Реферат: Climate change
In a report synthesizing its second assessment and focusing on the relevance of its scientific analyses to the ultimate objective of the Convention, the IPCC concluded:
· Human activities--including the burning of fossil fuels, land use, and agriculture--are changing the atmospheric composition. Taken together, they are projected to lead to changes in global and regional climate and climate-related parameters, such as temperature, precipitation, and soil moisture.
· Some human communities--particularly those with limited access to mitigating technologies--are becoming more vulnerable to natural hazards and can be expected to suffer significantly from the impacts of climate-related changes, such as high-temperature events, floods, and droughts, potentially resulting in fires, pest outbreaks, ecosystem loss, and an overall reduction in the level of primary productivity.
The IPCC also concluded that, given the current trends in emissions, global concentrations of greenhouse gases are likely to grow significantly through the next century and beyond, and the adverse impacts from these changes will become greater. The remainder of this report seeks to elucidate the programs, policies, and measures being taken in the United States to begin moving away from this trend of increasing emissions, and to help move the world away from the trend of globally increasing concentrations of greenhouse gases.
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Principal Conclusions of the IPCC's Second Assessment Report While the basic facts about the science of climate have been understood and broadly accepted for years, new information is steadily emerging--and influencing the policy process. In 1995, the IPCC released its Second Assessment Report, which not only validated most of the IPCC's earlier findings, but because of the considerable new work that had been undertaken during the five years since its previous full-scale assessment, broke new ground. The report is divided into three sections: physical sciences related to climate impacts; adaptation and mitigation responses; and cross-cutting issues, including economics and social sciences. The Climate Science · Human activities are changing the atmospheric concentrations and distributions of greenhouse gases and aerosols. · Global average temperatures have increased about 0.3-0.6°C (about 0.5-1.0°F) over the last century. · The ability of climate models to simulate observed trends has improved--although there is still considerable regional uncertainty with regard to changes. · The balance of evidence suggests there is a discernible human influence on global climate. · Aerosol sulfates (a component of acid rain) offset some of the warming by greenhouse gases. · The IPCC mid-range scenario projects an increase of 2.0°C (3.7°F) by 2100 (with a range of 1.0-3.5°C (about 1.8-6.3°F). · The average global warming projected in the IPCC mid-range scenario is greater than any seen in the last ten thousand years. · Sea level is projected to rise (due to thermal expansion of the oceans, and melting of glaciers and ice sheets) by 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.