Domains of Human Vulnerability and Global-Scale Processes
Domains of human vulnerability—food, water, energy, shelter, and health—are areas of critical importance to society and each is vulnerable to the impacts of climate change. As climate change impacts have the potential to affect the interaction of human vulnerabilities and exposure(s) to some environmental change, it is valuable to examine the link between a climate-relevant global process and the critical systems upon which humans depend, specifically the domains of human vulnerability, in order to better understand indicators of environmental sustainability.
Identifying the Earth observing systems that would be appropriate for monitoring environmental change and, ultimately, environmental sustainability could be an endless task. However, it is feasible to sort through the myriad of possibilities to distinguish areas of particular importance within the domains of human vulnerability where change is likely to be dramatic and occur in the near-term, and where impacts on humans start to be significant. Incorporate one more factor—measurability (i.e., that the indicator is significant enough to measure and methods exist to do so)—and we begin to develop an approach to identifying indicators of environmental sustainability.
The following sections examine domains of human vulnerability to illustrate the types of linkages that the committee considers to be possible. These domains constitute one defining feature of global environmental change, are not place-bound, but are replications of stress in many locations across the globe.
Agriculture has complex vulnerabilities to climate change and is very sensitive to hydrological and economic conditions. As agriculture becomes industrialized, crops are produced in less than ideal environments. Wheat, for example, would grow best in regions that are dedicated to the more profitable crop, maize. Crops also are often produced in proximity to the infrastructure for their processing and transporting. In this sense, crops sometimes are decoupled from the most fertile climate conditions.
There are at least five broad agricultural systems that might be monitored to produce insights into environmental sustainability. Four categories can be formed from
the combinations of rain-fed versus irrigated agriculture with C3-photosynthetic10 versus C4-photosynthetic plants11. A fifth category involves animal pasturing. These five pathways provide the majority of food consumed by humans.
Rain-fed agriculture is clearly a system at risk in places where climate change brings decreased rainfall and/or increased temperatures during the growing season (and an associated increased demand for water by the plants). Irrigated agriculture may be relatively less vulnerable to the direct consequences of climate change, but the increased use of irrigated water competes with other demands for water. C3 plants are potentially aided by increased atmospheric carbon dioxide (CO2) in terms of an increased photosynthesis rate and increased water-use efficiency; C4 plants do not feature this response (Derner et al., 2003). Grazing systems are vulnerable to water supply for plant productivity and for animal consumption. With climate change, grazing systems can feature catastrophic collapse and can result in longer-term systems degradation.
Agricultural systems are monitored by a variety of technologies including overhead surveillance, which are used in designing production strategies, monitoring irrigation schemes, and assessing the state of crops (DeFries, 2008; NRC, 2008b). Remote-sensing technologies also are significantly applied in commodities prediction (Supit, 1997; Haboudane et al., 2002). Many models are successful at predicting agricultural production for a variety of crops (McCown et al., 1996; Stoorvogel et al., 2004). However, their application to altered climatic conditions is an existing challenge.
Unlike fisheries systems discussed in the next section, mass agricultural production systems are primarily engineered by humans and feature organisms (both plants and animals) that are highly modified genetically through domestication. This coupling of modern agriculture’s technological dependency with the nature of the agricultural species makes the response of agricultural systems to climate change extremely complex to interpret. Additionally the market-driven economic drivers of global commodities markets and agricultural policy restrictions on crop overproduction also complicate the interpretation of vulnerabilities. Food is an essential commodity in world trade, and wealthy nations can buy food when poorer nations cannot.
In early assessments of the potential consequences on agriculture of climate change, it generally was thought that the crop production systems would adjust by using new breeds of crop varieties and/or use crops or varieties of crops from other regions to maintain local and regional agricultural productivity. The remarkable climatic domain within which one can grow a crop such as maize formed some of the basis for these opinions. So did the success of the “Green Revolution” in increasing crop yields in previously marginal situations. However, the metrics in the Land-Surface and Terrestrial Ecosystems Table (Chapter 3) emphasize the monitoring of rain-fed, subsistence agricultural systems, which have less of a technological buffer from climate variation than do advanced technology agricultural systems. Similarly, dry-land grazing systems are also considered. These production systems have the potential to serve as early-
warning systems for climate’s effects on crops. They also are the modes of food production for some of the regions that are most vulnerable to climate-related food shortages.
Fisheries are another example of a domain of human vulnerability (food), highlighting the intersection of human needs and climate change. As documented in numerous reports (e.g., MEA, 2005), the world’s fisheries are under enormous stress, with some of them severely overfished (Figure 2-1), even without the added stress of climate change. Pressures have spread to more distant locations as well as to new species (FAO, 2005). How do we sustain resilient marine ecosystems in the face of these pressures?
Aquaculture (both in confined facilities and in more traditional hatcheries) has altered the composition of the food supply, as well as of wild fish populations (Naylor et al., 2000). Moreover, aquaculture in many regions has resulted in significant changes in land and ocean use (e.g., conversion of mangrove forests into shrimp farms in Southeast Asia, blocking off fjords in Norway and Chile for salmon and halibut farms). Both confined and at-sea aquaculture systems can alter the genetic diversity of wild populations as well as introduce diseases into the environment. Additionally, human activity indirectly impacts marine ecosystems. Conversion of wetlands and estuaries to agriculture and urban areas, river channels, and dams and levees reduces the availability of critical nursery grounds, and hydroelectric facilities can impede the migration of anadromous fish. Furthermore, riverborne pollution can create hypoxic ocean environments; harmful algal blooms have been increasing in abundance in U.S. coastal waters, thus reducing the availability of a wide range of seafood.
Adding to these already-existing stresses, climate change will alter the underlying physical environment, with significant impacts on all levels of oceanic ecosystems. Shifts in ocean temperatures and currents are enabling warmer water species to move into subarctic waters (Perry et al., 2005). Most nutrients are limiting in the euphotic (“lighted”) zone; the largest nutrient reserves are found at depth (not from land or atmospheric inputs). A warmer ocean is more stratified, thus reducing vertical mixing, which is the main pathway for these deep, nutrient-rich waters to support primary productivity in the upper ocean. This effect, while reducing nutrient input to the upper ocean, may lower global primary productivity (Behrenfeld et al., 2009).
Sea level rise may further reduce the extent of wetlands and estuaries. Ocean acidification, caused by increased CO2, will have implications for marine calcifers, which provide habitat for marine fish and organisms and form the base of the marine food chain. Thus, the interactions between large-scale and regional-scale climate processes and between the natural and the human environments lead to a complex set of interacting issues.
Given that fish, both wild and farmed, provide a substantial amount of protein to the world’s population, including some countries for which they are the dominant source (FAO, 2009), fishery health is an important metric to monitor. Fishery health can be assessed by measuring fishing intensity, ocean productivity, coastal land use, and extent of aquaculture. Spatial and temporal changes in this metric will provide an indication of long-term ecosystem health and environmental sustainability.
Water of sufficient quality and quantity for consumption, washing, agriculture, energy, transportation, and other uses is a critical need for all societies, yet the need is not met for more than 1 billion of Earth’s people (WHO/UNICEF, 2005). The stresses to societies resulting from the lack of water, water of poor quality, or too much water at the wrong time may lead to unsustainable situations. The three feedbacks associated with human society that are most critical to future water distribution, quantity, and quality are climate change, population growth, and modification of land use and land cover.
The global population was estimated at 6.85 billion in 2010 and is expected to grow to 9 billion by mid-century (U.S. Census Bureau, 2010). Water will be affected by population growth through diversion, increased demand, and increased contamination with human waste and industrial byproducts (Dozier et al., 2009). .
To illustrate the ways that water availability might be affected by climate change and add to environmental stress, one can examine and contrast two different environmental settings, alpine and coastal. The committee chose this approach over a comprehensive review of the relationship between water and climate in order to provide depth over breadth. In alpine environments, much of the water is delivered to high elevations as snow. The winter snowpack gradually melts, releasing water to local ecosystems, initiating springtime vegetative growth and faunal behavior, and filling lakes and reservoirs. Later in the season, when the snow has melted, glaciers, if present, gradually release additional water (Figure 2-2).
When the distance between source and use is large, methods of transport (e.g., soil seepage, underground aquifers, and surface streams and rivers) also come into play. Ecosystems come to depend on the particular pattern and timing of water’s availability. Populations without effective reservoirs (either natural or artificial) are more vulnerable to changes in precipitation patterns (amount, timing, and type) and declining glaciers (Bales et al., 2006). Shorter winters and an increase of rain versus snow, cause relatively wetter winters and drier summers, because of runoff during the winter months and a more homogeneous distribution of precipitation owing to a lack of redistribution by wind. Increased atmospheric temperatures or dust or soot in the snow can lead to a similar result, with runoff starting a few weeks earlier and before downstream evaporative demand requires additional water. Glacier loss removes a critical summer water source (Figure 2-3). Changes in soil wetness and in the type of groundcover, driven by altered land uses, also affect the movement of water. Faster transport diminishes the ability to retain water, thereby increasing the need for artificial reservoirs, lest the opportunity to use the water is lost. Faster transport can be self-reinforcing as erosion removes soil and decreases water retention capability (Trimble and Crosson, 2000).
Possible metrics that can be used to indicate the environmental sustainability of the polar environment include the condition and extent of permafrost and the temporal variability of sea ice extent and volume. In the alpine environment, the seasonal progression of the winter’s snowpack and the timing of river and lake ice breakup are already proving to be important cryospheric metrics with direct impact on humans, as is the mass balance of glaciers, ice caps, and ice sheets, through its direct connection to sea
level. More than 1 billion people depend on snowmelt for their water resources (Barnett et al., 2005), and the heterogeneous redistribution of snow by wind leaves areas of deeper snow that persist well into the summer and provide late-season soil moisture.
The coastal urban environment is considerably different from the alpine environment and is particularly important because nearly half the world’s population lives at or near the coast. At these lower elevations, precipitation generally is received as rain rather than snow. Although the ocean affords a seemingly endless reservoir of water, desalination of ocean water has proven to be difficult and expensive (Cooley et al., 2006). Rising sea level (Figure 2-4), which can occur as a result of melting ice sheets or glaciers, warming ocean temperatures, and vertical lithospheric motions, can threaten coastal facilities, especially if combined with severe weather events (e.g., hurricanes) and storm surges during elevated tidal conditions (Figure 2-5).
Possible metrics that can be used to indicate the environmental sustainability of coastal environments include river flow, ice sheet and glacier mass changes, local precipitation trends, hurricane frequency and location, and sea level rise.
Monitoring water-related metrics—such as total terrestrial water storage, seasonal snow, and water quality—and improving scientific understanding will enable more reliable predictions of the response of Earth and human systems to varying climate and changing human interventions in the water cycle. Monitoring these metrics, may be one tool that can help decision makers employ predictive, adaptive management.
Dozier et al. determined that monitoring water poses the following three major challenges (2009):
“In general, the water cycle, with its intrinsic variability and the changes that human activities cause at all scales, is a unifying concept. However, closing the water balance and predicting flows between stores in our coupled natural and engineered water systems remain difficult.
The human need for reliable and safe water supplies and protection from floods has created complex engineering systems, along with
societal decision making processes, that are essential but sometimes fail.
The variability of the water cycle and the interaction of humans with the natural and engineered environments have led to social structures and organizations that add complexity and uncertainty.”
The quantity and quality of our water environment is altered by human development either through intentional intervention or as a result of urbanization, agriculture, energy generation, and economic development (Dozier et al., 2009). For example, growing urban areas are associated with high-volume runoff events, which induce poorer water quality downstream. Alterations to the water cycle are increasing and are frequently observed on larger scales. Growing nutrient loadings in a given drainage basin typically results in coastal hypoxia (Figure 2-6; Dozier et al., 2009). Evidence suggests that an increase in ambient CO2 inhibits plants’ assimilation of nitrate from the soil, meaning they cannot process a larger CO2 load when nitrate from soil is their primary source of nitrogen. Researchers note that plants may yet adapt to increased CO2 levels, but once this occurs, plants will need to draw more and more nitrate from the soil (Bloom et al., 2010; Finzi et al., 2006). Humans may be able to restore soil balance with ammonium- and nitrate-based fertilizers, but that would increase reliance on fertilizers, which ultimately will lead to more hypoxia and algal blooms.
The interactions between and couplings of climate, population, urbanization, and development, as well as how they affect water, have been largely outside the scope of most analyses. Population growth and the consequent increase in water demand must cause the strategies for water management to change. Historically, we have tried to manage supply to meet demand, but in the future we must also manage demand itself. Climate change requires reorientation of analyses involving water from their traditional focus on forecasting and risk analysis to embracing decision making under uncertainty. Rarely will all uncertainties about climate change and relevant stressors be resolved before decisions should be made about water infrastructure or response to floods or droughts. Anticipating and predicting water issues means that future scenarios that fall outside of historical experience must be considered, along with the consequences of specific decisions in a complex coupled human-environment system. Identifying and monitoring metrics that can be used to indicate the environmental sustainability of water will require not only the biophysical elements of the water cycle but also relevant information about human interactions and feedbacks.
Another critical domain of human vulnerability is energy. Energy systems have a significant impact on human-environment interactions. From fossil fuel-based power plants, to hydroelectric systems, to automobiles and airplanes, production and utilization of energy not only sustain human systems but also drive anthropogenic input of CO2 to the atmosphere. Over the next few decades, there will be significant political and economic pressures to “decarbonize” as well as to increase the efficiency of energy systems. These pressures will inevitably result in new sources of energy, all of which may have potentially unforeseen, environmental impact.
There has been considerable research on the role of the energy sector in emissions of CO2 and on the development of technologies that could result in increased energy efficiency (NRC, 2009b). However, there has been considerably less research on the implications of deployment of these technologies on the coupled human-environment system. Biofuels will place pressure on food availability as well as increase demands on water supplies as crops are switched from food to fuel production (NRC, 2008c). Offshore energy systems (ranging from deep ocean drilling platforms to wave and tidal energy systems) will affect ocean circulation and marine ecosystems (Figure 2-7). Low-capacity but highly distributed nuclear reactors (in the few megawatt range) as well as increased numbers of larger plants could increase the risks of nuclear proliferation while carbon emissions are decreased (NRC 2009b).
All of these interactions will be further stressed by the patterns of climate change. For example, changes in natural disasters such as hurricanes, floods, and droughts will potentially disrupt a wide range of energy system operations, including transmission lines, oil and gas platforms, ports, refineries, wind farms, and solar installations. As air
temperatures rise in many regions, there will be an increase in energy demands for cooling and a decrease in energy demands for heating. Water limitations in parts of the world, and an increased demand for water for other uses, could result in less water for use in cooling at thermal electric plants as well effects on hydropower sites (NRC, 2010a).
Given that climate change will affect our energy systems and that energy systems play a significant role in the coupled human-earth system, it may be important in the future to develop metrics that will provide an indication of environmental sustainability.
“SHELTER” AND NATURAL DISASTERS
“Shelter” is added to the list of critical systems on which human beings depend because although we have adapted ourselves and our activities to average conditions on Earth (e.g., temperature, precipitation, wind), we have been less successful in accommodating extremes. Extremes such as heat and cold, flood and drought, and wildfire are not incidental to Earth system processes. Rather, they are fundamental. As a result, natural disasters are sensitive (albeit noisy) indicators of environmental sustainability. Disaster costs vary globally and significantly from year-to-year, but they are trending upward more rapidly than are inflation and growth in world gross domestic product (Munich Re, 2010), a trend that reflects several factors. The first is the increased exposure to hazards, that is, an increase in population combined with increasing property values and patterns of urbanization, especially in high-risk areas such as coasts, floodplains, and seismically active zones. The globalization of economic activity and its
increasing reliance on critical infrastructure also play a role. Frequently, disruption of the economy competes with damage to structures as the main economic loss from a natural disaster. Finally, there is the influence of climate change itself on natural disasters, such as floods, droughts, wildfires, and severe storms. While not all natural disasters are related to climate change, some, such as wildfires, may be and thereby serve as another intersection of climate change and human systems (Figure 2-8).
Wildfire provides a clear illustration of the potential relationship between the impact of climate change and human vulnerability to a climate-related natural disaster. Humans and climate both play roles in determining fire patterns. In turn, fire influences the climate through release to the atmosphere of carbon stored in the biomass (Bowman et al., 2009). Weather/climate, fuels, ignition agents, and human activities all have a strong influence on fire activity. (Flannigan, 2009). Climate drives large, regional fire through antecedent wet periods that create substantial herbaceous fuels or drought and warming that extend conducive fire weather (Bowman et al., 2009). Although wildfires are influenced by a range of climate parameters (e.g., temperature, humidity, precipitation, wind speed, lightning occurrence), in the long term, temperature may be one of the best predictors of future area burned. For example, in Canada, it appears that warmer temperatures are associated with increased area burned (Flannigan et al., 2005).
The role of human activities is another important factor. People enhance a region’s vulnerability to wildfires by fragmenting or abutting forests with development.
In North America, population growth and expanding development into traditionally non-urban areas have increasingly brought humans into contact with wildfires. In the western United States alone, 38 percent of new home construction is adjacent to or intermixed with the wildland-urban interface. People also cause fires. The U.S. National Association of State Foresters (2010) estimates that 90 percent of all U.S. wildfires are caused by people. In Canada, human-caused fires make up a little more than 50 percent of all fires (Flannigan, 2010).
Fire frequency in a given area is largely dependent on the existing “fire regime,” which is driven by ecological, meteorological, and human factors. A change in fire regime characteristics (and, thus, a given region’s vulnerability to fire) due to a changing climate and human decisions (e.g., land use) may be an important driver of future ecosystem processes in many forested regions (Kasischke and Turetsky, 2006). Improved monitoring of fires and deforestation using satellite imagery could allow for a better quantification of wildfire activity. For more information on metrics related to natural disasters, see Tables 3-6 and 3-7.
Human health is the fifth domain of human vulnerability. Understanding societal impacts of climate change at the global level requires, first and foremost, the understanding that many factors interact with a given impact. Each factor derives from a complex mix of causes and effects. Effects of climate change on food supplies will potentially result in disputes and civil strife over competition for declining resources, especially with respect to fishery stocks and fish species. Similarly, agriculture at the international level will undergo shifting patterns of harvests and altered plantings of staple food crops. Changes in food supplies, and ultimately shortages, can be predicted, as well as reappearance of famine in the less-developed countries (Parry et al., 2005; Davis and Belkin, 2008).
Change in sea level is predicted to result in potentially catastrophic effects on island nations and low-lying coastal regions, with the most severe occurring in densely populated countries like Bangladesh, where a portion of the country would become uninhabitable (Dasgupta et al., 2007). The resulting millions of refugees would pose enormous social, civil, economic, and security challenges for those nations most likely to receive them, namely the United States, and countries within Europe and Latin America. Africa and the Middle East, already embroiled in conflicts, will be impacted not only by population ebb and flow due to sea level rise, but also refugee populations escaping the areas of military action, further destabilizing a relatively fragile political environment (NIC, 2009).
This population ebb and flow in developing countries as a result of sea level rise may increase the risk of diseases spreading (Spokes, 2004). Furthermore, sea level rise combined with higher temperatures in many coastal regions will create new reservoirs of warm, brackish, stagnant water, ideal for breeding mosquitoes that can transmit malaria, dengue fever, and many other tropical mosquito-borne diseases (Craig, 2010). The warming sea itself is a reservoir of disease bacteria and viruses, and rising sea levels
could expose new and more extensive populations to diseases such as cholera (Craig, 2010).
Water source and safety represent the most critical indicators with direct measureable impacts on health. Waterborne diseases are directly correlated with quality and quantity of clean water. Similarly air quality, food production, and other factors related to environmental sustainability of human systems are impacted by human health and other dimensions. Globally, diarrheal diseases currently represent the second most likely cause of death of children under the age of five in the less-developed countries (Bryce et al., 2005), meriting significant attention with respect to climate. Many cases are the result of poor drinking water quality. For example, receding glaciers and disappearance of snow in mountainous regions will threaten the availability of freshwater sources for populated regions. These changes, in addition to those caused by inadequate government services in terms of water supply management and health infrastructure, if extensive, can be predicted to foment civil disruption and social/economic irregularities, not the least of which may be more extensive epidemics and concomitant social stress (Campbell et al., 2007; CNA, 2007). If a government is dealing with a serious cholera epidemic caused by the interruption of drinking water treatment and if its water supply is significantly reduced in quantity and quality, then the civil and social disturbances caused by the epidemic will be exacerbated. In addition, on a global scale, interruption of commerce, trade, and travel will be impacted. Millions of dollars were lost during the cholera epidemics in Latin America in 1991-1992 (Susrez and Bradford, 1993).
Any health outcome that is influenced by environmental conditions may be impacted by a changing climate. However, the linkages between climate change and shifting patterns of health threats and outcomes are complicated by factors such as wealth, distribution of income, status of public health infrastructure, provision of preventive and acute medical care, and access to and appropriate use of health care information. Furthermore, the severity of future health impacts will be influenced by strategies to limit and adapt to climate change (NRC 2010a). These factors make it difficult to identify climate change metrics for human health since human health, welfare, and social well-being will be affected in multiple ways, with the end results directly derived from complex interactions of the factors for which metrics are presented in Chapter 3.
EARTH SYSTEM LINKAGES TO GLOBAL CLIMATE CHANGE AND ENVIRONMENTAL SUSTAINABILITY
A broad array of indicators, based on a great diversity of measurements, could provide advance warning of the impacts of global climate change. But because it is both uneconomical and fundamentally impossible to measure everything, it is important to develop priorities—to identify some select, finite suite of indicators that, taken together, provide a generally accurate and informative basis for anticipating problems. This is not to say that all measures are not to some degree important, but rather that some measures are likely to be especially telling.
The committee finds that observations of global-scale processes are especially valuable from an indicators perspective. A global-scale process is one that is manifested
in all regions of the planet, such as the biogeochemical cycles of carbon and nitrogen, the hydrologic cycle, or ocean acidification (Box 2-1). They reflect both the impacts of climate change, as well as the feedbacks and forcings that might change the direction, scale, or timeframe of the impacts.
The oceans are natural sinks for carbon dioxide (CO2), but as our understanding of this process has increased we can again see the complexity of the systems and feedbacks at work. To date, it is estimated that the oceans have absorbed about one-third of man-made CO2, helping to regulate the amount of CO2 in the atmosphere. However, recent observations have shown that changes in ocean chemistry, driven by increased atmospheric CO2 during the past century, are lowering the pH of seawater and reducing the carbonate ion concentration (Figure 2-9). This results in ocean acidification, a phenomenon that has diverse implications for the marine environment (Feely et al., 2004, 2008; Iglesias-Rodriguez et al., 2008). The increase in ocean acidity is corrosive to marine shells and organisms, such as corals, foraminifera, coccolithophores, and pteropods, that provide habitat for marine fish and organisms and form the base of the marine food chain.
The full ecological impacts of ocean acidification are only beginning to be discerned. For example, coastal waters in the Pacific Northwest were found to be undersaturated in aragonite, which could have serious impacts for marine calcifiers for shell and skeleton formation (Feely et al., 2008). Decreased availability of aragonite and other calcium carbonates will lead to increases in both the energetic costs of shell building and the rate at which shells dissolve.
Understanding of ocean acidification and its impacts on marine ecosystems and biogeochemistry will require both long-term, comprehensive studies of physical/biological systems and detailed process studies in specific target areas (Doney et al., 2009). A global observing system (both spaced-based and in situ) will be required to monitor the large-scale patterns and dynamics of ocean circulation, heat content, primary productivity, carbon absorption, and other variables. Process studies will be needed to ascertain the ecosystem response to ocean acidification, which will vary considerably from system to system. These responses will include changes in ecosystem health composition. Coral reef ecosystems are likely candidates to show the detrimental effects of acidification, although coral reefs are stressed by other factors as well (e.g.., pollution, overfishing, climate change, and coral mining). Systems that support important ocean fisheries are also significant, such as the upwelling ecosystem off the Pacific Northwest, Georges Bank, coastal Chile, and the Bering Sea.
An emphasis on global-scale processes provides insights into linkages within the Earth system that extend from the atmosphere to the oceans, from the cryosphere to the hydrosphere, and include the land-surface, human health, and natural disasters (Box 2-2). Observations of selected indicators, taken in some careful combination, provide a fingerprint of change across multiple variables in multiple systems and can be used to search for high-level patterns. Factors to be considered when selecting global-scale processes for observation include:
Is the global-scale process of societal relevance and likely to remain important over the next century?
Is change in this process likely?
Is the change measurable, especially given that small changes are difficult to measure in the presence of large variations related to, for example, seasonal or annual variability?
Can the measurement be sustained given the realities of budgets and instruments?
Examples of Earth System Linkages to Global Climate Change and Environmental Sustainability
The committee has divided metrics into seven topical areas (oceanography, land-surface, atmosphere, cryosphere, hydrology, human health and dimensions, and natural disasters; see Chapter 3). However this division of the physical world can overlook important cross-links between areas. Some of these cross-links are extremely important but may not have received as much attention as discipline-focused areas of study because
much of scientific inquiry is grounded in a single discipline. Some examples of important cross-links are as follows:
Global warming leads to shifts in the atmospheric jet stream which increases the intensity of upwelling events off the Pacific Northwest coast resulting in more resuspension of iron-rich bottom sediments leading to increased primary productivity in the coastal ocean which in turn lowers oxygen levels in bottomwaters as blooms decay resulting in hypoxic zones.
Ocean circulation and changes in the atmospheric circulation drive the change in the type (temperature) of the water that reaches ice shelves resulting in land ice loss leading to sea level rise and eventually coastal inundation/erosion.
Atmospheric wind and temperature fields affect sea ice cover and the occurrence/extent of sea ice which in turn directly changes the radiation budget which feeds directly back to the atmospheric state.
Precipitation patterns determine the amount of snowpack which drives surface hydrology affecting the relative success of vegetation and agriculture, and people’s dependence thereupon.
Increased CO2 emissions some of which are absorbed by the oceans result in increased ocean acidity which is corrosive to marine shells and organisms that provide critical habitat and/or food sources for other organisms which will negatively impact fisheries worldwide.