, and improve our understanding of climate variability on decade-to-century time scales. • Develop focused process studies with the objective of addressing key uncertainties associated with boundary layer processes and vertical convection; improved linkages coupling the atmosphere, oceans, and land surface; and more explicit representation of land surface processes, including vegetation and soil characteristics. • Support the development and implementation of a comprehensive research program to study and advance seasonal-to-interannual prediction. Such a program is currently the objective of WCRP's GOALS.

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Page 321 • Support the development and implementation of a comprehensive research program to study the mechanisms of decadal-to-century variability and its implications for longer time scale predictability. Currently, the planning for this element is incorporated in the Dec-Cen and anthropogenic climate change components of the WCRP. The climate community has already begun to focus attention on critical regions, through the follow-on to TOGA (GOALS), which expands the focus from the tropical Pacific to the tropics worldwide; the Dec-Cen portion of CLIVAR, which focuses on important regions for longer-term variability such as the North Atlantic; and GEWEX, which focuses on energy and moisture fluxes, particularly at the land-atmosphere interface. Each of these major programs has well-defined justifications and scientific plans and defined major areas of focused study. Completion of the objectives of these three major WCRP programs and focused study of processes at high latitudes are the top priority for continued process study research that can satisfy many aspects of the research requirements listed above. Research funds should be available following the termination of TOGA efforts for continued support of GOALS. Both GEWEX and Dec-Cen are entrained in U.S. budgets and those of other countries. However, at present, these programs lack sufficient resources to complete their objectives in a timely fashion. This type of problem has plagued programs of the WCRP in the past (NRC, 1992). Three solutions are offered. First, we should continue every effort to provide community-based planning and debate that carefully develops priorities and advises on implementation in an efficient manner. Second, every effort should be applied to develop greater coordination of major field and process study campaigns across WCRP and U.S. efforts in order to serve multiple scientific objectives. This may well provide some of the added resources to enable completion of climate research objectives. Third, we must recognize that these efforts are strong candidates for added support. Construct and Evaluate Models That Are Increasingly Comprehensive, Incorporating All Major Components of the Climate System Requirements with Minimal Budgetary Impact • Improve opportunities and enhance efforts at model observation and model-model comparisons that give particular attention to simulating observed changes associated with solar irradiance, aerosol loadings, and greenhouse gas concentrations. • Develop mechanisms that promote formal interaction between physical scientists and social scientists, by working on common problems to improve the applications and assessments of climate change impacts.

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Page 322 Requirements with Significant Budgetary or Programmatic Impact • Enhance the computational infrastructure and the focused efforts to develop climate system models that include explicit representation of atmosphere, ocean, biosphere, and cryosphere. • Focus on key opportunities for reducing major uncertainties in climate models, including greater understanding of climate-water vapor feedbacks and improved representation of atmospheric chemistry and indirect chemistry-climate interactions. • Focus effort on improving the credibility and usefulness of climate model predictions at spatial scales relevant to analysis of the responses of ecosystems, socioeconomic systems, and human health to climate change predictions. • Develop and construct high-resolution, regional climate models along with empirical methods for producing estimates of climate change characteristics of immediate relevance to humans. The observation and process study research described above are key to reducing major uncertainties in climate models and improving the representation of the atmosphere, ocean, biosphere, and cryosphere interfaces. If these efforts move forward, the major requirement will be (1) to have dedicated computational and human resources for the development of coupled system models, and (2) to develop clearly articulated linkages between strategies for observation, analysis, model development, and application of predictions to evaluating consequences of climate change. Increased computational capability with its associated human resources is critical and costly, but is a priority for additional climate research funding. The second priority, which is complementary to improved coupled system models, is the development of higher-resolution models suitable for producing estimates of climate change of relevance to humans. Increased computational capability, associated with high levels of research effort, is the first step toward fulfilling this requirement. Cross-Cutting Requirements Education Education must be an important facet of the perspective and activities in climate and climate change research entering the twenty-first century. Three elements are of particular importance. First, the general level of public understanding on issues of climate and climate change is disheartening and clearly limits perceptions of the importance of climate research and the development and acceptance of national and international policy. Outreach, contributions to the popular press, and speaking to the general public must be encouraged and rewarded as mechanisms to increase public knowledge of climate and climate

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Page 323 change. Second, the long-term health of research programs and their applications depends on a strong background in math and science, beginning with K-12 education, and a strong interest in atmospheric, oceanic, and related sciences. We must inject the importance and excitement of our disciplines into both K-12 and undergraduate educational programs in order to develop and attract the most capable climate researchers. The climate research community should take an active role in enhancing K-12 education through providing up-to-date materials and participating in teacher training. Third, we must maintain and strengthen graduate programs oriented toward the critical scientific questions that define limitations in our understanding of climate. Graduate training in climate at universities is best enhanced by (1) added interdisciplinary efforts directed toward climate as a discipline, and (2) educational efforts directed toward increasing the skills required to develop large-scale models of the Earth system and the skills needed to develop and maintain observational systems. Current training is often inadequate because much of the focused effort occurs at national laboratories and other nonuniversity facilities. Institutional Arrangements Diverse institutional arrangements are required to address climate research needs. Community perceptions are that our institutional arrangements are actually becoming less diverse. Over the past two decades the nature of our institutional arrangements both to fund and to conduct research has become homogenized. Research support has tended increasingly to favor projects with short-term payoffs regardless of whether the research is performed at universities or national laboratories. Both funding mechanisms and institutional evaluation of research (including promotion and salaries) have tended to limit long-term comprehensive projects that lack short-term results. For example, national laboratories have adapted a university faculty-type staff evaluation method based on publications and grants, despite very different missions. The trend of homogenization of our institutions must be reversed in order to promote better opportunities to develop long-term sustained efforts. Such efforts are required to develop and manage data sets and observational systems, and to develop comprehensive models of the climate system. Both funding efforts and the evaluation of research efforts must serve to promote critical projects that do not have annual payoffs, when warranted by the nature of the problem. Funding agencies tend to provide opportunities for individual projects and large-scale research efforts (i.e., centers or named programs). Intermediate-sized teams also are important in interdisciplinary efforts or for the issues needed to solve many climate problems. Funding agencies must be able to provide opportunities for a broad range of projects involving single and multiple investigators. Third, some elements of climate research, in particular the development of increased predictive skill, are more efficiently accomplished with dedicated facilities. Dedicated centers—for example, in cli-

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Page 324 mate prediction—must be established when warranted by the potential for increased efficiencies or by their potential to catalyze research efforts. Diversity in our institutions is important to promote efficient, sustained efforts that address the major scientific issues in climate research. Contributions to National Goals and Needs A robust climate research program is likely to contribute substantially to national goals and needs. Nine major contributions can be identified: 1. operational predictions of interannual climate fluctuations up to one year in the future; 2. detection of natural climate variations on decadal time scales and increased understanding of their causes and impacts; 3. plausible climate change scenarios for regional climate and ecosystem change, suitable for impact analysis; 4. improved estimates of the relative global warming potential of various gases and aerosols, including their interactions and indirect effects of other chemical species; 5. improved ability to determine the regional sources and sinks for atmospheric carbon dioxide; 6. reduction in the range of predictions of the rate and magnitude of global warming over the next century; 7. predictions of anthropogenic interdecadal changes in regional climate, in the context of natural variability; 8. documentation of the level of greenhouse gas-induced global warming and documentation of other climatically significant changes in the global environment; and 9. improved understanding of the interactions of human societies with the global environment, enabling quantitative analyses of existing and anticipated patterns of change.