global emissions must begin declining steeply during the second quarter of the next century (Figure 3).

The results that give us cause for concern come from numerous studies of past climate change, from observations of ecosystems changing over time, and from model simulations that project future conditions. An important aspect of interpreting such results, especially model simulations, is accounting for uncertainty, which is often done in a very selective way by climate change skeptics. Uncertainty cuts both ways: outcomes could be less dramatic than expected based on our current understanding, but could just as well be more severe. We must remember that the current generation of impact projections is focused on a limited number of variables, and that this may result in an overly benign picture of the future.

For instance, a series of projections that includes carbon dioxide increases, temperature change, and precipitation changes now indicate that while there might be no "net" effect on global agricultural productivity, significant regional dislocations are expected, with the poorest countries experiencing the greatest losses. However, these analyses do not include potential water constraints or changes in the distribution of pests. As the scientists told us at the White House Conference on Climate Change last October 6, the impacts we have not been able to include are more likely to make the net results worse rather than better.

Further, climate change may not occur gradually. Most climate model simulations to date have assumed that climate will change relatively steadily as a result of human-induced emissions of greenhouse gases. Over the past few decades, however, there have been some indications that this might not be the case -- that instead climate might change in abrupt jumps.

Past climate conditions reconstructed from ice core records in Greenland, from ocean sediment cores in the neighboring oceanic regions, and from pollen records on land areas bordering the North Atlantic have found that climates of the past have changed dramatically over very short periods of time -- namely, over a few decades or even less. We have discovered that the apparent mechanism for the climate shifts is change in the large-scale ocean circulation of the North Atlantic (which is coupled to the circulation for much of the world). The evidence shows that in the past, the Gulf Stream has basically stopped carrying heat northward, causing significant cooling in Europe and northeastern North America. The risk of such a catastrophe exists but has been little studied; similarly the potential for abrupt sea level rise from collapse of the West Antarctic ice sheet or runaway warming from dramatic heating of the polar regions and subsequent release of methane cannot be ruled out.

If we do not alter our emissions trajectory, we will pass atmospheric concentrations of double the pre-industrial level by the middle of the next century, on the way toward a tripling, or even quadrupling. We could very well take the planet to levels that have not been seen for 50 million years in a single century, a geological blink of an eye. The Administration has received letters signed by thousands of scientists in the last few months urging action on this issue -

warning that nonlinearities or unexpected events, such as the Antarctic ozone hole, are more likely when rates of change are very fast.

We have received similar letters urging action from the economic community. They point out that paced actions can reduce costs and buy insurance against climate change. It is important to point out that the challenge of climate change poses a tremendous opportunity for American industry. It is absolutely clear that more benign technologies must begin replacing existing energy and agricultural technologies and practices, the primary causes of global climate change. Technological innovation is the key to our response to the climate challenge, and technological innovation is among America's greatest strengths. Reducing emissions requires development of clean sources of power and more efficient machines, structures, and industrial processes. There will be ancillary benefits of reduced air pollution and increased energy security at the same time. The consequences of our near-term technology choices are significant and long lasting. An appliance or an automobile lasts about 15 years, residential and commercial buildings are designed to last 20-30 years or more and power plants last 30-40 years.

In developing countries, there is a $100 billion annual market in energy supply technologies alone. Setting emission targets, providing economic incentives, and investing in research will spur the process of innovation and development of cost-effective technologies needed to address this problem and benefit the economy both here and abroad. The longer we continue "business as usual," the longer we delay the development and deployment of technologies that could provide a major competitive advantage to the U.S. in the 21st century. The time to begin investment and innovation is now. Let us unleash the power of American ingenuity and entrepreneurship to solve this problem and prove once again that environmental quality and economic prosperity go hand in hand.

Shifting the Focus of the U. S. Global Change Research Program

Until recently, the U. S. Global Change Research Program (USGCRP) has focused on observing and documenting change in the Earth's physical systems and understanding why these changes are occurring. It is now appropriately shifting from a nearly exclusive focus on physical systems to a much broader effort to understand what global change means for the Earth's biological systems and for the human societies that are dependent upon them. Even with aggressive actions implemented today to reduce future climate change, some further change is inevitable in Earth's climate. The USGCRP is currently focusing on how these climatic changes will impact the various regions of the U.S., and how we can best adapt to these changes and prepare for the future. In particular, we want to accomplish two things. First, we need to move from the global to the regional level to understand what impacts are likely to result from climate change both on its own and in concert with all the other human-induced stresses we are placing on the environment, such as pollution and resource extraction. Second, we must now move to approaches that are designed to achieve an integrated understanding not only of the nature and extent of physical and biological effects, but of their ramifications for our social and economic systems.

In the past year, the USGCRP established several new activities to address these critical concerns. In cooperation with OSTP, the program is sponsoring a series of regional workshops, the purpose of which is to examine the vulnerabilities to climate change and variability that are unique to each area. A table of these workshops is attached. This information will then be aggregated across regions to support the first National Assessment of the Consequences of Climate Change for the U.S., as called for by the U. S. Global Change Research Act. During 1997, the leaders of our workshops, stakeholders with a broad range of interests, and members of the scientific community have worked together to develop a blueprint for a national assessment process that examines the vulnerabilities of the United States, its ecosystems, major economic system sectors, and its social infrastructure to climate variability and climate change. A National Forum on Climate Change Impacts was held on November 12-13, in Washington, D.C. to integrate results obtained so far and continue the process of defining the National Assessment. We expect the assessment activity to take place over the next two years, with a major report issued in 1999.

Regional Vulnerabilities in the U.S.

The reports from our regional workshops provide a set of compelling statements on U. S. regional vulnerabilities, and further examine possible adaptation options. In particular, the workshops have examined how we might best cope with current environmental stresses in light of future climate change.

Alaska: The state's economic dependence on natural resources makes it highly vulnerable to climate change. Global warming will be most pronounced in northern regions. Probable consequences include drying of Alaska's interior, inundation of fragile coastal delta areas, and, most seriously, melting of permafrost, which is already underway. Continuation of Alaskan warming will lead to the disappearance of most discontinuous permafrost over the next 100 years. In many places, ground level can collapse 5 yards or more, leading to significant damages to ecosystems and human infrastructure. Houses, roads, airports, military installations, pipelines, and any other facility built on ice-rich permafrost are at risk. The melting of permafrost and the warming of tundra will lead to the release of carbon and methane deposits from the formerly frozen lands, which could make them an additional source of atmospheric greenhouse gases. Ecosystem effects include destruction of trees and caribou habitat; clogging of salmon spawning streams; reduction in forested areas; expansion of lakes and wetlands; and increased rates of coastal and riverbank erosion, slope instability, landslides and erosion.

Pacific Northwest: The dependence of the Northwest on reliable water supplies provides this region's most significant vulnerability to climate change. Model projections indicate that regional consequences of warming are likely to include changing patterns of precipitation and drought, timing of runoff, and increased inundation of coastal areas due to sea level rise. Peak runoff would come earlier in the spring because of more rain and less winter snow. Late winterearly spring flows would be enhanced, increasing the chance of spring flooding. Survival of

be reduced summer and early fall flow, particularly west of the Cascades Mountain range, due to the warmer, drier summers. This will hurt western salmon migration and spawning. In the Columbia River basin, where an overall decrease in annual run-off is likely, competition among hydropower production, fisheries protection, and irrigation will probably increase. Coastal erosion, landslides and bluff failures are also major risks to ecosystems, urban centers, and coastal development. Existing wetlands will disappear faster than new ones appear, leading to loss of coastal habitat for outmigrating salmon, spawning oceanic species, and mammals and seabirds.

Great Plains: All sectors of life in the Great Plains are dependent on a very limited water supply, and water shortages there are already a problem. The further drying expected from climate change poses the region's most significant risk. Agriculture is the base of the economy, despite the constraints of the dry and variable environment. Because agricultural water needs often exceed rainfall, water for irrigation is commonly supplied from deep aquifers, which are experiencing overdrafts and dropping water tables. As climate change leads to warmer conditions and an intensified hydrological system, the soils of the area are anticipated to further dry. The simultaneous drop in aquifer levels, greater run-off from extreme downpours, and shorter duration of snow cover will exacerbate the region's water supply problems. Drier soils could be subject to increased wind erosion, which has led to "dust bowl" conditions in the past. Better soil tillage practices would simultaneously improve soil fertility, soil carbon storage capacity, and soil moisture holding capacity. Native species will face increasing levels of competition from introduced species, such as cheat grass, Japanese brome, Russian thistle, and leafy spurge, which already account for extensive economic losses. Riparian areas (wetlands and prairie potholes), which are used intensively by hunters, anglers, and bird watchers, are extremely vulnerable to warmer, drier climate.

Southeast: The Southeast is a region of abundance, with numerous wetlands, an extensive coastline, and productive agriculture, fisheries, and forestry. Urbanization and rapid population growth are already exerting significant stress on some fragile ecosystems. The Florida Everglades have been significantly altered by human encroachment, with approximately half of the ecosystem lost or severely altered by drainage for development as well as pollution from agricultural run-off. While the Southeast's long coastline makes it a recreational playground, its low elevation renders it extremely vulnerable to sea level rise and storm surges during extreme weather events, such as hurricanes, which are expected to worsen with climate change. A foot rise in sea-level, the best estimate over the next century, could erode 100 to 1000 feet of Florida beaches, damaging property as well as tourist interests.

Southwest: Rapid population growth in this arid or semi-arid region make the Southwest extremely vulnerable to water supply problems that are likely to worsen under climate change. The region is naturally subject to large climate fluctuations, which have produced fairly robust adaptation mechanisms in ranching and agriculture. The native flora and fauna are also well adapted to life in this harsh and dry environment. Surface water supplies are insufficient; forcing reliance on groundwater, use of which already exceeds recharge and is leading to subsidence in

many areas. Climate change will pose serious challenges and is likely to result in significant impacts to the region's traditional economic sectors as well as tourism, development, and retail sectors that now make up much of the region's economy. Expected conditions include more extremely hot days, fewer cool days, and decreased winter precipitation. Alteration of the region's hydrologic cycle would affect quantity and quality of the water supply, with major implications for continued development in the region. Significant changes in vegetation are also predicted, with Gambel oak, Piñon pine, and Douglas fir largely disappearing from the region. Saguaro would die off in its current range, but might find a new home further east and at higher elevations.

New England: New England's economy is diverse, and many aspects are indirectly dependent on climate. Its natural areas are prized, and its fall foliage draws visitors from all over the world. The region is vulnerable to drought and severe storms, which modify its vegetation and impact production of forest and fisheries products. Warmer, drier climate could reduce ski tourism and shift optimal climatic conditions north into Canada for the tree species prized for their fall foliage and maple syrup. Coastal areas are likely to be affected by intensifying storms, sea level rise, and reduced freshwater input to estuaries. Air quality, already poor in the region's major urban areas, could decline even further as hot, humid weather increases, leading to increased incidences of respiratory illness.

Sectoral Vulnerabilities and Impacts

The USGCRP is also developing an extensive body of research that suggests that human health and ecological systems are vulnerable to climate change. The human-induced climate changes that are expected will add important new stresses on ecological and socioeconomic systems that are already affected by pollution and increasing resource extraction. The degree of vulnerability, and the amount and rate of change that is experienced in addition to existing stresses will determine the magnitude of climate change impacts.

Health Effects: According to the World Health Organization, the vulnerability of human populations to climate change varies across populations depending on environmental circumstances, social resources, and preexisting health status. In general, developing countries are more vulnerable to climate change than developed countries because of their limited capital and their greater dependence on natural resources. Climate change increases the risk of heatrelated mortality and the potential for the spread of vector-borne diseases, such as malaria, dengue and yellow fever, and encephalitis, and non-vector borne diseases such as cholera and salmonellosis. The incidence of infectious diseases, which are still the world's leading cause of fatalities, may also increase.

A study of deaths associated with summer time heat stress and winter time illnesses in 44 U.S. cities estimated that climate change could double the number of weather-related deaths. The elderly are at greatest risk in the U.S., and urban populations in developing countries are also especially vulnerable to heat stress.

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