We must take the lead in addressing the challenge of global warming that could make our planet and its climate less hospitable and more hostile to human life. Today, I reaffirm my personal and announce our nation's commitment to reducing our emissions of greenhouse gases to their 1990 levels by the year 2000. I am instructing my administration to produce a cost-effective plan that can continue the trend of reduced emissions. This must be a clarion call, not for more bureaucracy or regulation or unnecessary costs, for American ingenuity and creativity, to produce the best and most energy-efficient technology.

President Bill Clinton

The composition of the atmosphere is a primary determinant of global temperature and climate. In turn temperature and climate establish conditions and limitations for life on earth. There was a time, not long ago, when air quality and climate would not have been included in the same chapter. Today, however, evidence strongly suggests that pollutants emitted into the air from anthropogenic (human-made) sources have the potential to change the climate of the planet.

Air Quality

The good news is that, between 1983 and 1992, auto emissions were down because of pollution control; the bad news is that Americans are driving more miles each year. The nation cannot afford to rest on its air quality laurels.

Conditions and Trends

As a world leader in air pollution control, the United States continues to work toward air quality goals using advanced technologies and innovative policies such as market-based regulation. The Clean Air Act Amendments of 1990 called for achieving air quality goals in a more flexible, cost-effective, market-based manner than had been the case in prior years. These amendments, now in early stages of implementation, will have their major impact in the coming years. Meanwhile in some parts of the nation, exceedances of health-based national ambient air quality standards (NAAQS) set by the U.S. Environmental Protection Agency (EPA) continue to pose risks to human health and the environment.

Americans and Their Cars

The technology that has improved the emission rates of new automobiles is contributing to improvements in air quality. For example 1990-model vehicles emit hydrocarbons and carbon monoxide at only one-third the rate of 1975-model vehicles. In the near future, the nation can expect further reductions in emissions as older vehicles are retired and replaced by newer, cleaner ones. Even with these technological improvements, however, the total vehicle emissions could once again increase if vehicle miles of travel continue to rise.

Various trends are contributing to the continued rise in vehicle miles of travel:

. Increase in the number of workers,

. Increase in vehicle ownership,

. Decrease in vehicle occupancy rate,

. Decrease in use of public transportation,

. Longer average trip length,

. Growth in suburb-to-suburb travel, and

. Low per-mile driving costs.

The real cost of gasoline, for example, is now lower than it was in 1950. Efforts to reduce travel in single-occupant vehicles and total vehicle miles of travel face difficult challenges in light of these trends.

NAAQS Pollutants

Over the past decade, air quality levels in the United States have shown continued improvement. The six pollutants for which the EPA sets NAAQS are carbon monoxide, lead, nitrogen dioxide, ozone, particulates, and sulfur dioxide. Levels tracked by monitoring stations document progress in reducing air levels for each pollutant.

Carbon Monoxide

Carbon monoxide (CO) is a colorless, odorless, and poisonous gas produced by the incomplete burning of carbon in fuels. Elevated carbon monoxide levels can enter the human bloodstream and reduce normal delivery of oxygen to organs and tissues. In areas where levels exceed the NAAQS, the health threat is most serious for persons who suffer from cardiovascular disease, particularly those with angina or peripheral vascular disease, although healthy individuals also can be affected. Such exposure is associated with impairment of visual perception, manual dexterity, learning ability, and performance of complex tasks.

Two-thirds of the nationwide emissions of carbon monoxide are from transportation sources, with the largest contribution coming from highway motor vehicles (such as light-duty gas vehicles and motorcycles, light-duty and heavy-duty gas trucks, and diesels). Long-term trends indicate that emissions for all types of highway vehicles nearly tripled from 1940 through 1970. From 1970 to 1980, emissions from highway vehicles increased only 11 percent, largely because the nation implemented the Federal Motor Vehicle Control Program that regulates emissions from new vehicles. This program has resulted in widespread use of catalytic converters on automobiles to reduce carbon monoxide, nitrogen oxides, and volatile organic compound emissions. Another result has been the use of unleaded gasoline for vehicles with these converters. Since 1980 carbon monoxide emissions have decreased 37 percent as a result of pollution control and retirement of older vehicles without converters.

Ambient atmospheric concentrations of carbon monoxide have recorded a general long-term improvement. The 10-year period, 1983-1992, showed a 34-percent improvement, which agrees with the estimated 30-percent reduction in highway vehicle emissions. These reductions, largely attributable to vehicle emission controls, occurred despite a 37-percent increase in vehicle miles of travel in the United States during the reporting period. The environmental and transportation communities are concerned that rising vehicle miles of travel could overtake the emission improvements realized over the last decade.

Despite these improvements the EPA designated 42 areas as nonattainment for carbon monoxide in November 1993. These areas failed to meet the carbon monoxide NAAQS of 9 ppm in an 8-hour period. Based upon the magnitude of carbon monoxide concentrations, 41 areas were classified as moderate, with Los Angeles alone classified as serious.

Air Quality Success Stories

Prior to 1993 the EPA had designated Syracuse, New York, as moderate nonattainment for carbon monoxide; Knoxville, Tennessee, as marginal nonattainment for ozone; and Greensboro, North Carolina, as moderate nonattainment for ozone. The EPA, in 1993, was able to redesignate these areas as attainment.

First the EPA Administrator had to determine that the areas had attained the national ambient air quality standard and that the improvement in air quality was the result of permanent and enforceable reductions in emissions. In addition other NAAQS criteria had to be met. Each area was required to have an approved applicable implementation plan describing the measures used to reduce emissions and achieve attainment and a maintenance plan showing that the ambient air standard would be maintained for at least ten years after redesignation. These plans are designed for a particular area but draw on national guidance concerning applicable controls for certain types of pollution sources.

Syracuse helped achieve attainment with the carbon monoxide standard through a combination of measures including a traffic management plan for major events in the downtown area (such as concerts and athletic events) and institution of a ride-share program. Knoxville applied reasonably available control technology (RACT) to major emission sources in its efforts to attain the ozone standard. Greensboro, in addition to applying RACT for major sources, adopted an inspection/maintenance (I/M) program in two counties in the nonattainment area.

In September 1993 Syracuse became the first area in the nation to be redesignated by the EPA as attainment.

Lead

The major sources of atmospheric lead emissions are lead gasoline additives, nonferrous smelters, and battery plants. Transportation contributes more emissions than any other sector of the U.S. economy. Exposure to lead can occur through multiple pathways, including inhalation of air and ingestion of lead in food, water, soil, or dust. Lead accumulates in the body in blood, bone, and soft tissue. Because it is not readily excreted, lead also affects the kidneys, nervous system, and blood-forming organs. Exposure in adults to lead levels exceeding the NAAQS can cause seizures, mental retardation, and behavioral disorders. Fetuses, infants, and children are most susceptible to lead, which can cause central nervous system damage; however, individuals as well. Studies show that lead may be a factor in high blood pressure and subsequent heart disease in middle-aged white males.

Lead emissions from highway sources decreased sharply from 1970 to 1986 as a result of the Federal Motor Vehicle Control Program. Gasoline consumption increased 16 percent between 1970 and 1975, but because of the reduced lead content of gasoline, lead emissions from highway vehicles actually decreased 24 percent. Since 1984 lead emissions from transportation sources have decreased 96 percent, brought about by increased use of unleaded gasoline in catalyst-equipped cars, which made up 99 percent of the gasoline market in 1993. In 1984, the unleaded share of the gasoline market was about 60 percent. In addition to the use of unleaded gasoline, the decrease can be attributed to the reduced lead content in leaded gasoline, which went from an average of 1.0 gram per gallon to 0.1 grams per gallon in January 1986.

Programs are also in place to control lead emissions from stationary sources. Lead emissions from fuel combustion by industry and lead smelters, which contribute to total lead emissions, have decreased over the past two decades. The reductions reflect utility and industrial lead-emission controls and some plant closures.

Ambient lead concentrations in urban areas, where most lead- monitoring stations are located, decreased 89 percent since 1984. This improvement has been evenly distributed over the entire network of 204 monitoring sites. Over the past decade, ambient lead concentrations at 66 monitoring sites near such industrial sources of lead as smelters and battery plants improved 63 percent. Most areas in the United States meet national air quality standards for lead. Those that do not are industrial areas impacted by point sources of lead. In 1993 these areas were Cleveland, Ohio; Indianapolis, Indiana; Memphis, Tennessee, and parts of Alabama and Mississippi; Omaha, Nebraska, and parts of Iowa; Philadelphia, Pennsylvania, and parts of New Jersey; and St. Louis, Missouri, and parts of Illinois.

Nitrogen Dioxide

Nitrogen dioxide is a yellowish brown, highly reactive gas present in the urban atmosphere. Formed by the oxidation of nitrous oxide, it is emitted when fuels burn at high temperatures. Nitrogen dioxide plays a major role, together with volatile organic compounds, in the atmospheric reactions that produce harmful, ground level ozone. It is also a precursor to acidic deposition and contributes to environmental nitrogen loading that can affect both aquatic and terrestrial ecosystems.

Nitrogen dioxide can irritate the lungs, cause bronchitis and pneumonia, and lower resistance to respiratory infections such as influenza. Continued or frequent exposure to concentrations exceeding the NAAQS can cause pulmonary edema.

The two main sources of nitrogen dioxide are transportation and stationary fuel combustion from electric utilities and industrial boilers. Emissions from all sources have increased since the turn of the century. Since 1984 reductions have occurred in emissions from many sources, although total 1993 emissions were 1 percent higher than 1984 figures. Fuel combustion emissions have remained relatively constant during the last five years. Most decreases in mobile-source emissions occurred in urban areas. The Federal Motor Vehicle Control Program and the New Source Performance Standards recently set by the EPA have helped reduce the growth of nitrogen dioxide emissions from electric utilities and highway sources.

Ambient concentrations of nitrogen dioxide increased significantly during the first two-thirds of the century as a result of increased fuel consumption. Since 1984, however, concentrations have declined by 12 percent. Los Angeles, the only urban area in the past ten years with recorded violations of the annual average nitrogen dioxide standard, in 1992 for the first time had air quality levels that met this standard and continued to improve in 1993.

Ozone

Trospheric (Ground-level) ozone is a major component of smog. While ozone in the upper atmosphere (stratosphere) benefits life by shielding the earth from harmful ultraviolet radiation from the sun, concentrations of ozone at ground level in excess of the NAAQS are a major health and environmental concern. Ozone is not emitted directly into the atmosphere but is formed through complex chemical reactions between precursor emissions of volatile organic compounds and nitrogen oxides in the presence of sunlight. These reactions are stimulated by light intensity and temperature so that peak ozone levels occur typically during the warmer times of the year, especially under dry, stagnant conditions.

The reactivity of ozone causes health problems because it damages lung tissue, reduces lung function, and sensitizes the lungs to other irritants. Ambient levels of ozone not only affect persons with impaired respiratory systems but healthy adults and children as well. Several hours of exposure to ozone in doses that exceed the NAAQS can reduce lung function in normal, healthy people during exercise. This decrease in lung function generally is accompanied by symptoms including chest pain, sneezing, and pulmonary congestion. Ozone also can damage forests and crops.

Transportation and industrial sources emit volatile organic compounds (VOCs) and nitrogen dioxide, which are the precursor chemicals of ozone. Emissions of VOCs from fuel combustion have declined steadily since 1900, with the exception of a recent peak caused by residential wood combustion. Emissions from industrial processes increased from 1900 to 1970, but emission control devices and process changes have helped limit these increases. Decreases in emissions after 1970 are also attributed to the substitution of water-based emulsified asphalt for asphalt liquefied with petroleum distillates.

Emissions from transportation sources increased from 1900 to 1970, first from railroads and later from highway vehicles. By 1970 railroads were contributing only 1 percent of total emissions, while highway emissions had risen to 41 percent. Since then highway emissions from diesel and gasoline-powered vehicles have declined by 50 percent from the 1970 level as a result of the Federal Motor Vehicle Control Program and national limits on fuel volatility. Overall total emissions of VOCs are estimated to have declined by 9 percent since 1984.

Ambient concentrations of ozone improved nationally by 12 percent from 1983 to 1992. The 1993 composite average is higher than the 1992 level, but it is noteworthy that 1992 ozone levels were the lowest of the past ten years. Since 1984 the expected number of exceedances of the ozone NAAQS also has decreased by 60 percent.

Particulates

Air pollutants called particulates include dust, dirt, soot, smoke, and liquid droplets. Particulates are emitted directly into the air by sources such as factories, power plants, cars, construction activity, fires, and natural windblown dust. Particles also form in the atmosphere from the condensation or transformation of emitted gases such as sulfur dioxide and volatile organic compounds.

The major effects on human health from concentrations of particulates that exceed the NAAQS often are associated with sulfur dioxide. They include breathing and respiratory symptoms, aggravation of existing respiratory and cardiovascular disease, alterations in the body's defense systems against foreign materials, damage to lung tissues, carcinogenesis, and premature mortality. Individuals with chronic obstructive pulmonary or cardiovascular disease, influenza, or asthma as well as children and the elderly are most likely to be sensitive to the effects of particulates. Particulate matter also soils and damages building materials and impairs visibility in many parts of the country.

In 1987 the EPA promulgated annual and 24-hour standards for particulate matter, using a new indicator, PM-10, which includes only those particles with aerodynamic diameter smaller than ten micrometers. These smaller particles are more likely to be responsible for adverse health affects because of their ability to reach the lower thoracic region of the respiratory tract. The new standards specify an expected annual arithmetic mean not to exceed 50 micrograms per cubic meter. They also specify that expected 24-hour concentrations greater than 150 micrograms per cubic meter per year may not exceed one occurrence per year.

PM-10 particulates are emitted by point and nonpoint sources:

. Point Sources. These include fuel combustion by electric utilities and industry; industrial processes involving chemicals, metals, and petroleum; and transportation.

. Nonpoint Sources. Among these are fugitive dust from agriculture, construction, mining, quarrying, paved and unpaved roads, and wind erosion.

Over the 9-year period, 1985-1993, total PM-10 emissions from point sources decreased almost 3 percent. PM-10 emissions by highway vehicles and off-highway vehicles decreased by 7 percent between 1985 and 1993, while emissions from a category entitled, Fuel Combustion, decreased 14 percent. Emissions in this category are produced predominantly by residential wood combustion'-the in-home use of fireplaces and woodstoves. Several innovative approaches to controlling residential wood combustion are responsible for the large decrease in this emission category.

Fugitive dust contributes six to eight times more PM-10 particulates than point sources; it is consistently emitted by construction activity and unpaved roads. Among road types, emissions from unpaved roads have remained fairly steady, while emissions from paved roads are estimated to have increased 30 percent since 1985, most likely due to increased vehicle traffic. Emissions from construction sites have decreased an estimated 13 percent since 1985. Mining and quarrying, sources estimated to be a relatively small contributor to total fugitive particulate matter emissions at the national level, can be major factors in local areas.

A minor contributor to the national total, agricultural tilling is a major source of particulates in specific regions of the country, such as the Great Lakes, Upper Midwest, and Pacific Northwest. Over the 9-year period, 1985-1993, fugitive dust emissions showed no significant change in these areas. PM-10 emissions caused by wind erosion are very sensitive to regional soil conditions and year-to-year changes in total precipitation. Accordingly estimated emissions from wind erosion were extremely high for the drought year of 1988.

Measured ambient air PM-10 concentrations decreased by 20 percent between 1988 and 1993. Declines in particulate levels are attributable to the installation of pollution control devices in electric utilities and to reduced activity in some industrial sectors, such as iron and steel.

Sulfur Dioxide

Ambient sulfur dioxide results largely from stationary source coal and oil combustion, steel mills, refineries, pulp and paper mills, and from nonferrous smelters. The largest and most consistent source of these emissions has been coal-burning electric power plants.

Human exposure to concentrations of sulfur dioxide exceeding the NAAQS can affect breathing and aggravate existing respiratory and cardiovascular disease. Sensitive populations include asthmatics, individuals with bronchitis or emphysema, children, and the elderly. Sulfur dioxide is a primary contributor to acidic deposition (acid rain), causing acidification of lakes and streams and damaging trees, crops, historic structures, and statues. In addition sulfur compounds in the air contribute to visibility degradation in large parts of the country, including some national parks. The conversion of sulfur dioxide to sulfate aerosols in the atmosphere could impact global climate change.

Historic emissions of sulfur dioxide from fuel combustion and industrial processes increased steadily from 1900 until 1925 and then decreased during the 1930s primarily because of the Great Depression, only to increase sharply from 1940 to 1970. During the 1970s and early 1980s, emissions decreased by 25 percent as the result of several factors:

. Coal cleaning and lower sulfur coal blending by electric utilities;

. Reduction in coal burning by industrial, commercial, and residential consumers;

. Increased use of emission control devices by industry, especially

sulfuric acid manufacturing plants; and

. Byproduct recovery of sulfuric acid at nonferrous smelters.

Emissions have declined slightly in recent years. Nationally the long-term trend in ambient sulfur dioxide concentration shows a 26-percent reduction over the 10-year period, 1984-1993, although the annual rate of decline has slowed over the last few years. Currently there are 47 areas in the United States do not meet national air quality standards for sulfur dioxide.

Air Quality Population Estimates

Although ambient air quality improvements in the 1984-1993 period are encouraging, population estimates suggest that 59 million people live in counties where pollution levels failed to meet one or more air quality standards in 1993. Such estimates provide a relative measure of the extent of the problem for each pollutant. As an indicator, however, they have limitations. For example, an individual living in a county that violates an air quality standard may not actually be exposed to unhealthy air.

Smog

Urban, ground-level ozone (smog) continued to be the most pervasive air quality problem, with an estimated 44.6 million people living in counties that did not meet the ozone standard. This figure, however, the lowest for the 10-year period, represents a substantial decrease compared to the 112 million people thought to live in areas that did not meet ozone NAAQS in 1988 when hotter, drier meteorological conditions prevailed and contributed to more ozone formation. The decrease is also partly because of new emission control programs.

Pollution Standards Index (PSI)

The EPA developed the Pollution Standards Index (PSI) as an air quality indicator for describing urban air trends. The PSI has found widespread use in the air pollution field for reporting daily air quality to the general public. The index integrates information from many pollutants across an entire monitoring network into a single number that represents the worst daily air quality experienced in an urban area. It is computed for carbon monoxide, nitrogen dioxide, ozone, particulates (PM-10), and sulfur dioxide. The index is based on short-term National Ambient Air Quality Standards (NAAQS), Federal Episode Criteria, and Significant Harm Levels.

Index Range Health Effects Categories

0 to 50 Good

51 to 100 Moderate

101 to 199 Unhealthful

200 to 299 Very Unhealthful

300 and Above Hazardous

The impact of hot dry summers in 1983 and 1988 in the eastern United States can be measured by examining total PSI data along with PSI data for selected metropolitan areas. Pittsburgh is the only city where a significant number of PSI days greater than 100 are caused by pollutants other than carbon monoxide or ozone; the Pittsburgh pollutants are sulfur dioxide and PM-10 particulates.

Sulfur Dioxide/Nitrogen Dioxide

The year 1992 marked the first time since the EPA began making population estimates that the agency recorded no monitoring violations of either sulfur dioxide or nitrogen dioxide NAAQS.

Program Accomplishments

The nation continues to experiment with innovative programs to reduce motor vehicle emissions that cause smog and industrial emissions that release air toxics and cause acid rain.

Motor Vehicle Emissions

Cleaner fuels and cleaner engines, sophisticated emissions testing, and rethinking of intermodal transportation systems can help increasingly mobile Americans clean up unhealthy air.

Cleaner Fuels

National limits on gasoline volatility-its tendency to evaporate-already have contributed to lower ozone levels, as observed during the summers of 1991 and 1992. Oxygenated fuel was introduced during the winter of 1992-1993, becoming the first major fuel measure authorized by the Clean Air Act Amendments of 1990 to take effect. Increasing the oxygen content of gasoline reduces carbon monoxide emissions by improving fuel combustion, especially in colder temperatures where fuel combustion is less efficient at the beginning of the driving cycle. As a result, oxygenated fuels contributed to a reduction in exceedances of the carbon monoxide standard in the 35 cities implementing the program. Some motorists have complained that pumping the new fuel at self-service pumps caused dizziness or headaches. EPA studies into these effects concluded that substantial risk of acute health symptoms among healthy members of the public receiving typical environmental exposure is unlikely. Although chronic developmental, cancer, and non-cancer effects from oxygenated gasoline cannot be precisely quantified, they are likely to be no more serious than effects from non-oxygenated gasoline. Nonetheless, the EPA has provided waivers in some very cold areas (such as Alaska) while assessing other solutions to reduce emissions.

New Quality Standards. In 1993 new quality standards took effect, limiting the sulfur content of diesel fuel. The limits will reduce particulate emissions from in-use diesel engines and pave the way for particulate-control technology in new diesel engines. The existing technology is not as effective with high-sulfur fuel.

Cleaner Fuel Regulations. In December 1993 the EPA finalized regulations that call for a new generation of cleaner, reformulated gasolines to reduce hydrocarbon and toxic emissions by at least 15 percent by 1995 and by over 20 percent by 2000 in the nine cities most polluted with ozone.

Cleaner Cars, Trucks, and Buses

Tighter emission standards requiring exhaust hydrocarbon emission reductions of 30 percent and nitrogen oxide emission reductions of 60 percent from new cars and light trucks will be phased in beginning with the 1994 model year. In March 1993 the EPA also finalized rules requiring a 90-percent reduction in particulate emissions from new urban buses by 1996.

Inspection and Maintenance

Enhanced vehicle inspection and maintenance (I/M) may make the largest contribution toward improved urban air quality of any measure in the Clean Air Act. The 1990 Clean Air Act has resulted in the implementation of stricter vehicle tailpipe and evaporative emission controls that increasingly will benefit all areas over the next two decades. Enhanced I/M uses high technology testing on an annual or biennial basis along with supplemental on-road emissions testing to ensure that vehicles meet these standards. Maintenance is required to bring nonconforming vehicles into compliance. The EPA estimates that enhanced I/M, now required in approximately 100 urban areas, can yield a 28-percent emissions reduction. During 1993 the states took the first steps toward implementing the enhanced I/M program, which will be phased in during 1995.

Transportation

While emissions from new vehicles on a per-mile basis are a fraction of the levels of 20 years ago, the number of miles driven has doubled over that period and continues to rise. The Clean Air Act of 1990 and the Intermodal Surface Transportation Efficiency Act of 1991 together require states and local areas to rethink traditional approaches toward planning and providing transportation services. In 1993 the EPA finalized a transportation conformity rule requiring that transportation and air-quality planning be conducted in concert to maintain air-quality goals. The EPA and Department of Transportation (DOT) worked together to develop innovative transportation strategies outlined in a 1993 report, Clean Air Through Transportation: Challenges in Meeting National Air Quality Standards. These strategies provide guidance and technical assistance to state and local governments in reconciling environmental and mobility goals.

Fleet Vehicles

Beginning in 1998 in 22 cities, the EPA will require new fleet vehicles, such as taxis and delivery vans, to meet tailpipe standards more stringent than those required for conventional vehicles. New EPA guidelines provide incentives for fleet owners to purchase Inherently Low-Emitting Vehicles (ILEV) fueled with natural gas, propane, pure alcohol, or electricity (see Chapter 7).

Air Toxics

Toxic pollutants -those known or suspected to cause cancer or other serious health effects- are released into the air in many areas of the United States. Two EPA programs serve as primary sources of information on air toxics:

. Toxics Release Inventory. The TRI covers air toxics emissions, and

. National Volatile Organic Compound Database. The database, in conjunction with field studies, covers air toxics concentrations.

According to estimates of those industries participating in the TRI, more than 2 billion pounds of toxic pollutants were emitted into the air in 1991. This is a reduction from 1990, when 2.2 billion pounds were emitted. Among the top-ten air toxics in terms of quantities reported, TRI emissions showed a downward trend for all but one of the pollutants listed. The EPA projects that, with implementation of the Clean Air Act Amendments, this downward trend will continue.

The EPA is implementing a comprehensive program to reduce routine emissions of hazardous air pollutants to doses below their known or suspected levels of causing cancer or other serious health effects such as birth defects. The Clean Air Act Amendments of 1990 require the EPA to establish standards over a 10-year period to regulate emissions of 189 chemicals listed in the legislation. In 1993 the EPA took steps to reduce emissions of hazardous air pollutants in the following industries:

Dry Cleaners. In September 1993 the EPA issued a final rule requiring technology controls and/or improved work practices for 25,000 industrial and large commercial dry cleaners. These popular businesses are a major source of perchloroethylene, one of the air toxics that Congress listed for control in the Clean Air Act. The rule is expected to result in a national reduction of as much as 35,600 tons per year of perchloroethylene emissions.

Coke Ovens. In October 1993 the EPA issued a final rule sharply reducing emissions from coke oven batteries. Coke is used in blast furnaces for the conversion of iron ore to iron in the process of making steel; the conversion is performed in coke oven batteries. Coke oven emissions are among the most toxic of all air pollutants, with preregulation maximum individual risks of contracting cancer running as high as 1 in 100 in some cases. The EPA developed the final rule through a formal regulatory negotiation that included representatives from the steel industry, state and local agencies, environmental groups, and the Steel Workers Union. The rule will result in overall reductions of 82 to 94 percent of total emissions from coke ovens.

Industrial Cooling Towers. In August 1993 the EPA issued a proposed rule to eliminate emissions of chromium, a highly toxic chemical, from industrial process cooling towers. The proposed rule requires substitution of nonchromium-based chemicals for chromium. The result will be a 100-percent reduction in chromium emissions from these cooling towers.

Halogenated Solvent Cleaners. In November 1993 the EPA issued a proposed rule to reduce emissions from solvent cleaning machines of halogenated solvents including methylene chloride, perchloroethylene, trichloroethylene, 1,1,1-trichloroethane, carbon tetrachloride, and chloroform. Major industries using halogenated solvents include the aerospace industry, motor vehicle manufacturing facilities, the fabricated metal products industry, and the electric and electronic equipment industry. The proposed rule, a combination of equipment standards with work practices, will result in a reduction of hazardous air pollutant emissions of 88,400 tons per year.

Chromium Electroplating and Anodizing Operations. In November 1993 the EPA issued a proposed rule that will require the application of maximum achievable control technology for about 5,000 chromium electroplating and anodizing operations. These operations are a major emission source of highly toxic chromium compounds listed for control in the Clean Air Act. The rule is expected to result in a national reduction of as much as 173 tons per year of chromium emissions.

Indoor Air Quality

During the past 20 years, as outdoor air pollution decreased, indoor air pollution increased because of the following factors:

. Construction of more tightly sealed buildings,

. Reduction of ventilation to save energy,

. Use of synthetic building materials and furnishings, and

. Use of chemically formulated personal care products, pesticides,

and household cleaners.

Indoor air pollutants include tobacco smoke, radon, volatile organic compounds, biological contaminants, combustion gases, respirable particulates, lead, formaldehyde, and asbestos. Diseases such as asthma, chronic bronchitis, emphysema, and lung cancer-all of which have increased in the United States over the past two decades-have been linked to these indoor air pollutants. While a difference exists in sensitivity from person to person, the following indoor air pollutants are areas of special concern:

Secondhand Smoke

Environmental tobacco smoke (ETS), often called secondhand smoke or passive smoke, is a major concern. In a December 1992 report, Respiratory Health Effects of Passive Smoking: Lung Cancer and Other Disorders, the EPA estimated that ETS causes over 3,000 lung cancer deaths a year among nonsmokers and may be responsible for serious respiratory illness in hundreds of thousands of children. As public awareness of the hazards of ETS exposure increases, businesses and communities across the nation are taking actions to prevent involuntary exposure through prohibiting smoking indoors or limiting smoking to specially designated, separately ventilated smoking rooms. In July 1993 the EPA released a brochure, -What You Can Do About Secondhand Smoke,- which summarized preventive actions.

Radon

Studies by the National Academy of Science estimate that the naturally occurring gas, radon, is the cause of 7,000 to 30,000 lung cancer deaths nationwide each year. Most of these deaths occur among people who smoke cigarettes. The 1992 Radon Risk Communication and Results Study, conducted by the State Conference of Radiation Control Program Directors and sponsored by the EPA, found that 67 percent of Americans show some awareness that radon is a potential concern; 9 million U.S. homes have been tested for radon; and 300,000 of the 6 million homes estimated to have radon problems have been treated to mitigate the gas. The study, which yielded statistics for each state and for target areas within each state, found greater action to address radon in states with higher radon potential. Public and private sectors are using the study to establish a baseline for tracking and improving bottomline environmental results.

Sick-Building Syndrome

Initially reports of mild symptoms in people working in sealed, usually recently constructed, office buildings were discounted. Now scientific experts are reaching agreement that degassing of certain building materials can cause significant health effects. The following reasons have led to this conclusion:

Similarity of Symptoms. A remarkable concordance exists among the kinds of complaints made by workers in different locations and in different countries. Complaints include headaches, fatigue, inability to concentrate, and mild inflammation of the eyes and pharynx. Diary data comparing complaints of symptoms that arise from working in new office buildings show a remarkable similarity.

Identification of Volatile Organic Compounds. Among the volatile organic compounds identified as commonly present in buildings where complaints of symptoms occur are formaldehyde, toluene, and trichloroethylene. Controlled-exposure studies of these compounds, such as a recent Danish study of n-decane exposure, find them to be common in building materials.

Asthma and Other Respiratory Problems

During the past several decades, knowledge of factors related to asthma and other respiratory problems has expanded greatly. Exposures to a wide range of substances-more than 200 have been implicated-can induce airway responsiveness. In addition to outdoor exposure to ozone and sulfur dioxide, these include indoor exposure to environmental tobacco smoke, toluene, anhydrides, platinum salts, and some acids and aerosols. Recent data have demonstrated a correlation between summer pollutant levels and respiratory morbidity as indicated by hospitalization admissions. Hospital admissions for asthma have been increasing, along with increases in asthma mortality. While hospital admissions for asthma declined for the total population in 1992, they continued to increase for blacks and other nonwhites and for children.

Indoor Air Management

A total of 20 federal agencies have responsibilities associated with indoor air quality, either through statutory mandates or as major property managers.

Committee on Indoor Air Quality. In 1993 the interagency Committee on Indoor Air Quality (CIAQ), with members from the EPA, Consumer Product Safety Commission, Department of Energy, Department of Health and Human Services, and Occupational Safety and Health Administration, coordinated control efforts.

Legislative Authority. The federal government administers indoor air programs under the authority contained in statutes such as Title IV of the Superfund Amendments and Reauthorization Act (SARA), which requires the EPA to conduct research and disseminate information on the subject. The Federal Insecticide Fungicide and Rodenticide Act (FIFRA) and the Toxic Substances Control Act (TSCA) authorize the EPA to regulate products that adversely affect indoor air quality.

EPA Radon Program

To reduce the significant health threat of radon, the EPA radon program has set the following priorities as recommended by a panel of senior EPA officials and radon experts from outside the agency:

. Target high risk geographic areas and populations that include smokers;

. Promote radon-resistant new construction techniques;

. Encourage radon testing and mitigation as part of real estate transfers;

. Sustain a national public education campaign; and

. Develop a coordinated research plan with other federal agencies.

Acid Rain and the Clean Air Act

During the last several decades, strong acids (sulfuric and nitric acids), formed when atmospheric pollutants emitted from power plants, factories, and motor vehicles combine with water in the atmosphere, have fallen as acid rain and snow on the northeastern United States and southeastern Canada. This acidic precipitation is believed to be responsible for the acidification of sensitive lakes and streams, damage to historical structures and high-elevation forests, and impaired visibility in affected areas. The following are among the technical problems that have been recognized:

. Some watersheds in regions receiving high nitrogen deposition (such as the Adirondacks and Catskills) and some old-growth forests in the Appalachians are becoming nitrogen saturated. In many cases nitrogen inputs are exceeding the capacity of the watersheds to retain nitrogen and are contributing to increased leaching of soil nutrients and/or surface water acidification.

. Declines in northeastern high-elevation red spruce forests are associated with ambient concentrations of pollutants in cloud water and rain which reduce the midwinter cold tolerance by 4 to 10 degrees Celsius compared with trees growing at the same locations but at lower elevations.

. Chemical changes in forest ecosystems and surface waters attributable to acidic deposition are reported in some national parks.

. Wet and dry acidic deposition accounts for an estimated 31 to 78 percent of the dissolution of galvanized steel and copper in outdoor exposures.

National Trends Network

The U.S. Geological Survey coordinates the operation of the National Trends Network (NTN), a 150-station, nationwide multiagency network for monitoring precipitation chemistry in the United States. In addition NTN monitors selected sensitive lakes and streams throughout the nation to document changes in water chemistry that may result from the effects of acid rain. The Network also conducts research in several sensitive watersheds to define how geochemical processes caused by acid rain affect water quality. NTN data reveal substantial differences in precipitation chemistry between the eastern and western regions of the United States. As an example, for the period 1985 through 1993, the following conclusions have been reached:

. Sulfate concentrations are two to three times higher in the East than in the West, and an apparent decreasing trend for sulfate concentrations in the East is not evident in the West;

. Nitrate concentrations are consistently higher in the East, despite the lack of an obvious temporal pattern over the summary period;

. Ammonium concentrations, uniform across much of the United States, do not exhibit any temporal pattern;

. Calcium concentrations in precipitation are higher in the West, although the difference is less than 0.01 milligrams per liter between regions;

. The combination of higher concentrations of acid anions (sulfate and nitrate) in the East and similar to somewhat higher concentrations of cations (ammonium and calcium) in the West results in a consistently lower pH (higher hydrogen ion concentration) in the East; and

. Although the pH levels are less than one pH unit lower in the East, the amount of hydrogen in precipitation is five to six times greater than in the West.

Regional differences evident in concentration data for precipitation chemistry are even more evident in concentration data for wet deposition; however, temporal patterns are not as evident. Regional differences in the amount of precipitation (for instance, the East has considerably more precipitation than the West but less year-to-year variability) and concentrations of ions help to explain the following spatial trends in ionic deposition:

. Wet sulfate and nitrate deposition tends to be four to five times greater in the East than in the West;

. Ammonium deposition is generally twice as high in the East;

. Calcium deposition is only slightly higher in the East caused by the offsetting influence of lower concentrations in precipitation; and

. The average annual difference in the amount of wet hydrogen deposition in the East relative to the West is eight-fold.

While acidic deposition continues to effect sensitive forest, soil, and aquatic ecosystems, the effect of recent, relatively small reductions in the emissions of sulfur dioxide and nitrogen oxides are difficult to detect.

Acid Rain Program

The EPA administers the Acid Rain Program, which is designed to achieve significant environmental benefits through reductions in emissions of sulfur dioxide and nitrogen oxides. To achieve this goal at the lowest cost, the program employs both traditional and innovative, market-based approaches for controlling emissions. It is designed to encourage both energy efficiency and pollution prevention. Efforts were underway in 1993 to evaluate the costs, benefits, and effectiveness of the Acid Rain Program as part of the requirement to assess the costs and benefits of the entire Clean Air Act. The Acid Deposition Standard Study under section 404 (Appendix B) of the Act will provide insight into the environmental effectiveness of the Acid Rain Program.

Rules and Guidance. The EPA implements the Acid Rain Program through an integrated set of rules and guidance:

. Core Acid Rain Final Rules. The agency promulgated these rules in January 1993 (see Continuous Emissions Monitoring below);

. Final Allowance Allocation Rules. The EPA promulgated these rules in March 1993 (Emission Allowance System below);

. NOx Rule. The Acid Rain Program proposed the NOx Rule for a nitrogen oxides emission reduction program in November 1992; the Clean Air Act calls for a 2-million-ton reduction in NOx emissions by the year 2000;

. Opt-In Rule. This rule allows sulfur dioxide emitting sources other than electric utilities to participate in the Acid Rain Program, providing the opportunity for further low-cost reductions of sulfur dioxide emissions; the final Opt-In rule for combustion sources was published in the Federal Register on September 24, 1993.

Continuous Emission Monitoring (CEMs). Implementation of the acid rain core rules was underway in 1993. All 110 sources subject to Phase I of the sulfur dioxide emissions reduction program have submitted permit applications; draft permits were issued in August 1993, and one-third of the final permits were issued in 1993. The EPA has reviewed over 100 Phase I Continuous Emission Monitoring (CEM) plans, and affected utilities have installed and tested 900 CEMS. Emissions data for Phase I sources were submitted to EPA in January 1994.

Emission Allowance System. To achieve a 10 million_ton reduction in sulfur dioxide emissions, the Acid Rain Program administers an emission allowance system, by which the EPA allocates emission allowances to electric utilities in designated amounts that reflect an overall cut in emissions. To achieve these reductions, the law requires a 2_phase reduction in emissions from fossil fuel_fired power plants. A nationwide cap of 8.95 million tons of sulfur dioxide will be maintained with individual units deciding their own plan for compliance, as long as they stay within their allowance limit. A utility can cut its emissions more than required and sell its extra allowances to another utility or bank them for future use. At the end of each year, utilities must hold enough allowances to cover their emissions. Noncompliance earns automatic penalties.

Emission Allowance Trades and Auctions.

Emisson Allowance Trades and Auctions. A limited number of two-party and brokered trades are occurring in the allowance market, with announced prices ranging from $250 to $350 per allowance. On March 29, 1993, the EPA held an auction conducted by the Chicago Board of Trade, which has been delegated the administrative functions of the allowance auction. About 150,000 allowances were sold with selling prices ranging from $122 to $450 per allowance. Private auctions are expected to occur when the EPA allowance tracking system becomes operational in 1994.

Conservation Verification Protocols. In March 1993 the EPA published Conservation Verification Protocols to provide guidance on energy conservation to the regulated community. The system, in which each ton of sulfur dioxide a utility avoids emitting means one fewer allowance retired and one more that can be sold at a profit, creates an inherent incentive for utility energy conservation.

National Acid Precipitation Assessment Program

The National Acid Precipitation Assessment Program (NAPAP) was reauthorized under Title IX of the 1990 Clean Air Act Amendments (CAAA) to monitor and assess the effects of the Acid Rain Program (Title IV, CAAA). NAPAP coordinates the federal acidic deposition research and monitoring program in addition to its new charges of evaluating the costs of Title IV and determining the reduction in deposition rates needed to prevent adverse ecological effects. As required by the CAAA, NAPAP reports to Congress on its investigations, analysis, and assessments. The first of these reports, which was issued in 1993, summarizes the evolution of public policy, regulatory, and technical environments within which NAPAP is operating and updates the results of relevant scientific investigations and analysis. Evaluation of costs and benefits will be addressed by NAPAP under section 901 of the Clean Air Act, with reports issued every four years beginning in 1996.

Climate

Global climate change and the effect of greenhouse gases on it were the major climate issues of the year, along with temperature and precipitation extremes in the United States which varied from ice storms to heat waves and from droughts to disastrous floods.

Conditions and Trends

Climate, the average weather in an area over a long period of time, can be described in terms of temperature, precipitation, humidity, sunshine, atmospheric pressure, and wind conditions that prevail at different times of the day or year. Other factors include extremes in range, variability, and frequency of variation.

Major U.S. Weather Events

Checking the long_term record, the contiguous United States experienced lower than average temperature but higher than average precipitation during 1993.

Record Temperature Extremes

The year 1993 started out with moderate average monthly temperatures for most of the country, but, as the year progressed, large areas experienced temperatures of both extremes. By July 1993 a sixth of the country was reporting very warm conditions, while at the same time about a third of the contiguous United States was experiencing very cold conditions. The -very warm- category is defined statistically as that monthly average temperature (or warmer) occurring less than 10 percent of the time throughout the 99-year U.S. climate data record; -very cold- is similarly defined for the cold end of the scale.

Statewide temperature ranks for May-August 1993 showed very warm anomalies along the east coast and very cold anomalies in the northwestern quarter of the country. Seven states ranked among the warmest on record while four states ranked among the coldest.

Unusually cold temperatures occurred for at least a tenth of the country through mid-summer to late fall (July-November), with over a fourth of September readings and nearly a third in November unusually cold. The cold anomalies were located largely from the Central Plains to the Pacific Northwest. In 1993 despite extreme spring and summer temperatures in the Southeast, the contiguous United States as a whole had the 13th coldest year on record.

Record Precipitation Extremes

Parts of the United States experienced excessive precipitation during 1993, but other parts were exceptionally dry. The year started out wet, with more than a fourth of the country experiencing very wet conditions in January, and a sixth of the country reporting very wet conditions in February. The -very wet- category is defined statistically as that amount of precipitation (or greater) occurring less than 10 percent of the time throughout the 99-year U.S. climatic data record; -very dry- is similarly defined for the dry end of the scale. Both very wet and very dry conditions occurred during the summer months: more than a fifth of the country was very wet in June and more than a fourth was very wet in July, while over a fourth was excessively dry during July and a seventh during September.

The period May-August 1993 was characterized by extreme precipitation anomalies. Excessive rains occurred from the Northwest to the Midwest, while severe dryness occurred along the east coast. Using statewide precipitation ranks based on 1895-1993 data, the May-August 1993 period showed 14 states with among the wettest periods on record; Iowa, Montana, and North Dakota ranked as the wettest on record. Thirteen states had among the driest May-August periods on record, with North Carolina ranking as the driest. In 1993 the contiguous United States as a whole had the 13th wettest year on record.

Record flooding occurred along parts of the Mississippi River during the summer of 1993, causing record property and crop damage and closing the river to ship and barge traffic (see Chapter 2: Water Quantity and Quality). Based on 99-year data, the upper Mississippi River basin in 1993 had the wettest April-August period ever. Ironically only five years ago, ship and barge traffic was halted due to near-record dryness reminiscent of the persistent drought of the 1930s.

Much of the primary corn and soybean agricultural region is located within the Mississippi River basin. In 1993 this agricultural belt had the wettest June-September on record; this period encompasses much of the growing/harvesting season.

The Southeast region of the United States in 1993 had the driest May-August period in the 99-year record. Severe crop losses occurred in South Carolina and parts of North Carolina and Georgia because of the drought.

The dryness of summer 1993 rapidly increased the percentage of the South Atlantic-Gulf Coast drainage basins with severe to extreme drought, reaching about 10 percent of the region by August 1993, with another 50 percent of the region in the moderate drought category. The severe drought area persisted at about the 10-percent level through the end of 1993. This occurred after a 2-year respite from severe drought in the region.

In August 1993 about 43 percent of the contiguous United States suffered under severely to extremely wet conditions. By this measure, only four other wet episodes in this century (1915, 1941, 1973, and 1983) have been as severe.

Hurricanes

Only 15 percent of current U.S. coastal residents have experienced a major hurricane, but with the population in storm-vulnerable coastal counties growing rapidly, increasing numbers of people are being exposed to such risks. New residents are the least experienced with hurricanes, but because of a long absence of disastrous hurricanes along most of the coast, even longtime residents have little hurricane experience.

The total amount of real property exposed to the risk of hurricanes is staggering. Hurricane Andrew in 1992 caused estimated direct losses of $26 billion, with indirect losses to businesses of another $15 billion; yet it could have been much worse. Had Andrew struck a mere 20 miles farther north in the financial/business center of Miami, the direct damage could have been $70 billion, with even higher indirect business losses. Andrew sent shock waves through the U.S. economy when several insurance companies failed and later when wind insurance premiums increased tenfold. Each decade holds the potential for several hurricanes like Andrew or worse.

Hurricane Preparedness

During the first 90 years of this century, the United States suffered direct hits by 60 major hurricanes, an average of two out of every three years. Each of these storms now has the potential to be a multibillion-dollar event. The risk of larger hurricane disasters, in terms of loss of life and damage, is increasing. Coastal communities need to address hurricane preparedness on every possible front.

Forecast Uncertainty. The nation still faces uncertain hurricane forecasts. Increased precision in forecasting the point of impact and the strength of the hurricane could limit the population to be evacuated to a level that existing roads could handle. The simple provision of longer lead times and more targeted warnings would allow the repositioning of rolling stock-buses, trucks, recreational vehicles, airplanes, trains, and even boats-thus removing this expensive property from harm's way.

Overdevelopment. A second problem results from the overdevelopment of coastlines. More realistic land-use policies would minimize the growth of the population at risk. The nation needs policy changes to modify or eliminate federal programs that subsidize or otherwise encourage development in the vulnerable coastal zone. Communities need local planning to provide limited, targeted evacuation and last-resort refuges for those who do not evacuate in time.

Unnecessary Preparations. Improved hurricane forecasting and response offers a potential payoff by reducing unnecessary preparations. Such reductions, which could save millions of dollars, depend ultimately on more precise and targeted hurricane warnings.

Lax Building Codes. The potential savings from well-timed preparations in areas hit by a hurricane are even more impressive than savings from the reduction of unnecessary preparations. A good building code was in effect for Andrew in Dade County, Florida, but compliance was deficient. Good code enforcement and inexpensive hurricane shutters could have reduced damages by several percentage points. Such savings would have been significant, considering that 1 percent of the Andrew damage equalled $260 million. Building codes are not as good for the rest of the nation's coastal areas, and thus strict enforcement of better codes represents an area where hurricane preparedness can have a substantial impact.

A major hurricane has yet to hit a large coastal city in modern times, but with the concentration of population along the coast, such an event is inevitable. City infrastructures, including roads and bridges, have not kept pace with population increases, leaving in question the ability of cities to quickly evacuate large populations along the Atlantic and Gulf of Mexico coastlines. Despite increased emergency planning, the record of decreasing hurricane fatalities in this century could be in jeopardy.

Tornadoes

In 1993 the United States experienced 1,173 tornadoes across the country, above the long-term 30-year average of 863 but lower than the 1992 record of 1,297. State-by-state distribution shows that the majority of these storms occurred in tornado alley-that area of the central United States and Gulf coastal plain with a historically high annual probability of tornado occurrence. In 1993 several states reported record numbers of tornadoes:

State Number of Tornadoes

South Dakota 85

Minnesota 47

Virginia 28

Idaho 11

Utah 6

The 1993 death toll was below normal at 33 compared to the average of 82. In the decade ending in 1980, the tornado death toll in the United States was 953. For the 10-year period ending in 1993, that figure had decreased to 536. Several factors have contributed to this trend:

National Severe Storms Forecast Center. The NSSFC is responsible for monitoring current and projected weather patterns to alert the public of the potential for severe weather episodes. The success of this program is measured in the decline in deaths.

National Weather Service Warning Program. Improvements in the NWS warning program have allowed it to reach more citizens, helping them to take precautions for tornadoes.

Local Weather Service Offices. Preparedness efforts sponsored by local weather service offices have raised public awareness of the threat.

Emergency Managers and Volunteers. Safety and preparedness efforts by emergency managers, volunteer spotters, and ham radio operators also have produced a more enlightened public.

The frequency of tornadoes in the United States would seem to indicate a sharp increase in tornado activity in recent years. A detailed examination of the data, however, shows that this is not the case. The explanation is better detection. U.S. tornadoes dating back to 1953, if categorized by intensity-the weak ones versus the strong or violent ones-show a dominance of weak tornadoes. These account for most of the variability and rise in tornado totals that culminated in the record or near record totals for the past four years. One of the factors that has caused this phenomenon is a greater emphasis on report gathering and warning validation by the NWS. Increased populations, storm chasing, and the advent of the video camera have also contributed to the detection of weaker tornados that previously might have been missed. Since the numbers of strong and violent tornadoes have not undergone the growth exhibited by weak tornadoes, it is likely that significant tornadoes represent the true tornado climatology.

Global Environmental Change

While human activities have long influenced local environments, only since the start of the Industrial Revolution and subsequent rapid population growth have human activities begun to have a significant influence on the global environment. These activities are inducing changes in the earth system which may have major environmental consequences: long-term climate change and greenhouse warming, stratospheric ozone depletion and increased ultraviolet (UV) radiation, changes in natural seasonal to interannual climate variability, and large-scale changes in land cover and terrestrial and marine ecosystem productivity. Understanding the causes and implications of large-scale global environmental change is instrumental in determining what courses and actions must be considered now and in the future to ensure the compatibility of economic growth, protection of the global environment, and long-term sustainability of the quality of life.

Greenhouse Gases

Trace gases in the atmosphere comprise only about 1 percent of its composition but provide two vital functions: they warm the earth's surface by trapping infrared (heat) energy in the atmosphere; and they shield the planet from harmful radiation. These gases are referred to as greenhouse gases. Their warming capacity, called the greenhouse effect, is essential to maintaining a climate hospitable to all life forms.

Greenhouse gases regulate the global climate by stabilizing the balance between the earth's absorption of heat from the sun and its capacity to reradiate heat back into space. Activities that can change this balance include natural, such as changes in solar radiation and volcanic eruptions, and human-induced, arising from industrial and land-use practices that release or remove heat-trapping greenhouse gases, thus changing atmospheric concentration. Greenhouse gases include water vapor, carbon dioxide, methane, nitrous oxide, chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and ozone in the lower stratosphere and troposphere. While water vapor has the largest effect, its concentrations are not directly affected, on a global scale, by human activities. Most of these gases occur naturally, the exceptions being CFCs, HCFCs, HFCs, and PFCs, but human activities'combustion of fossil fuels, deforestation, rice cultivation, mining, and the use of nitrogen fertilizers, refrigerants, and solvents'have contributed to increases in their atmospheric concentrations. Internationally accepted science indicates that increasing concentrations of greenhouse gases ultimately will raise atmospheric and oceanic temperatures and could alter associated circulation and weather patterns. Many greenhouse gases have long atmospheric residence times- several decades to centuries-which implies that the atmosphere will recover very slowly, if at all.

Since 1990 U.S. emissions of carbon dioxide have increased while emissions of other greenhouse and photochemically important gases have remained constant or have declined. A summary of trends for the main greenhouse gases follows.

Carbon Dioxide. Large natural sources and sinks of carbon dioxide function in a balanced cycle, with human activities accounting for a smaller, but increasingly important source of emissions. Global atmospheric concentrations of carbon dioxide have increased about 30 percent since the 1700s, suggesting that the natural carbon cycle may be out of balance. This increase is responsible for more than half of the global -heat trapping- or -radiative forcing- due to human activities.

Since the 1950s observations of carbon dioxide have shown regular annual increases in both concentration and rate of concentration growth, with year-to-year variations in growth rate. During the period 1991 to 1993, the rate of increase of carbon dioxide per year slowed, substantially and inexplicably, to as low as 0.5 parts per million by volume (ppmv) per year from as high as 1.5 ppmv per year. Numerous examples exist of short periods where growth rates are higher or lower than the long-term mean. The most recent observations indicate that growth rates of carbon dioxide are increasing again.

The main anthropogenic sources of carbon dioxide are the burning of fossil fuels (with additional contributions from cement production) and land-use changes. In the United States, anthropogenic emissions are divided fairly evenly among sectors. Fossil-fuel combustion produces 99 percent of the total gross U.S. emissions. The industrial sector is the largest source of fossil-fuel carbon dioxide emissions while the transportation sector, second to industry in quantity, had the fastest growth rate in emissions during the last decade. Cement production involving the calcination of limestone, lime production, steel making, and industrial carbon dioxide production account for the remaining 1 percent of total emissions. Absorption of carbon dioxide in U.S. forests (carbon -sinks-) has increased in recent years.

The United States is the world's largest source of energy-related carbon dioxide emissions, followed by the former Soviet Union and China, India, and Germany. In 1950 U.S. fossil-fuel carbon dioxide emissions accounted for more than 40 percent of global emissions; since then, however, this share has steadily declined to 22 percent. Emissions in the developing world, while a relatively small portion of the total, continue to rise rapidly, particularly in the Far East.

Methane is a potent greenhouse gas. Considering only its heat-absorption potential, one molecule of methane has 20 times more effect on climate than one molecule of carbon dioxide. Global concentrations of methane in the atmosphere have more than doubled over the last two centuries and since 1983 have increased by 7 percent, even though the globally averaged methane growth rate declined. Recent data suggest that the growth rates started to increase in late 1993.

Scientists have concluded that atmospheric increases in methane are largely caused by increasing emissions from anthropogenic sources, such as landfills, agricultural activities, fossil fuel combustion, coal mining, the production and processing of natural gas and oil, and wastewater treatment. Landfills are the largest source of methane emission in the United States-they represent a third of U.S. methane emissions-followed by emissions from agriculture (primarily cattle production) and emissions from oil, gas, and coal production collectively.

Methane is also produced naturally via anaerobic decomposition. Wetlands provide the largest natural source, followed by termites. While termites are only a trivial natural methane source in temperate zones, they are ubiquitous in the tropics and when tropical forests are logged or burned, vast quantities of wood residue provide ideal conditions for termite population explosions.

Nitrous Oxide. Nitrous oxide, commonly known as laughing gas, is a potent, stable greenhouse gas with a long atmospheric lifetime, from 120 to 150 years. Although actual emissions of nitrous oxide are smaller than those of carbon dioxide, nitrous oxide is approximately 270 times more powerful than carbon dioxide at trapping heat in the atmosphere over a 100-year time horizon.

The many small sources of nitrous oxide, both natural and anthropogenic, are difficult to quantify. A best estimate of the current (1980s) anthropogenic emission of nitrous oxide is 3 million to 8 million metric tons per year. Natural sources are probably twice as large. Atmospheric concentrations of nitrous oxide have increased by 8 percent over the last century, which is most likely due to human activities. The average growth rate over the past four decades is about 0.25 percent per year (0.8 parts per billion per year).

The primary source of nitrous oxide emissions in the United States is agricultural fertilizer use and soil management. Lesser sources include fossil fuel combustion by mobile and stationary sources, adipic acid production, nitric acid productions, and burning of agricultural crop residues.

Halocarbons. Halocarbons containing fluorine, chlorine, and bromine are significant greenhouse gases on a per molecule basis. Direct radiative forcing (heat trapping) due to increases in halocarbons since pre-industrial times represents about 12 percent of the greenhouse gas contribution. Chlorine from chlorofluorocarbons (CFCs), carbon tetrachloride, and methyl chloroform and bromine from halons are also linked to stratospheric ozone depletion to varying degrees. CFCs have been long and widely used as refrigerants, foaming agents, solvents, and aerosol propellants. Carbon tetrachloride and methyl chloroform are industrial solvents, and halons are used in fire suppressors. Emissions of many such ozone-depleting compounds are controlled by the Montreal Protocol and its subsequent amendments and adjustments:

. The Montreal Protocol. The 1987 Montreal Protocol on Substances that Deplete the Ozone Layer calls for a 50-percent reduction in the use of chlorofluorocarbons (CFCs) by 1995, using 1986 usage levels as baseline.

. The London Amendment. The subsequent London Amendment calls for the complete elimination of CFC use by 2000.

. The Copenhagen Amendment. The proposed Copenhagen Amendment, to be ratified in 1994, accelerates the complete phaseout of CFCs to January 1, 1996.

The tropospheric growth rates of the major anthropogenic source species for stratospheric chlorine and bromine have slowed significantly in response to these international agreements. For example the 1993 CFC-11 annual growth rate was 25 to 30 percent of that observed in the 1970s and 1980s. The total amount of organic chlorine in the troposphere increased by only 1.6 percent in 1992, about half of the rate of increase (2.9 percent) in 1989. Total peak chlorine/bromine loading in the troposphere is expected to occur in 1994, but the stratospheric peak will lag by about three to five years, so stratospheric abundance will continue to grow for a few more years before declining.

Several substitutes for CFCs and other ozone-depleting substances are now being manufactured and used, including hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs). Growth in atmospheric concentrations of HCFCs has been observed for several years and is currently about 7 percent per year. The direct global warming potential of most HCFCs and HFCs are less than those of the compounds they replace, although some HFCs have substantial global warming potentials. Perfluorocarbons, which have been proposed as CFC substitutes in some applications and are by-products of some industrial processes, including aluminum production, have very long atmospheric lifetimes (several thousand years) and are extremely powerful greenhouse gases. Because they are not harmful to the ozone layer, they are not controlled by the Montreal Protocol. Because of their greenhouse effect, however, they will be considered under the Framework Convention on Climate Change.

Ozone

Ozone is an important greenhouse gas present in both the stratosphere and troposphere. In the troposphere ozone is produced from various precursor gases (carbon monoxide, nitrogen oxides, and non-methane hydrocarbons) and as a result of chemical feedbacks involving methane. Tropospheric ozone-a key component of smog-has increased above many locations in the Northern Hemisphere over the last 30 years. This is a cause for concern because tropospheric ozone acts as a strong absorber of infrared radiation and in high concentrations causes respiratory distress in humans. In the Southern Hemisphere, a decrease has been observed since the mid-1980s at the South Pole; in the hemisphere as a whole, data are insufficient to draw strong inferences.

In the stratosphere ozone is continually being formed and destroyed by chemical reactions. Large natural changes occur in stratospheric ozone concentration; for example between summer and winter, a change of about 25 percent can occur at mid-latitudes. Stratospheric ozone depletion occurs if the rate of ozone destruction becomes faster than its rate of formation, either because of natural causes or human activities. Over the past 15 to 20 years, loss of stratospheric ozone caused by CFCs and halons may have partially offset their direct warming effect. Stratospheric ozone depletion is also linked to increases in ultraviolet (UV) radiation.

Stratospheric Ozone Depletion

Long-term global satellite and ground-based monitoring data indicate that stratospheric ozone depletion has been occurring over most of the globe, except in the tropics, since late in the 1970s. The most dramatic evidence of this decline is the springtime ozone hole in the Antarctic. Downward trends of several percent per decade are now observed in all seasons at mid-latitudes (poleward of 20 degrees) in both hemispheres, with winter and springtime declines of as much as 6 to 8 percent per decade observed poleward of 45 degrees. Global ozone depletion worsened significantly in 1992 and 1993, including wintertime depletions of up to 25 percent over populated regions in the high latitudes of the Northern Hemisphere.

The observations of unprecedented and unexpected ozone depletion in 1992 and 1993, coinciding with the period following the eruption of Mt. Pinatubo, have revealed new gaps in scientific understanding and, hence, in prognostic capabilities. While ozone levels may have been perturbed by the Mt. Pinatubo eruption, either by changes in stratospheric temperature and/or circulation or by enhanced heterogeneous chemistry, the magnitude and timing of the recent, large ozone decreases are not fully explained by the current understanding of these effects. Consequently evaluation of the heterogeneous chemistry associated with surface reactions on aerosols through laboratory studies, atmospheric observations, and modeling remains a research priority.

Antarctic Ozone Hole. Each winter the atmosphere over Antarctica is isolated from the rest of the world by the polar vortex. It is dark and very cold, resulting in the formation of clouds in the ozone layer of the stratosphere. When the sun shines on Antarctica again in springtime, chlorine in these clouds causes local depletion of ozone, thus creating the ozone hole. The hole disappears when the Antarctic atmosphere warms up enough to break up the circulation which isolates it from the rest of the world. Ozone-rich air then flows in to replenish the ozone layer over Antarctica. The springtime Antarctic ozone hole has been growing successively larger and more intense since the 1960s. Now the springtime (October) average total ozone values over Antarctica are 50 to 70 percent lower than those observed in the 1960s. In 1993 the ozone hole over Antarctica produced the lowest values of ozone ever recorded anywhere in the world. The ozone hole is expected to reach its most severe levels early in the next century, and recovery is estimated to take 70 years.

Environmental Implications. Significant increases in ultraviolet (UV) radiation have been observed in conjunction with periods of intense ozone depletion. Analysis of fauna living in the Antarctic region, analysis of health data, and field and laboratory experiments indicate that increases in UV levels may have significant deleterious impacts on human health, fish populations, and, if sustained, most of the earth's ecosystems. In humans and other terrestrial and aquatic organisms, impacts can include immune system suppression, sunburn, cataracts, lesions, reduced vitamin D synthesis, and cancers which can result in reduced fitness and death. In plants UV can inhibit the photosynthetic process and result in the death of organisms.

Changes in UV exposure also relate to issues concerning changing species diversity and agricultural productivity and induce adverse effects on materials such as plastics. The 1993 springtime ozone hole over Antarctica allowed record levels of UV light to reach Antarctica. At one Antarctic monitoring site, UV-B, the part of the spectrum most harmful to life, was recorded at levels 44 percent higher than in 1992. Investigations are now underway on the impact that the increased UV might have on life on and around Antarctica, and on whether animals and plants may have mechanisms to avoid harm from increased UV. Current UV levels have already reduced productivity of ocean phytoplankton-microscopic plants that comprise the base of the Antarctic food chain-by 6 to 12 percent in areas affected by the ozone hole.

Stratospheric ozone depletion is also linked to changes in the surface climate. Loss of lower-stratospheric ozone is predicted to lead to a cooling tendency at the surface. As a result of this effect, ozone decreases offset some of Mt. Pinatubo eruption, either by changes in stratospheric temperature and/or circulation or by enhanced heterogeneous chemistry, the magnitude and timing of the recent, large ozone decreases are not fully explained by the current understanding of these effects. Consequently evaluation of the heterogeneous chemistry associated with surface reactions on aerosols through laboratory studies, atmospheric observations, and modeling remains a research priority.

The greenhouse warming of the halocarbons that caused the ozone change. Such indirect couplings complicate projection of changes in the global climate.

The United Nations Montreal Protocol (1987) and its amendments are being implemented to phase out production of ozone-depleting compounds. Even if the control measures are fully implemented, however, ozone depletion will continue for nearly another decade. Because of the long atmospheric lifetimes (up to 100 years) of many of the halocarbons, the earliest recovery of the Antarctic ozone hole is several decades away, and a return to near-natural atmospheric levels of chlorine and bromine, and therefore of ozone, will take centuries.

Aerosols

Modeling studies suggest that, in contrast to greenhouse gases, anthropogenic particles in the atmosphere derived from sulfur dioxide emissions from coal and oil combustion and heavy industrial processes and from biomass burning can lower surface temperatures. Research on the radiative effects of these atmospheric aerosols is important to understand whether aerosols may be, in the near-term, offsetting the enhanced greenhouse effect of carbon dioxide. Recent studies suggest that the hemispheric asymmetry in this century's warming may be due, at least in part, to the preferential presence of sulfate aerosols in the Northern Hemisphere as a result of industrial emissions patterns.

Natural Factors

Natural factors can exert positive or negative radiative forcings. For example since about 1850, a change in the sun's output may have resulted in positive radiative forcing. In contrast some volcanic eruptions, such as that of Mt. Pinatubo in June 1991, result in short-lived (a few years) increase in aerosols in the stratosphere, causing a large, but short-lived negative radiative forcing. The effect of the Mt. Pinatubo eruption has been detected in the observed temperature record.

Climate Change Indicators

The accumulated evidence suggests that global climate change may be occurring. Among the indicators changes in surface air temperatures provide the most direct evidence. Global mean surface temperature, as indicated by the long-term measured climate record, has increased between 0.3 and 0.6 degrees Celsius over the past century. The observed warming over parts of the Northern Hemisphere mid-latitude continents largely characterized by increases in minimum (night-time) rather than maximum (day-time) temperatures. Scientists and governments around the world agree that if the current rate of increase in anthropogenic emissions of greenhouse gases continues, the global mean temperature will likely warm between 1.5 and 4.5 degrees Celsius over the next century.

Additional evidence for global climate change can be gleaned from observational and satellite records of precipitation over land areas in middle latitudes and in the tropics, areal extent of snow cover, date of snow cover disappearance in the Arctic, trends in sea-ice extent in the Arctic and Antarctic regions, melting of glaciers outside the polar zone, and sea-level rise.

Land Use and Global Climate Change

Alterations of natural systems-clearing land for agriculture, logging forests, or reclaiming swamps-have impacts on emissions and absorption of greenhouse gases but consequences whose magnitude is uncertain. Improved predictions of the response of terrestrial ecosystems to changes in temperature, rainfall, solar radiation, especially UV radiation, and changes in carbon dioxide concentrations will enable the development of management strategies for reducing damage to valuable ecosystems.

Why is Climate Change an Issue

The predicted increases in global mean temperature are likely to lead to shifts in precipitation patterns and rising sea level. Although the implications of these changes is not fully understood, it is climate change that poses the most serious threat to human health, global productivity, and worldwide economic stability.

Prospective changes in precipitation patterns from climate change are predicted to lead to important shifts in world agricultural, forestry, and grassland regions and in the availability of water resources, with the possibility of altering long-established patterns of land use. The growth rate of some plants might be increased in the presence of additional carbon dioxide-called the -fertilization effect-. Together these changes have the potential to cause important shifts in habitat for flora and fauna. Although average global food productively may not be affected adversely by climate change, local effects, especially in developing countries, could lead to hunger, malnutrition, and large-scale human migrations.

Climate change also poses a threat to forestry and fishery resources. Recent studies suggest that forest health may be impacted by negative synergisms among depositional pollutants (such as acid rain), global change parameters (such as elevated carbon dioxide), and biotic stresses (such as insect feeding). Slight changes in salinity or temperature may impact adversely larval stages of fish, the most vulnerable life stage to environmental change.

The warming of the oceans and the melting of icecaps and glaciers will result in sea level rise. The amount of sea level rise over the next century is projected to be tens of centimeters (several times the rate of rise in the recent past), which could lead to coastal flooding, the loss of valuable wetlands, and increased threats to coastal areas from storm surges and hurricanes.

Although there has been little research to date on the human health effects from climate change, such effects could range from increases in vector-borne diseases to higher mortality rates during increased conditions of excessive heat and air pollution, particularly in areas with a high incidence of poverty.

Estimates of human-induced changes in land-cover vary according to the system of land-cover classification used, but to provide some examples, human activities over the last three centuries have resulted in a net loss of approximately 2.32 million square miles or 6 million square kilometers of forest (an area slightly smaller than Australia); a net gain in cropland of approximately 4.6 million square miles or 12 million km2 (an area approximately the size of the United States and Mexico); and a net loss of approximately 0.62 million square miles or 1.6 million km2 of wetlands.

While the direct effects of land-cover changes on global environmental systems are not precisely understood, it is generally accepted that changes in land-cover from human activities have resulted in a net flux of carbon dioxide to the atmosphere approximately equal to the net release over the same period from fossil fuel burning, with land-use and land-cover change representing the largest human source of emissions of nitrogen dioxide. The potential impacts of land-cover changes on climate can only be crudely assessed at present. Much attention has been focused on the effects of deforestation of large areas of tropical rainforest and the resulting changes in radiative forcing through release of carbon into the atmosphere. But land-cover changes also affect regional climate by altering surface runoff, temperature, and wind speed. In the United States, recent trends in land use such as the abandonment of farmland and the increase in forest area should enhance natural absorption of carbon dioxide and methane while reducing emissions of nitrous oxides associated with agricultural fertilizer use.

Program Accomplishments

The focus in 1993 was on global environmental change. President Clinton announced on Earth Day 1993 that the United States was committed to reducing greenhouse gas emissions to the 1990 level by the year 2000. Other accomplishments included a new Climate Change Action Plan and measures to help implement the Framework Convention on Global Climate Change, to protect the stratospheric ozone layer, and to phase out CFC-production.

U.S. Climate Change Programs

The United States is signatory to the 1992 Framework Convention on Climate Change that commits nations to the aim of reducing emissions of greenhouse gases and to the Montreal Protocol that strives to phase out production of CFCs and other ozone-depleting substances. In 1993 the United States undertook a number of programs that helped comply with these agreements.

Earth Day 1993

On the occasion of the 24th Earth Day, April 21, 1993, President Clinton announced that the United States was committed to reducing greenhouse gas emissions by the year 2000 to their 1990 levels and promised a plan to outline steps for achieving these levels. At the 1992 Earth Summit in Rio the United States had joined more than 150 other countries in signing the Framework Convention on Climate Change, whose objectives are to stabilize greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system within a timeframe sufficient to allow ecosystems to adapt naturally to climate change, to ensure that food production is not threatened, and to enable economic development to proceed in a sustainable manner. As of December 21, 1993, the Framework Convention had been ratified by 50 countries and was scheduled to enter into force in 1994.

The Climate Change Action Plan

In October 1993 President Clinton released a blueprint for reducing greenhouse gas emissions, The Climate Change Action Plan. The plan will provide a foundation for the National Report required under the Framework Convention on Climate Change that will describe the policies, programs, and measures the United States is taking to reduce greenhouse gas emissions. The plan targets all greenhouse gases and calls for 50 actions involving many sectors of the economy-industry, transportation, homes, office buildings, forestry, and agriculture. Examples follow.

Forests as Carbon Sinks. One action would reduce carbon dioxide emissions by protecting forests, which are natural greenhouse gas sinks.

Climate Challenge. The Department of Energy (DOE) has formed a new partnership with major electric utilities who have pledged to reduce greenhouse gas emissions. Participating utilities may choose from a range of control options and experiment with innovative ideas to achieve their emission reduction goals.

Climate Wise. As part of this joint program cosponsored by the DOE and the EPA, firms who agree to reduce greenhouse gas emissions set bottom-line emission targets that they can attain using the most cost-effective means available.

DOE Motor Challenge. This new initiative sponsored by the DOE, motor system manufacturers, industrial motor users, and utilities promotes installation of the most energy-efficient motor systems in industrial applications.

EPA Partnerships. Chemical companies are working with the EPA to reduce byproduct emissions of potent greenhouse gases by 50 percent from their manufacturing operations. Aluminum producers joined with the EPA to identify opportunities to reduce greenhouse gas emissions and set targets for real reductions.

U.S. Initiative on Joint Implementation. In addition to reducing greenhouse gas emissions with domestic actions, the Plan lays the foundation for an international response. The Framework Convention encourages countries to explore emission reduction projects together under a program of joint implementation. To gain experience in verifying net emission reductions from certain types of investments in other countries, the U.S. Initiative on Joint Implementation will develop projects to provide greenhouse gas reductions beyond the domestic programs and promote sustainable development. The initiative will advance thinking on issues that need resolution before an international joint implementation effort can be fully mounted.

White House Conference on Global Climate Change

The interagency team assigned by the President to develop a new Climate Change Action Plan relied heavily on public input. For that purpose the team helped organize the White House Conference on Global Climate Change, held on June 10-11, 1993, in Washington, D.C. The conference provided the opportunity for hundreds of recognized experts to offer their suggestions and views. The Climate Change Action Plan was released in October 1993.

Green Technology

The EPA continued to promote green programs that encourage the voluntary introduction of new energy-saving technologies in the marketplace. Accomplishments in 1993 included the following:

Natural Gas Star Program. In March 1993 the natural gas industry and the EPA launched this voluntary partnership to reduce methane emissions from their operations. The 16 participating companies represent 40 percent of U.S. gas transmission and distribution systems. Potential savings from the program could reach 1 million metric tons of methane-the CO2 equivalent of removing 3 million cars from the road.

Energy Star Computers. These computers have a feature that allows the machine to reduce its power consumption automatically or -go to sleep- when not in use. Energy Star computers entered the market in 1993;

Ozone-Friendly Refrigerators. Whirlpool won a $30 million contract in a contest sponsored by an electric utility consortium to provide consumers with energy-efficient, ozone-friendly refrigerators; and

Green Lights Program. This initiative, which encourages companies to replace their existing lighting with new, energy-efficient lighting fixtures, grew to over 1,000 participants in 1993.

Phaseout of Ozone-Depleting Substances

The United States continued to make progress in implementing its regulatory schedule for the phaseout of ozone-depleting substances (ODS). The regulatory implementation schedule, which meets domestic and international deadlines for the phaseout, takes a two-pronged approach:

. ODS Phaseout. Complete the phaseout of Class I ozone-depleting substances by the end of 1995, and

. Significant New Alternatives Policy (SNAP). Implement the SNAP, which evaluates substitutes or alternatives for ozone-depleting substances based on the ozone-depletion potential of a substance, global warming potential, flammability, toxicity, exposure potential, and economic and technical feasibility.

Freezing Methyl Bromide Production

In January 1993 in keeping with the Montreal Protocol and subsequent agreements, the United States signed a notice of proposed rulemaking (NPRM). In addition to accelerating the phaseout schedule, the proposed rule would list methyl bromide as a Class I substance and freeze its production at 1991 levels.

ODS Labeling Program

A labeling requirement for containers of ozone-depleting substances, for products manufactured with ODS, and for products containing ODS will go into effect in 1994. The following warning will appear on labels: -Warning: Contains (insert name of substance), a substance which harms public health and the environment by destroying ozone in the upper atmosphere.- The EPA will enforce use of the label.

CFC Replacements

Studies on CFC replacement compounds are underway to determine their potential impacts on humans and the environment. The metabolism and toxicity of hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs), for example, are being investigated. Available data indicate that compounds that are rapidly metabolized are more toxic than those that are slowly metabolized. HCFC-132b is metabolized rapidly and yields metabolites that are potent inhibitors of the enzymes used by the body to detoxify many drugs and chemicals. As a result its development has been discontinued. Other research suggests that HCFC-123 may increase susceptibility to hepatitis in sensitive individuals. Computer modeling studies of reactions of CFC substitutes are being conducted to develop models that will predict metabolism rates and identify compounds likely to be poorly metabolized and therefore of little toxic potential. Preliminary results of this research are promising, and the range of compounds to be tested has been expanded. The biospheric transport and fate of CFC substitutes are also being investigated to assess likely future concentrations of these new chemicals in air, water bodies, and soils.

UV Monitoring Network

Substantial progress has been made in establishing a U.S. Interagency Ultraviolet (UV) Monitoring Network. Several federal agencies are either currently operating or are developing UV monitoring networks. Because each of the individual agencies have different research and operational needs for UV data (such as concerns with effects on agriculture, on human health, and on fish and wildlife), each of these networks are using different types of instruments that best address their respective needs. A UV monitoring plan has been developed to ensure that data collected by the individual agency networks are intercalibrated.

International Climate Change Actions

The United States is a major participant in international efforts to understand and assess the state of knowledge about global change issues. Hundreds of scientists from more than 50 countries have participated in recent assessments which have included review of scientific results, environmental impacts, technologies, and economic considerations. These intergovernmental assessments are especially important as they are intended to serve as primary inputs to the many international conventions and protocols that the United States supports, including the Framework Convention on Climate Change, the Montreal Protocol on Ozone, and the Convention on Biological Diversity (see Chapter 6).

The Intergovernmental Panel on Climate Change

The Intergovernmental Panel on Climate Change (IPCC) was established by the World Meteorological Organization and the United Nations Environment Program in 1988. The IPCC produces reports on climate change which characterize agreement and disagreement within the climate change research community on issues of importance to policymakers.

The IPCC has produced the 1990 Assessment covering changes in climate, potential impacts, and response strategies; a 1992 Supplement which updated the 1990 volume in time for consideration by governments at the Earth Summit; and a forthcoming 1994 Special Report focusing on radiative forcing of climate resulting from human emissions of greenhouse gases. That report also includes technical guidelines for evaluating sources and sinks of greenhouse gas emissions and technical guidelines for evaluating the potential impacts of climate change. The IPCC currently is preparing a second comprehensive assessment of climate change and the vulnerability of natural and socioeconomic systems to change, scheduled for completion in 1995.

The IPCC assessment process has been a critical part of establishing scientific consensus on climate change issues, largely because of the extensive involvement of a diversity of national and scientific backgrounds, representation of minority views, extensive peer review, and a commitment to scientific excellence.

REFERENCES

Clinton, W.J. and A.C. Gore, The Climate Change Action Plan, (Washington, DC: Executive Office of the President, October 1993).

Executive Office of the President, Office of Science and Technology Policy, Our Changing Planet: The FY 1995 U.S. Global Change Research Program, A Report by the Committee on Environment and Natural Resources Research of the National Science and Technology Council, (Washington, DC: EOP, OSTP, 1994).

Hickman, L.E. and S.D. Lyles, Sea Level Variation in the United States, 1855-1993, (Silver Spring, MD: U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Ocean Service, 1994).

Intergovernmental Panel on Climate Change, Radiative Forcing of Climate Change: The 1994 Report of the Scientific Assessment Working Group of IPCC, (World Meteorological Organization and United Nations Environment Program, 1994).

U.S. Congress, Office of Technology Assessment, Combined Summaries: Technologies to Sustain Tropical Forest Resources and Biological Diversity, (Washington, DC: GPO, May 1992).

U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Environmental Satellite, Data, and Information Service, National Climatic Data Service, Climate Variations Bulletin, Historical Climatology Series 4-7, Vol. 5, No. 12 (Asheville, NC: DOC, NOAA, NESDIS, NCDC, December 1993).

Storm Data and Unusual Weather Phenomena with Late Reports and Corrections, Vol. 35, No. 12 (Asheville, NC: DOC, NOAA, NESDIS, NCDC, December 1993).

U.S. Department of Energy, Oak Ridge National Laboratory, Carbon Dioxide Information Analysis Center, Trends -93: A Compendium of Data on Global Change, (Oak Ridge, TN: DOE, ORNL, CDIAC, September 1994).

U.S. Department of Energy, Energy Information Administration, Emissions of Greenhouse Gases in the United States 1985-1990, (Washington, DC: DOE, EIA, September 1993).

Energy Use and Carbon Emissions: Some International Comparisons, (Washington, DC: DOE, EIA, March 1994).

U.S. Department of the Interior, United States Geological Survey, At Work Across the Nation: U.S. Geological Survey Yearbook Fiscal Year 1993, (Reston, VA: DOI, USGS, 1993).

U.S. Department of State, Climate Action Report, Submission of the United States of America Under the United Nations Framework Convention on Climate Change, (Washington, DC: GPO, 1994).

U.S. Department of Transportation and U.S. Environmental Protection Agency, Clean Air through Transportation: Challenges in Meeting National Air Quality Standards, (Washington, DC: DOT and EPA, August 1993).

U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards, National Air Pollutant Emission Trends, 1900-1992, (Research Triangle Park, NC: EPA, OAQPS, October 1993).

National Air Quality and Emissions Trends Report, 1992, (Research Triangle Park, NC: EPA, OAQPS, October 1993).

U.S. Environmental Protection Agency, Office of Policy, Planning and Evaluation, Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1993, (Washington, DC: EPA, OPPE, September 1994).

Implications of Climate Change for International Agriculture: Crop Modeling Study, (Washington, DC: EPA, OPPE, June 1994).

U.S. Environmental Protection Agency, Office of Pollution Prevention and Toxics, 1991 Toxics Release Inventory: Public Data Release, (Washington, DC: EPA, OPPT, May 1993).