.. ures have in fact been rising, and the years from 1987 to 1997 were the warmest ten years on record. Most scientists are reluctant to say that global warming has actually begun because climate naturally varies from year to year and decade to decade, and it takes many years of records to be sure of a fundamental change. There is little disagreement, though, that global warming is on its way. Global warming will have different effects in different regions.
A warmed world is expected to have more extreme weather, with more rain during wet periods, longer droughts, and more powerful storms. Although the effects of future climate change are unknown, some predict that exaggerated weather conditions may translate into better agricultural yields in areas such as the western United States, where temperature and rainfall are expected to increase, while dramatic decreases in rainfall may lead to severe drought and plunging agricultural yields in parts of Africa, for example. Warmer temperatures are expected to partially melt the polar ice caps, leading to a projected sea level rise of twenty inches by the year 2050. A sea level rise of this magnitude would flood coastal cities, force people to abandon low-lying islands, and completely inundate coastal wetlands. If sea levels rise at projected rates, the Florida Everglades will be completely under water in less than 50 years. Diseases like malaria, which at present are primarily found in the tropics, may become more common in the regions of the globe between the tropics and the polar regions, called the temperate zones.
For many of the world’s plant species, and for animal species that are not easily able to shift their territories as their habitat grows warmer, climate change may bring extinction. Pollution is perhaps most harmful at an often unrecognized site, inside the homes and buildings where we spend most of our time. Indoor pollutants include tobacco smoke; radon, an invisible radioactive gas that enters homes from the ground in some regions; and chemicals released from synthetic carpets and furniture, pesticides, and household cleaners. When disturbed, asbestos, a nonflammable material once commonly used in insulation, sheds airborne fibers that can produce a lung disease called asbestosis. Pollutants may accumulate to reach much higher levels than they do outside, where natural air currents disperse them.
Indoor air levels of many pollutants may be 2 to 5 times, and occasionally more than 100 times, higher than outdoor levels. These levels of indoor air pollutants are especially harmful because people spend as much as 90 percent of their time living, working, and playing indoors. Inefficient or improperly vented heaters are particularly dangerous. In the United States, the serious effort against local and regional air pollution began with the Clean Air Act of 1970, which was amended in 1977 and 1990. This law requires that the air contain no more than specified levels of particulate matter, lead, carbon monoxide, sulfur dioxide, nitrogen oxides, volatile organic compounds, ozone, and various toxic substances. To avoid the mere shifting of pollution from dirty areas to clean ones, stricter standards apply where the air is comparatively clean.
In national parks, for instance, the air is supposed to remain as clean as it was when the law was passed. The act sets deadlines by which standards must be met. The Environmental Protection Agency (EPA) is in charge of refining and enforcing these standards, but the day-to-day work of fighting pollution falls to the state governments and to local air pollution control districts. Some states, notably California, have imposed tougher air pollution standards of their own. In an effort to enforce pollution standards, pollution control authorities measure both the amounts of pollutants present in the atmosphere and the amounts entering it from certain sources. The usual approach is to sample the open, or ambient, air and test it for the presence of specified pollutants.
The amount of each pollutant is counted in parts per million or, in some cases, milligrams or micrograms per cubic meter. To learn how much pollution is coming from specific sources, measurements are also taken at industrial smokestacks and automobile tailpipes. Pollution is controlled in two ways: with end-of-the-pipe devices that capture pollutants already created, and by limiting the quantity of pollutants produced in the first place. End-of-the-pipe devices include catalytic converters in automobiles and various kinds of filters and scrubbers in industrial plants. In a catalytic converter, exhaust gases pass over small beads coated with metals that promote reactions changing harmful substances into less harmful ones.
When end-of-the-pipe devices first began to be used, they dramatically reduced pollution at a relatively low cost. As air pollution standards become stricter, it becomes more and more expensive to further clean the air. In order to lower pollution overall, industrial polluters are sometimes allowed to make cooperative deals. For instance, a power company may fulfill its pollution control requirements by investing in pollution control at another plant or factory, where more effective pollution control can be accomplished at a lower cost. End-of-the-pipe controls, however sophisticated, can only do so much.
As pollution efforts evolve, keeping the air clean will depend much more on preventing pollution than on curing it. Gasoline, for instance, has been reformulated several times to achieve cleaner burning. Various manufacturing processes have been redesigned so that less waste is produced. Car manufacturers are experimenting with automobiles that run on electricity or on cleaner-burning fuels. Buildings are being designed to take advantage of sun in winter and shade and breezes in summer to reduce the need for artificial heating and cooling, which are usually powered by the burning of fossil fuels.
The choices people make in their daily lives can have a significant impact on the state of the air. Using public transportation instead of driving, for instance, reduces pollution by limiting the number of pollution-emitting automobiles on the road. During periods of particularly intense smog, pollution control authorities often urge people to avoid trips by car. To encourage transit use during bad-air periods, authorities in Paris, France, make bus and subway travel temporarily free. Indoor pollution control must be accomplished building by building or even room by room. Proper ventilation mimics natural outdoor air currents, reducing levels of indoor air pollutants by continually circulating fresh air. After improving ventilation, the most effective single step is probably banning smoking in public rooms.
Where asbestos has been used in insulation, it can be removed or sealed behind sheathes so that it won’t be shredded and get into the air. Sealing foundations and installing special pipes and pumps can prevent radon from seeping into buildings. On the global scale, pollution control standards are the result of complex negotiations among nations. Typically, developed countries, having already gone through a period of rapid and dirty industrialization, are ready to demand cleaner technologies. Less developed nations, hoping for rapid economic growth, are less enthusiastic about pollution controls. They seek lenient deadlines and financial help from developed countries to make the expensive changes necessary to reduce pollutant emissions in their industrial processes.
Nonetheless, several important international accords have been reached. In 1988, the United States and 24 other nations agreed in the Long-Range Transboundary Air Pollution Agreement to hold their production of nitrogen oxides, a key contributor to acid rain, to current levels. In the Montreal Protocol, adopted in 1987 and strengthened in 1990 and 1992, most nations agreed to stop or reduce the manufacture of CFCs. In 1992 the United Nations Framework Convention on Climate Change negotiated a treaty outlining cooperative efforts to curb global warming. The treaty, which took effect in March 1994, has been legally accepted by 160 of the 165 participating countries. In December 1997 at the Third Conference of the United Nations Framework Convention on Climate Change in Japan, more than 160 nations formally adopted the Kyoto Protocol.
This agreement calls for industrialized nations to reduce their emissions of greenhouse gases to levels 5 percent below 1990 emission levels between 2008 and 2012. The United States, which releases more greenhouse gases than any other nation, has traditionally been slow to support such strong measures. The U.S. Senate may be reluctant to ratify the Kyoto Protocol because it does not require developing countries, such as China and India, to meet similar emissions goals. All these antipollution measures have helped stem the increase of global pollution emission levels. Between 1970, when the Clean Air Act was passed, and 1995, total emissions of the major air pollutants in the United States decreased by nearly 30 percent. During the same 25-year period, the U.S.
population increased 28 percent and vehicle miles traveled increased 116 percent. Air pollution control is a race between the reduction of pollution from each source, such as a factory or a car, and the rapid multiplication of sources. Smog in American cities is expected to increase again as the number of cars and miles driven continues to rise. Meanwhile, developing countries are building up their own industries, and their citizens are buying cars as soon as they can afford them. Ominous changes continue in the global atmosphere. New efforts to control air pollution will be necessary as long as these trends continue.