Реферат: Climate change

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, utilities, finance, insurance, and real estate--has grown rapidly, and now accounts for more than 36 percent of the economy. The increasing role of trade in the U.S. economy heightens concerns about the competitiveness effects of climate policies.

During the 1980s, the U.S. budget deficit grew rapidly, as did the ratio of debt to gross domestic product, and a political consensus emerged on the goal of a balanced budget. The result is a tighter federal budget with many competing priorities.

The United States is the world's largest energy producer and consumer. Abundant resources of all fossil fuels have contributed to low prices and specialization in relatively energy-intensive activities. Energy consumption has nearly doubled since 1960, and would have grown far more, because of growth in the economy, population, and transportation needs, had it not been for impressive reductions in U.S. energy intensity. Industrial energy intensity has declined most markedly, due to structural shifts and efficiency improvements. In the residential and commercial sectors, efficiency improvements largely offset the growth in the number and size of both residential and commercial buildings. Likewise, in the transportation sector, efficiency moderated the rise in total fuel consumption from 1973 to 1995 to only 26 percent, despite dramatic increases in both the number of vehicles and the distances they are driven. Fossil fuel prices below levels assumed in the 1993 Climate Change Action Plan, however, have contributed to the unexpectedly large growth in U.S. emissions.

While unique national circumstances point to the reasons for the current levels (and increases) in U.S. emissions, they also suggest the potential for emission reductions. Successful government and private-sector programs are beginning to exploit some of the inefficiencies in the manufacturing sector. The development of new, climate-friendly technologies is a rapidly growing industry, with significant long-term potential for domestic and international emission reductions.

Greenhouse Gas Inventory

Inventorying the national emissions of greenhouse gases is a task shared by several departments within the executive branch of the federal government, including the Environmental Protection Agency, the Department of Energy and the Department of Agriculture. The Greenhouse Gas Inventory chapter summarizes the most current information on U.S. greenhouse gas emission trends--and represents the 1997 submission from the United States in fulfillment of its annual inventory reporting obligation. The estimates presented in this chapter were compiled using methods consistent with those recommended by the IPCC Guidelines for National Greenhouse Gas Inventories; therefore, the U.S. emissions inventory should be comparable to those submitted by others under the FCCC.

Table 1-1 summarizes the recent trends in U.S. greenhouse gas emissions from 1990 to 1995. The three most important anthropogenic greenhouse gases are carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Hydrofluorocarbons (HFCs) are also inventoried. Consistent with the requirements in the Climate Convention only to address emissions of gases not controlled by the Montreal Protocol on Substances That Deplete the Ozone Layer, chlorofluorocarbon (CFC) emissions are not inventoried, nor are mitigation measures for these compounds described.

Overall, U.S. greenhouse gas emissions have increased annually by just over one percent. The trend of U.S. emissions--which decreased from 1990 to 1991, and then increased again in 1992--is a consequence of changes in total energy consumption resulting from the U.S. economic slowdown in the beginning of this decade and its subsequent recovery.

Carbon dioxide accounts for the largest share of U.S. greenhouse gases--approximately 85 percent--although the carbon sinks in forested lands offset CO2 emissions by about 8 percent. During 1990-95, greenhouse gas emissions continued to rise in the United States, with CO2 increasing approximately 6 percent, methane approximately 4 percent, N2O nearly 10 percent, and HFCs approximately 7 percent. Fossil fuel combustion accounts for 99 percent of total U.S. CO2 emissions. (Chapter 3 of this report explains the use of MMTCE in converting emissions of greenhouse gases to carbon equivalents.)

Although methane emissions are lower than CO2 emissions, methane's footprint is large: in a 100-year time span it is considered to be twenty-one times more effective than CO2 at trapping heat in the atmosphere and is responsible for about 10 percent of the warming caused by U.S. emissions. In addition, in the last two centuries alone, methane concentrations in the atmosphere have more than doubled. Emissions of methane are largely generated by landfills, agriculture, oil and natural gas systems, and coal mining, with landfills comprising the single largest source of the gas. In 1995, methane emissions from U.S. landfills were 63.5 MMTCE, equaling approximately 36 percent of total U.S. methane emissions. Agriculture supplied about 30 percent of U.S. methane emissions in that same year.

Nitrous oxide is also emitted in much smaller amounts than carbon dioxide in the United States and is responsible for approximately 2.4 percent of the U.S. share of the greenhouse effect. However, like methane, it is a more powerful heat trap--310 times more powerful than carbon dioxide at trapping heat in the atmosphere over a 100-year period. The main anthropogenic activities producing nitrous oxide are agriculture, fossil fuel combustion, and the production of adipic and nitric acids. Figures from 1995 show the agricultural sector emitting 46 percent of the total (18.4 MMTCE), with fossil fuel combustion generating 31 percent.

Hydrofluorocarbons (HFCs) are among the compounds introduced to replace ozone-depleting substances, which are being phased out as a result of the Vienna Convention and its Montreal Protocol on Substances That Deplete the Ozone Layer, and the Clean Air Act Amendments of 1990. Because HFCs have significant potential to alter the Earth's radiative balance, they are included in this inventory. Many of the compounds of this nature are extremely stable and remain in the atmosphere for extended periods of time, which results in a significant atmospheric accumulation over time. U.S. emissions of these gases have risen nearly 60 percent as they are phased in as substitutes for gases that are no longer allowed under the Montreal Protocol--a rate of growth that is not anticipated to continue. Currently, HFCs account for less than 2 percent of U.S. radiative forcing.

Mitigating Climate Change

In October 1993, in response to the threat of global climate change, President Clinton and Vice President Gore announced the Climate Change Action Plan (CCAP). The Plan was designed to reduce U.S. emissions of greenhouse gases, while guiding the U.S. economy toward environmentally sound economic growth into the next century. This report updates the programs in the CCAP (including an appendix providing one-page descriptions of each program), describes several additional initiatives developed to further reduce emission growth rates, and estimates future emissions based on the current set of practices and programs.

CCAP programs represent an effort to stimulate actions that are both profitable for individual private-sector participants as well as beneficial to the environment. Currently, more than forty programs are in effect, combining efforts of the government at the federal, state, and local levels with those of the private sector. The CCAP has five goals: preserving the environment, enhancing sustainable growth environmentally and economically, building partnerships, involving the public, and encouraging international emission reductions.

Carbon dioxide emissions constitute the bulk of U.S. greenhouse gas emissions. CCAP recognizes that investing in energy efficiency is the most cost-effective way to reduce these emissions. The largest proportion of CCAP programs contains measures that reduce carbon dioxide emissions while simultaneously enhancing domestic productivity and competitiveness. Other programs seek to reduce carbon dioxide emissions by investing in renewable-energy and other low-carbon, energy-supply technologies, which will also provide longer-term benefits, such as increased efficiency and related cost-savings and pollution prevention. A smaller number of programs are targeted at methane, nitrous oxide, and other greenhouse gases (Table 1-2).

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