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Vulnerability and Adaptation

The Earth's climate has warmed about 0.5°C (0.8°F) over the last century, and is expected to warm another 1.0-3.5°C (1.8-6.3°F) over the next century under "business as usual" scenarios. Though present actions under the Framework Convention on Climate Change (FCCC) will have some effect on future greenhouse gas emissions and the magnitude and rate of additional climate change, significant climate change will occur and will have important consequences for society (IPCC/WMO/UNEP 1996b).

• Human health will be compromised by increases in the rate of heat-related mortality and in the potential for the spread of both vector-borne diseases (such as malaria, dengue, yellow fever, and encephalitis) and nonvector-borne diseases (such as cholera and salmonellosis).
• Food security will be threatened, especially in the tropics and subtropics, where many of the world's poorest people live.
• Water resources will be increasingly stressed, leading to substantial economic, social, and environmental costs, especially in regions that are already water-limited and where there is strong competition among users.
• Human habitat will be lost where small islands and coastal plain and river areas are particularly vulnerable to sea level rise.
• Natural ecosystems will be degraded as their composition, geographic distribution, and productivity shift along with the responses of individual species to changes in climate. This may lead to reductions in biological diversity and in the goods and services society derives from ecosystems

The overall impact of climate change on any single region or sector will depend on the rate and magnitude of change and the vulnerability or sensitivity of the region's natural and human systems to such change. Given these complexities, society and nature may have to simultaneously adapt to rising sea levels, more variable precipitation patterns and temperature extremes, changes in water supplies, disruption of ecosystems, and changes in many other climate-sensitive natural resources. This chapter briefly describes the U.S. efforts to evaluate vulnerability to climate change and to identify key measures that may reduce its risks.

Enhancing the Adaptability of Natural Systems

Various U.S. planning, regulatory, and policymaking organizations that deal with existing environmental issues have many years of experience and technical expertise in managing natural resources. As the United States explores options to enhance its adaptability to climate change, it must seek solutions that both manage existing pressures and enhance its flexibility to respond to future climate change issues. Such solutions include enhanced contingency planning, ecosystem management, and scientific research and development.

Contingency Planning

Most human institutions and infrastructure assume that the past is a reasonable surrogate for the future. For example, engineers designing reservoirs and other coastal structures use the statistical term "stationarity" to reflect their belief that historical rainfall patterns and coastal processes are reliable indicators of future patterns. And farmers know that inclement weather may destroy their crops, but based on historical averages, expect their crops will succeed in most years.

Climate change poses problems for these approaches to resource management. For example, rainfall is increasing worldwide, and extreme rainfall events (more than 5 centimeters, or 2 inches, a day) have increased about 10 percent over the last century in the United States. Delaying anticipatory measures may leave the United States unprepared for the changes that do occur and may increase the possibility of impacts that are irreversible or that substantially increase the cost of adaptation.

Human adaptation to climate change is distinct from biological adaptation. It can include any means of adjustment to altered conditions, such as biological, technical, institutional, regulatory, behavioral, or economic adjustments. Adaptation can be grouped into three broad categories:

• passive adjustments--e.g., gradual changes in human behavior and tastes, or biologically driven changes in communities);
• deliberate reactive responses --e.g., management responses; and
• anticipatory actions--e.g., planning, engineering, or regulatory responses taken in advance of observed climate change.

Contingency planning minimizes the social, environmental, and economic costs of natural disasters or accidents by addressing immediate natural resource management needs and by increasing the resiliency of those resources to floods, forest fires, droughts, and hurricanes. New anticipatory approaches include developing mitigation strategies based on rigorous identification and assessment of an area's or an ecosystem's vulnerability to climate change and drawing on a wide range of expertise.

For example, following the Great Midwest Flood of 1993, the Scientific Assessment and Strategy Team was assembled from more than a dozen federal agencies. This multidisciplinary team of experts recommended a new approach--managing the Mississippi River Basin floodplain as a system rather than as a patchwork of individual components. The team also recommended returning some agricultural areas to wetlands and improving floodplain management by using more advanced maps and other scientific and technical information.

Similarly, in February 1997 the U.S. Department of Agriculture, the Federal Emergency Management Agency, the Department of the Interior, the Small Business Administration, and the Western Governors Association agreed to a series of measures to systematically address the threat of drought. They formed a Western Coordinating Council and a federal interagency coordinating group to work on drought mitigation, response, and policy, including improved planning, communication, and data management efforts.

Ecosystem Management

An ecosystem is defined as "the combination of organisms living in a region and the physical and chemical environment that they inhabit." Ecosystems themselves do not "adapt" and respond to climate change as a unit; rather, the coexisting ecosystem species may do so.

Some organisms are more tolerant than others to extremes of climate and environmental variability. How well species respond to climate extremes in rainfall and temperature may be a measure of how well they may adapt and be able to withstand future changes without undergoing local or total extinction. Ecosystems are thus subject to disruption by changing climate, as their individual species migrate in response to changing habitats and environments.

Ecosystem Management Task Force

The goal of ecosystem management is to maintain and restore the health of ecological resources affected by pollution, urbanization, changing climate, and other stresses. One of the most far-reaching environmental recommendations of the Clinton Administration's National Performance Review of the federal government was to develop a "proactive approach to ensuring a sustainable economy and a sustainable environment through ecosystem management." This recommendation catalyzed movement toward more holistic approaches to environmental protection and resource conservation efforts.

An interagency Ecosystem Management Task Force was established in 1993, consisting of Assistant Secretaries from twelve federal departments and agencies, as well as representatives from several White House offices, to promote adoption of the ecosystem approach to environmental management. The task force identified both barriers and opportunities that federal agencies face in implementing the ecosystem approach. It selected seven ecosystems as case studies: parts of the Great Lakes, the coastal Louisiana wetlands, the South Florida ecosystem, the southern Appalachian highlands, Pacific Northwest forests, Prince William Sound, and the Anacostia River watershed in metropolitan Washington, D.C. These initiatives have spurred similar efforts for other critical ecosystems stressed by climate change and human activities.

National Environmental Monitoring and Research Initiative

The ecosystem approach is a major paradigm shift. Traditionally, federal agencies have responded to their mandates by dealing with single resources, single stresses, and single issues. However, many environmental issues, including climate change, are best considered in a more integrated context. Building the knowledge base and assembling the information to support a more integrated approach is a critical priority.

The National Environmental Monitoring and Research Initiative was launched to address this need by improving the efficiency, effectiveness, comprehensiveness, and coordination of federal environmental monitoring and research networks and programs. Better integration of scientific data produced from the nation's extensive remote-sensing, inventory, survey, monitoring, and research networks will allow the simultaneous assessment of multiple resources and will contribute to a better understanding of the causes and effects of environmental change. This ability to predict how an action will affect the future health of ecosystems will allow significant advances from our current management of ecosystems and natural resources.

Working through the National Science and Technology Council's Committee on Environment and Natural Resources, the federal government is developing a national framework for an integrated monitoring and research network. By allowing comprehensive evaluation of our nation's environmental resources and its ecological systems, this national network will produce a sound scientific information base to support natural resource assessment and decision making.

Several federal partners are participating in this venture: the Departments of Agriculture, Energy, and the Interior; the Environmental Protection Agency; the National Aeronautics and Space Administration; the National Oceanic and Atmospheric Administration; and the National Science Foundation. This activity will achieve closer linkage of federal environmental monitoring and research networks and programs, which together account for $650 million in annual expenditures. An important result will be provision of information to the public on what it is getting in return for its annual investment of over $120 billion in pollution abatement and control.

Work on the National Environmental Monitoring and Research Initiative is well under way:

• A draft framework for integration has been completed and published.
• A Mid-Atlantic Regional Workshop in April 1996 laid the foundation for a pilot demonstration project beginning in 1997.
• A National Workshop in September 1996 (including representatives from state and local government, industry, nongovernmental organizations, and academic experts) endorsed the draft framework and was charged by the Vice President to develop a Report Card on the Health of the Nation's Ecosystems by 2001.
• An interagency Environmental Monitoring Steering Committee is coordinating program development and implementation, working closely with the Federal Geographic Data Committee, the Interagency Task Force on Monitoring of Water Quality, and other relevant organizations.

This initiative is a partnership with state and local governments, nongovernmental organizations, private industry, and citizens--the people whose decisions affect the nation's environment. Coordinating this nationwide effort with those of other nations, and with the major global observation programs that are now being defined and implemented, can lead to an international monitoring network capable of detecting large-scale, long-term environmental changes, such as improved responses to environmental policies or detection of changes due to climate and to other environmental or anthropogenic influences.

Research and Development

Given the current inability of experts to accurately predict the regional timing, magnitude, and consequences of change, decision makers must plan for natural and managed systems in the face of considerable uncertainty. A wide variety of anticipatory measures can be still be taken, including a broad and comprehensive research agenda to develop the understanding of the climate system needed for effective decision making on climate change issues.

In addition to a wide variety of research spanning the physical and socioeconomic sciences, extensive interdisciplinary research efforts are necessary for addressing the complex interactions of chemical, biological, ecological, and social processes that affect the climate system. In response to this need for objective information, the United States has created and sustains the U.S. Global Change Research Program, which organizes and coordinates the activities of many different federal agencies. Since its initiation in 1988, the Research Program has focused on understanding the physical climate system and projecting future global changes. (See chapter 6 for more information about the Research Program.)

As scientific understanding of the climate system has advanced, new areas of research have emerged. These include the impacts of climate change--that is, the changes in ecological and socioeconomic sectors resulting from climate change, the regional implications of such changes, how species are likely to adapt to them, and the adaptation strategies that may be useful in managing natural resources as climate changes. Promising research areas include regional-scale modeling, integrated assessment, ecosystem science, climate variability, GAP analysis for design of migration corridors, and genetic engineering of crops.

These research activities have relevance beyond climate change for managing natural resources, and in some cases have been undertaken for reasons other than climate change concerns. Yet even when they are outside the formal mechanism of the U.S. Global Change Research Program, they are providing, with little or no modification, useful information and results.

Assessing Vulnerabilities and Identifying Adaptation Strategies

Managed systems (e.g., coastal zones and range lands) are more adaptable to climate change than "lightly managed" or natural ecosystems (e.g., parks and undeveloped land) (IPCC/WMO/UNEP 1996b). For example, agriculture and water resources are vulnerable to climate change but can become highly adaptable by crop improvement and development, water conservation and desalination, and a variety of other strategies.

Natural ecosystems respond slowly and may be unable to migrate as their ideal climate range shifts north or to higher elevations. Fragmentation of the landscape (from urbanization) may also inhibit migration. The gaps in our understanding of how these natural systems are maintained or how they change make realistic response strategies difficult to identify today.

The United States is analyzing the vulnerabilities of key sectors to climate change--notably, agricultural land, water supplies, coastal areas, forests, lightly managed ecosystems, and human health. At the same time, it is developing strategies to facilitate the adaptation of these resources and systems to a changed climate. In many cases, this may involve modifying existing natural resource management strategies originally designed to cope with other environmental stresses, such as air pollution, population growth, and changes in land use.

The degree of modification needed will vary by sector. In some cases, the additional suite of stresses brought about by climate change could significantly weaken already highly stressed and fragile systems, while other systems may be more robust. In all cases, contingency planning, ecosystem management techniques, and research and development are desirable to increase resiliency and minimize the negative consequences of climate change. The strategies described in the following sections form a national aggregate of adaptation options for vulnerable sectors.

Agricultural Land

Agriculture in the United States is an intensively managed, market-based activity. Throughout the world, agriculture has adapted continuously to climate variability as it has adapted to changes in economic conditions. The American agricultural sector continues to respond to new technologies, new environmental regulations, and changes in population and market demands. Market forces are a principal catalyst for rewarding and encouraging rapid adaptation, and the domestic agricultural sector is preparing to adapt to climate change.

Vulnerability

The potential effects of climate change on agriculture are difficult to predict. Agricultural productivity is likely to be affected worldwide, which would lead to alterations in both national and multinational regions, redistributing agricultural activities and changing farming intensity. In the United States, the range over which major crops are planted could eventually shift hundreds of miles to the north. In addition to temperature shifts, the availability of fresh water and the distribution of pests and diseases may have significant impacts on production.

For American farmers, who are already facing increasingly competitive and growing world markets, any relative change in regional productivity compared with the rest of the world would signal market-driven incentives to adapt to the changes. Some individual farmers may benefit through locally improved yields or higher prices, while others may suffer because of relatively severe local climate changes requiring significant economic investment to adjust farming systems. Rapid geographical shifts in the agricultural land base, brought about by very rapid climate changes, could disrupt rural communities and associated infrastructures.

Adaptation Strategies

Climate change adds a new dimension to government efforts to improve the knowledge and skills of farmers, to encourage adoption of new technologies, and to expand the array of options available to farmers. Efforts to maintain the genetic diversity of crops and improve farm technologies will help to ensure sufficient production for an increasing population in an uncertain climate. Similarly, efforts to speed the rate at which appropriate farming systems can be adopted lower the potentially high financial and human costs of adjusting to climate change.

The past performance of the research community in developing new ways for certain crops to overcome climatic constraints suggests its substantial capacity to respond in the future. For example, through the efforts of crop breeders and agronomists, the hard red winter wheat zone has been greatly expanded since 1920 as the varieties of the crop have been effectively adapted to colder and warmer temperatures and drier conditions. The steady improvements in productivity have also been made possible by improved farm-management practices.

More recently, biotechnological methods, including new tissue-culturing and genetic-engineering tools, combined with traditional agricultural breeding methods are allowing scientists to alter plants to incorporate greater disease, insect, and weed resistance and to better withstand environmental stresses, such as cold, drought, and frost. Such precision agricultural techniques should help tailor crops to prevailing regional conditions as the climate changes.

The opportunities for adjusting to climate change are numerous. However, oversubscribed water demands in the Great Plains and the West will limit the potential for compensating adjustments. The inability to predict changes at regional and local levels makes effective response difficult to project, as does a lack of experience and knowledge about alternative crops and agricultural practices suitable for rapid adaptation to such changes.

Recent changes in U.S. agricultural policy have decoupled support payments from maintaining production of a particular crop. As a result, producers will rely more heavily on market signals and can adapt more readily to the environmental changes. Crop insurance may become increasingly costly under a harsher climate and, if not well designed, may tend to diminish the incentive for farmers to take appropriate precautionary actions to reduce their exposure to climate risks. In contrast, water-resource planning and changes in state and regional laws regarding the marketing of conserved water are already enhancing incentives for efficiently using water resources in agriculture.

The most pressing tasks that the federal government is currently undertaking with regard to agriculture and climate change are:

• Developing a nationwide telecommunications system to improve the transfer of technology and information to farmers to speed adaptation and innovation activities.
• Strengthening research, development, and pilot programs for computerized decision aids and farm- and ranch-management systems.
• Supporting research and technology that will ensure that the agricultural sector can deal successfully with the various challenges of the next century, through the continuing development of new crop varieties to meet the needs of farmers due to changes in soil water, pest, climate, and processor requirements.

New Farm Bill and Carbon Sinks . The Federal Agricultural Improvement and Reform Act of 1996 has significantly changed U.S. agricultural policy. Under the 1996 Farm Bill, farmers continue to have an opportunity to enroll their environmentally sensitive land in the Conservation Reserve Program and receive annual rental payments for taking the land out of crop production and for maintaining specific conservation practices. Farmers participating in the federal farm programs must implement conservation measures reduce soil erosion, improve water quality, enhance wildlife habitat, and increase carbon sequestration in the soil.

Under the 1996 Farm Bill, tree planting will continue under the Conservation Reserve Program, with cost-share assistance in the three Forestry, Stewardship, and Environmental Quality Incentives Programs. Tree planting under cost-share programs has averaged about 136,364 hectares (300,000 acres) a year, but is expected to decline in future years in response to lower levels of federal funding.

Research Programs. A wide range of U.S. agricultural research programs can support adaptation to climate change. Ongoing programs include the development of stress-tolerant crop varieties, strengthening of the plant germ plasm repositories and long-term germ plasm storage, the plant genome mapping program, and biological engineering research in pest resistance.

Extensive resources are being devoted to addressing how elevated atmospheric CO₂ concentrations may directly influence crop physiology, growth, yield, and water use and how elevated CO₂ levels may interact with other environmental factors and management practices. Many agricultural practices, like tillage, fertilization, and the burning of crop residue, greatly influence fluxes of greenhouse gases such as CO₂, methane, and nitrous oxide; research is being conducted to examine how climate change may alter these processes.

The U.S. Global Change Research Program is conducting research on developing management tools for responding to the potentially undesirable effects of climate change on agricultural productivity domestically and worldwide. These tools include methods for aggregating plant-scale models to predict regional-scale effects. Current research programs also focus on the needs of production systems, long- and short-term storage and post-harvest protection systems, food safety and quality, processing technologies, transportation technologies, and market systems.

Coastal Zones and Fisheries

The Intergovernmental Panel on Climate Change (IPCC) has concluded that global sea level has risen 10-25 centimeters (about 4-10 inches) during the past century and may rise a minimum of 15-95 centimeters (about 6-38 inches) by 2100, with a best estimate of 50 centimeters (20 inches) by the year 2100.

Vulnerability

The U.S. coastal zone includes thousands of square miles of undeveloped coastal wetlands, developed barrier islands, and dry mainland areas, within 1 meter (about 3 feet) of mean high water. Accelerated population growth along U.S. coasts is increasing stress on coastal systems and placing them at greater risk from potential climate change.

Rising sea level inundates low-lying areas, erodes shores, exacerbates coastal flooding, and increases the salinity of rivers, bays, and aquifers. Some areas are already experiencing rapid erosion due to such factors as subsidence, storms and hurricanes, coastal processes influenced by local geology, sediment supply, tidal range, ocean currents, weather extremes, rising relative sea level, and human-induced land-use changes. Coastal wetlands, for example, are already eroding, particularly in Louisiana and Maryland. These wetlands provide habitat for numerous species of birds, are a nursery ground for many commercial fish and shellfish, and play a role in extracting nutrients and toxic chemicals from water.

Coral reefs, are also susceptible to climate change from increased water temperatures and rising sea level. In many parts of the world reefs have undergone episodes of "bleaching" (loss of symbiotic algae) as a result of warmer local ocean temperatures. The most extreme example of these episodes was associated with the intense 1982-83 El Nino event, which killed extensive colonies of coral in the Pacific Ocean.

Commercially valuable marine fish stocks and the ecosystems that support them are also vulnerable to natural and anthropogenic changes in climate. Rising water temperatures increase risks to fish stocks already stressed by overharvesting. Fluctuations in some fish populations coincide with basin-scale physical changes in atmospheric forcing and surface ocean conditions (temperature, mixed-layer depth). In the northwest Atlantic Ocean, for example, interannual-to-interdecadal fluctuations in the physical environment and their effects on marine ecosystems are being examined as part of a larger effort to rebuild the once abundant Georges Bank cod and haddock stocks. In the northeast Pacific Ocean, salmon populations vary over decadal time scales in response to ocean-circulation changes in the California Current and the Coastal Gulf of Alaska System.

Adaptation Strategies

Adaptation strategies for coastal land loss fall broadly into four strategies:

• hard-engineering--building groins, sea walls and elevating coastal structures;
• soft engineering--nourishing beaches and stabilizing dunes;
• management options--applying (1) various development and land-use restrictions and (2) flood insurance; and
• property protection strategies --allowing individuals to protect their property.

In the case of future climate change and sea level rise, it may be more prudent to anticipate the impacts of potential sea level rise by taking action now. It is also nonetheless highly desirable to gain a better understanding of the adaptability of coastal ecosystems. Adaptation can be facilitated by identifying areas at high risk, improving understanding of the processes that build and erode shorelines, and developing integrated coastal ocean-prediction systems (see chapter 6).

Federal Coastal Zone Management Act . One strategy is to factor sea level rise and changing climate into the integrated coastal resource management programs at various governmental levels so that precautionary measures will minimize the potential damage caused by climate change. The Federal Coastal Zone Management Act requires states to consider the problems of climate change and sea level rise in their programs.

Many states have already taken considerable measures to ensure that growth in the coastal zones and the potential loss of resources will be planned for and managed accordingly. Examples include policies addressing sea level rise, setback zones, standards for infrastructure development, research, and education.

Coastal Wetlands. Coastal wetlands naturally migrate in response to changes in sediment supply and relative sea level. However, it is unknown if the rate at which wetlands migrate is sufficient to survive sea level rise. Establishing wetland reserves and protected areas adjacent to current coastal wetlands can facilitate adaptation.

Maine requires removing development to allow the landward migration of coastal wetlands in dune areas. A few states recognize "rolling easements" along ocean shores to permit natural dune systems to migrate inland. Other states have decided that protecting private property from erosion is a high priority, and guarantee landowners the right to erect a bulkhead, even though doing so results in the loss of natural shorelines.

Coordinated studies of wetland systems along the eastern Gulf of Mexico and southern Atlantic coasts and changes in the Mississippi Delta provide credible estimates of the ability of coastal wetlands to adapt to sea level rise. Other research related to the vulnerability and adaptation of coastal systems includes: space-based geodesy studies to distinguish the long-term trends in sea level change due to glacial melting and ocean expansion from effects of post-glacial rebound and active tectonics; studies that test existing geological models of coastal erosion processes; studies of coastal hypoxia; and studies of the frequency, magnitude, and tracks of storms.

In addition, the U.S. Global Change Research Program is developing and validating methods for estimating the effects of global climate change on regional fishery resources and their supporting ecosystems. This program is also examining the reproductive dynamics of the sardine, anchovy, and mackerel stocks off the coasts of California, Chile, Spain, and West Africa.

Coral Reefs. The United States is active in the Coral Reef Initiative, which promotes the conservation and sustainable use of coral reefs and related ecosystems (mangroves and sea-grass beds) within the United States and throughout the world. The initiative will integrate research, assessment, monitoring, and management of reef ecosystems through better coordination of existing activities and the creation of new programs. Among other activities, this program will focus on improving our understanding of how reef ecosystems are affected by global climate change.

Research to Improve Preparedness . A Coastal Risk Assessment Data base has been developed to integrate seven physical/land/marine variables (elevation, coastal land forms, wave height, etc.) with six climatological variables (storm frequency, surge height, etc.) to better quantify the vulnerability of U.S. coastal zones to climate change. Approximately 30 percent of the Gulf Coast and 15 percent of the East Coast were ranked as highly vulnerable to erosion or inundation.

In urbanized and high-use recreational areas, coastal beaches are nourished with imported sand and are protected by structures. However, a better understanding of the effectiveness of various beach nourishment and protection methods is needed.

Improved planning for catastrophic events, improved building codes in high-risk coastal regions, widespread public education about the risks of living in coastal zones, and limiting certain kinds of development in high-risk zones are additional adaptation strategies. Research to understand and forecast the response of living resources to climate-induced shifts will better position managers to deal with anticipated changes in fisheries and their habitats.

Water Supplies

Society depends on water for consumption, industry, transportation, and energy. Future climate change will affect water supplies unevenly, depending on regional and local weather, soils, topography, vegetation, hydrology, hydrogeology, and other factors.

Model calculations suggest increases in average global precipitation and the frequency of intense rainfall events, and a marked decrease in soil moisture over some mid-latitude continental regions during the summer (Figure 5-2). To a large extent the impact of climate change on water supplies is still unknown.

The 1994-97 period saw a significant rise in the number and scope of federal, state, and local efforts to integrate climate variability and its impacts on water supplies into the planning, design, and management of water-supply systems throughout the United States. These efforts stem from recent extreme floods and droughts and the recognition by many scientists of the likely significant impact of climate change on precipitation.

For example, the winter storms of December 1996 and January 1997 created flood conditions in several western states, disrupting water-treatment facilities and contaminating surface- and ground-water sources. More recently, in April 1997 severe floods in North Dakota dangerously contaminated drinking-water supplies in Grand Forks and the surrounding areas. Recent failures of agricultural waste-containment facilities, including farm ponds, in the eastern United States have contaminated adjacent streams and rivers that are the only sources of drinking water for communities downstream. Flooding in agricultural areas tends to increase the likelihood of the migration of pesticides into drinking-water supplies, while flooding in urban areas increases the risk of contamination by hazardous wastes.

Vulnerability

Many factors are straining U.S. water resources and leading to increased competition among a wide variety of different uses and users of water. For example, human demands for water are increasingly in conflict with the needs of natural ecosystems, degrading the quality and depleting the quantity of water. In addition, water infrastructure in many urban areas is aging. Climate change will exacerbate these problems.

Studies have been conducted to assess the vulnerability of the major U.S. river basins to flooding and drought, disruptions in water supply, hydropower reductions, ground-water overdrafts, and extreme events. Among the most vulnerable systems are those in the western United States, particularly, the Great Basin, California, Missouri, Arkansas, Texas Gulf, Rio Grande, and lower Colorado. Arid basins could experience the largest relative change in water flow from climate change. Even small reductions in water availability could be significant, may be highly expensive to remedy, and could affect the social and economic well-being of communities in those areas.

For example, reduced surface-water flow may impede or may even render current transportation routes and waste disposal practices impractical and will block the migration of fish and other water-bound species. The drawing down of ground-water levels may result in land subsidence, saltwater intrusion into freshwater aquifers, and the loss of surface-water systems and associated wetlands. Changes in hydrologic regimes may also indirectly degrade the health of ecosystems, through increased nutrient loads, eutrophication, erosion, and other processes.

At the other end of the scale, regions traditionally considered to be rich in water may experience increased demands for domestic and agricultural water uses.

Adaptation Strategies

The United States has made a firm commitment to address issues related to water supply and management within the context of ecosystem management and watershed planning. Many institutional arrangements for managing and allocating water resources have evolved over the past 150 years as agricultural, hydropower, and industrial development supported an expanding economy. Policies were designed for managing potential water scarcity, and the industrial, hydroelectric, and agricultural sectors increased the efficiency of their use of water.

Primary among the water-resource use issues is the realignment of incentives to conserve water as more efficient delivery and use systems are developed. Still, many existing predictive tools (climate, watershed, and aquatic ecosystems models) are not sufficiently developed to predict potential water shortages or potential system responses to them. Most techniques of hydrologic analysis used in water project planning are based on the assumption of an unchanging climate.

Water-resource managers need improved methods for assessing the sensitivity of the systems they manage to seasonal and longer-term variations in weather and climate. Equally important is the ongoing development of methods for evaluating the risk or uncertainty associated with such assessments. To facilitate adaptation to changes in water resources caused by climate change, the federal government, in cooperation with state and local agencies, is focusing on the following steps toward improving water-resource planning and management both to help relieve existing stresses and to prepare for climate change.

Development of New Analytical Tools and Data Bases . The U.S. Army Corps of Engineers' Economic and Environmental Principles and Guidelines for Water and Related Land Resources Implementation Studies takes long-term climate changes into consideration (USACE 1983). The Corps devised the concept of "Drought Preparedness Studies" to be used when nonstructural and nonfederal solutions are needed. It uses computer models and hydrological trends to assist in water management decision making.

The development, dissemination, and use of new modeling and forecasting tools facilitate the analysis and prediction of hydrological response to change. For example, the Army Corps' 1994 "Comprehensive Guide to Water Management Models" covers the significant hydrologic and reservoir system models used by federal governments and academia. Additionally, the U.S. Geological Survey developed a historical data base of most U.S. rivers and streams, based on stream-flow gauges unimpaired by other human-made structures. This allows regional water planners to evaluate the variability of natural stream flows.

Adoption of Demand-Management and Water-Conservation Practices . The Energy Policy Act of 1992 requires each federal agency to implement by 2005 all water-conservation measures that have a payback period of ten years or less. The interagency Western Water Policy Review Council was created to study and advise the nineteen semi-arid western states on implementing these measures, including the "water banks" that Arizona, California, Idaho, and Oregon have created to facilitate the storage, transfer, and distribution of water.

In 1993, following the Interagency Floodplain Management Review Committee (the "Galloway Commission") report on the 1993 Mississippi floods, the U.S. government created the Flood Plain Management Task Force. The task force assessed flood damages and attempted to create a balance among natural and human uses of flood plains and their related watersheds that would meet the nation's social and environmental goals. An interagency review of the task force envisions future flood plain use in which human activity is attuned to flood cycles. For example:

• Development in commonly flooded areas would be curtailed and gradually replaced with recreational areas.
• Critical infrastructure, such as roadways and water-treatment facilities, would be elevated, protected, or otherwise designed to withstand floods.
• Larger urban areas would remain protected behind large levees, but would incur a greater proportion of expenses for maintenance.
• Science and technology would better assist water planning through a wide range of mechanisms, from creating a computerized data base of flood-prone structures to developing hydrological, hydraulic, and meteorological models.

Basinwide Management of Reservoirs . The 1995 Bureau of Reclamation-State of Texas Memo of Understanding commits the Tennessee Valley Authority and the upper Colorado River system to cooperate to provide local water users with technical assistance and other support necessary to implement statewide practices to improve water quality and availability. By operating reservoirs within the same basin as a single system, rather than individually, the two programs will greatly enhance the efficiency and flexibility of their operations.

Improved Information and Models . Many studies are designed to develop the capability of predicting the hydrometeorological and water resource responses to climate variability and change across the range of environmental conditions existing in the United States. Evaluation of water planning and decision making in a number of studies incorporates IPCC models into regional water supply assessments. These studies quantify and predict hydrological changes resulting from various IPCC model scenarios, highlight areas for improvement in global circulation models, and reveal potential sensitivities in regional water systems that could cause future concern. The U.S. Global Change Research Program is supporting multidisciplinary studies for creating regional "mesoscale" climate models that can predict the impacts of climate change on water supplies, wetlands, fisheries, and hydropower (see chapter 6).

"Lightly Managed" Ecosystems

Effective ecosystem management recognizes the importance of understanding how each of the living and nonliving parts of an ecosystem contributes to, and is affected by, the functioning of the whole system and how the system responds to stress. "Lightly managed" ecosystems are those natural systems with little or no direct management in comparison to agricultural and urban lands. They include wilderness areas, preserves, wetlands, national parks and wildlife refuges, some coastal systems, alpine tundra, and some economically marginal forests.

Vulnerability

Certain characteristics of small, "lightly managed" ecosystems--such as being isolated or fragmented, containing sensitive species, or already experiencing considerable stress from pollution and geographic fragmentation--make them extremely vulnerable to climate change. Changes in the availability and quality of surface and ground water and in atmospheric deposition may further strain the function and limit the productivity of ecosystems.

Federally protected natural areas have become repositories for some of the nation's rarest species. However, these areas are subject to increased stresses from activities that occur both within and outside their boundaries. Climate change may realign the geographical environmental boundaries of these natural areas, while the boundaries that define their management and degree of protection remain fixed. As a result, some areas may become incapable of providing the benefits or serving the functions for which they were originally established, such as maintaining their unique or distinctive character, protecting rare species and other biological resources, and maintaining the quality and availability of other services, such as nature study or recreation.

Overall, as much as 80 percent of the land in the United States may shift to a new vegetation zone. If climate change accelerates habitat change or proceeds so rapidly that some species cannot adapt quickly enough, the rate of extinction of species may rise, and overall biodiversity may decline. Isolated species may find themselves in climate zones no longer suitable for their survival.

Some of the most vulnerable ecosystems are in the currently dry continental interior, where climate change models predict aridity will increase significantly. Vegetation on coastal margins may also be at risk from the flooding and saltwater intrusion accompanying rising sea levels, or from increases in damaging storms. Plant communities with small or highly fragmented ranges may be lost, such as those at the upper elevations of mountains with no clearly discernible migration routes.

While evidence of the survival of pockets of temperate species from previous ice ages indicates that these glacial relic communities may survive radical climate change, models are not sufficiently sophisticated to enable scientists to predict future events in forest communities. For example, some natural forest ecosystems may rotate rapidly through a change in dominant canopy species, similar to the disappearance of the American chestnut from the forest canopy in the 1920s. Certain species and unique populations will most likely become isolated if climate change is too rapid. In many cases, adaptation will depend on the availability of a wide gene pool within the species.

Adaptation Strategies

The ability of humans to protect natural areas and biodiversity from large-scale climate change is currently limited. For example, little information exists about the probable timing, rate, or geographical extent of climate change. Likewise, there is limited understanding about which species are most sensitive to climate change, which could be saved, how to restore habitats or entire ecosystems, and what lands will be most valuable as preserves under varying climate change scenarios.

To facilitate adaptations to climate change in natural areas, the U.S. government is coordinating large-scale information gathering efforts (including research, inventory, and monitoring options) and is evaluating management measures. Research is being coordinated on species' sensitivity to climate change, restoration and translocation ecology, the design and effectiveness of migratory corridors or protective buffer zones, the development of ecological models, and the effects of elevated CO₂ concentrations on plants and animals.

The 1995 publication of the Global Biodiversity Assessment, to which the United States was a major contributor, provides an unprecedented baseline of information against which the impacts of climate change on species can be monitored (Heywood and Watson 1995). Under the U.S. Global Change Research Program, contributing research on the adaptation of natural ecosystems to global change includes forest health monitoring; studies on threatened, endangered, and sensitive species; and research into the physiological basis of resistance to drought, ultraviolet radiation, and other stresses.

Through its Man and the Biosphere Program, the United States is also assisting in the development of the Biosphere Reserve Integrated Monitoring Network in Europe and North America. This pilot program establishes electronic linkages among the 170 biosphere reserves in Europe and North America for monitoring biodiversity and global change. If the program is successful, it will serve as a model for other biosphere reserves throughout the world.

Ecological Research and Assessment . U.S. agencies are developing programs to fill key gaps in the understanding of ecosystem functions and how they may be protected, restored, and enhanced at small spatial scales. Agency programs include:

• The U.S. Environmental Protection Agency's Environmental Monitoring and Assessment Program --Estimates the current condition of U.S. ecological resources, monitors indicators of pollutant exposure and habitat, and provides ecological status and trends reports to managers and the public.
• The U.S. Fish and Wildlife Service's Gap Analysis Project --Aims to prevent species extinctions by promoting protection of species-rich areas and unprotected vegetation types before they are threatened.
• The National Science Foundation's Long-Term Ecological Research Program--Focuses on eighteen sites and five core research categories, measuring such traits as primary productivity, nutrient cycling, site disturbance, population distribution, and accumulation of organic matter. The spatial and temporal scales of these processes--decades to centuries--make this program's activities especially important for climate change and adaptation-related research.
• The National Park Service's series of research programs in Glacier, Rocky Mountain, Sequoia, and several other parks --Assesses the impacts of climate change and plans for potential adaptation. In Rocky Mountain National Park, a regional hydroecological simulation system, linked with a general circulation model, was used to simulate weather and climate change over the Rocky Mountain States and relate future climate to ecosystem changes. Through coordinated field and modeling studies, researchers have shown the forest-tundra mountain ecotone is spatially heterogeneous and can be extremely vulnerable to climate change, yielding specific levels of sensitivity to different stresses for patch forest, closed forest and krummholz habitats. These data allow park managers to plan adaptive strategies for short- and long-term park management.

In addition to these agency programs, a partnership of seven federal agencies is contributing to this ecosystem research and assessment effort through a National Environmental Monitoring and Research Initiative, which will provide a comprehensive evaluation of our nation's environmental resources and its ecological systems. This, in turn, will produce a sound scientific information base to support natural resource assessment and decision making.

Forests

Forests cover roughly one-third of the U.S. land area and more than 40 percent of the eastern portion of the country. They shape much of the natural and urban environment and provide the basis for a substantial forest products industry.

Over historical and long-term ecological time scales, forest ecosystems and the major species of trees that comprise them are extremely susceptible to climate change. Forests have shifted distributions in response to natural climate changes, often with a reassembly of species into a community of tree species completely unlike any known today.

One of the greatest concerns is that the human-induced build-up of greenhouse gases in the atmosphere will drive climate changes that are many times more rapid than naturally occurring past changes. Many tree species may be unable to migrate fast enough in response to projected changes in precipitation and temperature, especially at the southern margins of major biomes. The 1995 IPCC report estimated that roughly one-third of the world's tree species will change their distribution in a world where carbon dioxide concentrations are double preindustrial levels (IPCC 1995b).

Vulnerability

If the climatic regime of forest species changes significantly, they could suffer declining growth rates and increased mortality from temperature, moisture, and drought stresses, and increased damage from insects, disease, and fires. Climate change may shift the optimum growing range for some North American forest species a great distance from their current range, over a relatively short period of time. Such a shift would almost certainly exceed the ability of less intensively managed forests to migrate.

It is not yet known how different species may respond to conditions found outside their current ranges, or even if the current ranges are optimal for each species. Some research suggests that various species may be more adaptable to climate changes than their current range indicates. Some plants' responses are caused by differential effects of climate on the growth and regeneration of locally abundant species and genotypes; for other plants, climate change facilitates plant migration resulting in a new geographical distribution.

Terrestrial biomes will not react to climate change en masse. Individual tree species respond to climate changes at widely different rates. For example, woody species dominating temperate forests typically shift ranges as slowly as 50-400 meters (55-437 yards) a year. In contrast, the IPCC emission scenarios estimate rates of climatic change over the next century that would necessitate forests to migrate 150-550 kilometers (250-915 miles) northwards, or 150-550 meters (164-601 yards) higher in elevation to stay within the same climate zone. These predicted rates are more than ten times faster than previously documented rates of migrations if an elevation gradient is not available.

The spread of tree species is often limited by the rate of seed dispersal and by the availability of appropriate soil moisture and other habitat conditions. Human development has greatly diminished the number of sites available for species to recolonize in response to human-driven climate changes and may create insurmountable barriers for many species' migrations.

Forests in locations already subject to droughts, fire, and wind damage will be highly vulnerable to depopulation or to changes in species composition and community structure if the frequency or intensity of these stressors increases. In boreal forests and tundra ecosystems, the release of CO₂ from permafrost soils due to a rise in annual temperatures could change these biomes from net sinks to net sources of carbon.

Elevated CO₂ levels, and the increases in the efficiency of water use that attend those levels, may raise the productivity of some forests, though it is unknown how large or prolonged the effect will be over long time frames. Some estimates developed through carbon flux models suggest that growth increases of 16 percent or more may accrue by the time CO₂ emissions double. However, the rate of carbon uptake by forests will not be linear, and limited soil nutrients may prevent such increases. Other effects of climate change--water shortages, pest activity, and fires--may also effectively decrease net primary productivity and may affect the distributions of forest types.

Adaptation Strategies

Government intervention to facilitate adaptation over short time frames may at present be impractical or limited. Even timber-industry forests are not intensively managed by the standards of annual agricultural crops. Furthermore, on large areas of public forest lands, such as wilderness areas, even a minimal management response may itself be viewed as incompatible with the goals for which the forests are held. Focusing forest management on sustaining ecosystem structure and function will promote future forest productivity, health, and diversity in the face of such stresses as climate change.

The federal government is considering several programs to mitigate negative impacts as U.S. forests respond to long-term changes in climate. Research focusing on the development of high-quality forest product species continues to develop suites of varieties adapted to greater levels of stress, both in the West as well as in the Southeast. Studies are under way to determine how changes in atmospheric chemistry affect tree growth and how to increase the U.S. carbon sink. Application of modern forestry practices to reduce damage due to harvesting and substitution of nontimber products are also potential adaptation options.

A national effort to collect and conserve a wide variety of forest species' seeds would ensure that the means are available to respond to the potential loss of forest species or populations due to climate change. Some arboretums, universities, and U.S. Forest Service researchers already have limited programs associated with threatened or endangered forest species. However, an expanded and enhanced forest seed bank program with forest genetics research would greatly help the process. Seed collections should represent the variety of genotypes for each species. While maintaining the large quantities of seeds needed for a major replanting would be an unrealistically costly goal, the systematic storage of seeds would be valuable to commercial tree breeding and for biotechnology efforts in tree improvement.

Given the evidence that northern forests may be accumulating carbon from the atmosphere, one idea under intensive study is that of "afforestation"--planting additional forest lands to counterbalance the emission-based atmospheric input. The U.S. Department of Agriculture's Forest Service has provided a range of working estimates on how much carbon various forests in the United States will take up over the next fifty to one hundred years. It has concluded that significant amounts of currently poorly stocked forest land could be afforested for increased carbon sequestration. Ameliorating the social pressures that drive the conversion of forests to developed and urban uses may further reduce CO₂ emissions from deforestation.

Several prerequisites need to be addressed before any new adaptive measures are undertaken in the field of forestry. These include (1) a better understanding of the role of forests in the overall global carbon cycle; (2) the response of various forest species to rapid climate change, drought and flooding, and other environmental stresses; and (3) better monitoring methods to track the growth and decline of U.S. modern forests. Toward these goals, intensive studies of carbon cycling are being conducted using newly developed carbon models and field experiments of carbon fluxes in different terrestrial settings. And better models are being developed for predicting the responses of forest species to climate change. Retrospective studies of historical forest distribution shifts are helping to validate these models.

Human Health and Climate Change

Several expert bodies, including the IPCC and the World Health Organization, have expressed a growing concern about the potential adverse effects of climate change on human health. The IPCC has concluded that these effects will be diverse and will occur via direct and indirect pathways. These conclusions are based on information on scientific relationships between climate and human health; relatively few quantitative studies have applied these relationships to projected climate changes.

There are great difficulties in estimating potential health outcomes due to climate change. Some aspects of climate change will most likely lie outside the range of recorded human health experience, and the ability of models to project regional climate changes is still limited. Moreover, it is imperative to view the impacts of climate change on infectious diseases within the context of other key determinants of disease.

Human populations differ greatly in their environmental circumstances, social resources, and preexisting health status and, therefore, in their vulnerability to climate-induced stress. For example, the number of additional cases of disease due to a climate-related increase in potential transmission would depend on prior contact with the disease (i.e., immune status of the population), general biological resilience, (e.g., nutritional status of the population), population density, and patterns of interpersonal contact. Social and public health infrastructure and health-care resources will also mitigate the impact.

In addition, the control of certain diseases is becoming more difficult due to increases in antibiotic and drug resistance and decreases in the effectiveness of vector control methods (e.g., increasing pesticide resistance). Many of these factors are changing over time, so it is inevitably difficult to assess the health impacts of climate change.

Vulnerability

Heat-related Mortality. Climate change is expected to increase the frequency and intensity of extremely hot days, which may increase the number of heat-related deaths. Research on forty-four U.S. cities found that excess heat-related mortality could increase by 70-150 percent over an estimated baseline of about 1,800 deaths, even if the population acclimates somewhat to warmer temperatures. This estimate did not account for increased use of air conditioning or population growth. While decreases in winter cold-related deaths are also expected with a general warming, research to date suggests that these decreases may only partly offset the increases in heat-related mortality.

Infectious Diseases. Climate affects infectious microbes and the insects and animals that carry them, and is a major factor in the geographic range of most disease vectors. Fluctuations in local weather conditions often determine the timing and intensity of disease outbreaks. In addition, the effects of climate on regional vegetation and food supplies, animals, and ecological relationships may also indirectly increase risks of and susceptibility to certain diseases.

Climate change is expected to result in a net increase in the geographic distribution of disease vectors and to change the life-cycle dynamics of both vectors and infectious agents. As a result, the potential transmission of many vector-borne diseases is likely to increase. Globally, the population living within a potential malaria transmission zone could increase from 45 to 60 percent by 2100, with a possible 50-80 million additional malaria cases relative to an assumed annual baseline of 500 million cases.

Air Pollution Health Risks . Degraded air quality has been associated with respiratory illnesses, aggravation of existing cardiovascular disease, and premature death.

The influence of meteorological conditions, particularly temperature, on ozone concentrations has been well established. The relatively high ozone levels in 1988 and 1995 were most likely due in part to the hot, dry, stagnant conditions that occurred in some areas of the country. In 1995, about 71 million people lived in counties with air quality that did not meet the health-based ozone standard.

Other pollutants that involve atmospheric reactions may also depend in part on meteorological variables. Changes in regional temperature, precipitation patterns, clouds, wind speed and direction, and atmospheric water vapor--all of which depend on climate--may affect future levels of air pollution.

Adaptation Strategies

To confront these complex health threats, the Administration has taken a series of bold, innovative policy actions, through the National Science and Technology Council (NSTC) Directive. In 1995, NSTC published Infectious Diseases--A Global Health Threat and held a conference on Human Health and Climate Change. And in 1996, NTSC and the National Academy of Sciences published the second report in a series entitled Proceedings of the Conference on Human Health and Global Climate Change (NTSC/NAS 1996). Among the most important policy goals presented in these reports are to:

• Strengthen domestic infectious disease surveillance and response systems at federal, state, and local levels.
• Establish a global infectious disease surveillance response system.
• Strengthen research activities to improve diagnostics, treatment, and prevention.
• Ensure availability of drugs, vaccines, and diagnostic tests.
• Expand missions and establish authority of relevant U.S. agencies to contribute to a worldwide network.
• Promote public awareness of emerging infectious diseases.

These activities are being coordinated at the highest levels of the U.S. government through an Executive Order on Emerging Infectious Diseases, with leadership from the Centers for Disease Control and Prevention and the National Institutes of Health. ~~