Climate change — страница 5

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about 50 centimeters (20 inches) by 2100, with a range of 15-95 centimeters (about 6-38 inches). Even after a stabilization of greenhouse gas concentrations, temperatures would continue to increase for several decades, and sea level would continue to rise for centuries. Vulnerability, Likely Impacts, and Possible Responses Climate change is likely to have wide-ranging and mostly adverse effects on human health. Direct and indirect effects can be expected to lead to increased mortality. Coastal infrastructure is likely to be extremely vulnerable. A 50-centimeter (20-inch) rise in sea level would place approximately 120 million people at risk. Natural and managed ecosystems are also at risk: forests, agricultural areas, and aquatic and marine life are all susceptible. However,

adaptation and mitigation options are numerous. Significant reductions in net greenhouse gas emissions are technically possible and can be economically feasible, using an extensive array of technologies and policy measures that accelerate technology development, diffusion, and transfer. Socioeconomic Issues Early mitigation may increase flexibility in moving toward a stabilization of atmospheric concentrations of greenhouse gases. Economic risks of rapid abatement must be balanced against risks of delay. Significant "no regrets" opportunities are available in most countries. Next steps must recognize equity considerations. Costs of stabilization of emissions at 1990 levels in OECD countries could range considerably (from a gain of $60 billion to a loss of about $240

billion) over the next several decades. National Circumstances In responding to the threat of global climate change, U.S. policymakers must consider the special circumstances created by a unique blend of challenges and opportunities. The National Circumstances chapter of this report attempts to explain the particular situation in the United States--including its climate, natural resources, population trends, economy, energy mix, and political system--as a backdrop for understanding the U.S. perspective on global climate change. The United States is unusual in that it encompasses a wide variety of climate conditions within its borders, from subtropical to tundra. This diversity complicates the discussion of impacts of global climate change within the United States because those

impacts would vary widely. This diversity also adds to U.S. emission levels, as heating and cooling demands drive up emissions. Recent record levels of precipitation--both in snowfall and rain--consistent with what could be expected under a changed climate, have raised the awareness of climate impacts at the local and regional levels, and may make it somewhat easier to predict the effects of increased precipitation. The United States also is uncommonly rich in land resources, both in extent and diversity. U.S. land area totals about 931 million hectares (2.3 billion acres), including grassland pasture and range, forest, and cropland. Forested land has been increasing, while grasslands and croplands are slowly declining and being converted to other uses. The decline in wetlands

has slowed significantly as a result of the "no net loss" policy being implemented. With just over 265 million people, the United States is the third most populous country in the world, although population density varies widely throughout the country, and is generally very low. Although population increase is moderate from a global perspective, it is high relative to the average for all industrialized countries. Moreover, the number of households is growing rapidly. These and other factors drive U.S. emissions to higher per capita rates than those in most other countries with higher population densities, smaller land areas, or more concentrated distribution of resources to population centers. The U.S. market economy is based on property rights and a reliance on the

efficiency of the market as a means of allocating resources. The government plays a key role in addressing market failures and promoting social welfare, including through the imposition of regulations on pollutants and the protection of property rights, but is cautious in its interventions. Thus, the infrastructure exists to limit emissions of greenhouse gases--although the strong political and economic preference is to undertake such controls through flexible and cost-effective programs, including voluntary programs and market instruments, where appropriate. U.S. economic growth averaged 3 percent annually from 1960 to 1993, and employment nearly tripled as the overall labor force participation rate rose to 66 percent. The service sector--which includes communications,