Greenhouse Gases

About half of this predicted warming would be due to carbon dioxide (C02) released by burning fossil fuels, making cement, and

cutting and burning forests. Together, these activities release about 8.5 billion metric tons of C02 annually, causing atmospheric levels to rise about 0.4 percent each year.

Carbon dioxide is not the only gas that could cause climate warming. Methane, chlorofluorocarbons (CFCs), nitrous oxide, and other trace gases also absorb infrared radiation and warm the atmosphere. Although rarer than C02, some of these gases trap heat much more effectively. Methane, for instance, absorbs twenty to thirty times as much—molecule for molecule—as C02, and CFCs absorb approximately 20,000 times as much.

Methane is produced by intestinal bacteria in ruminant animals, anaerobic decomposition in wet-rice paddies, pipeline leaks, decaying wastes in landfills, and releases from coal mining. Atmospheric methane is increasing about 1 percent per year. Chlorofluorocarbons, used as spray propellants, degreasing agents, and refrigerants, have been accumulating at 5 percent each year. The biggest shares of greenhouse gases are produced by the developed countries of the world. Together, the United States, the former Soviet Union, Europe, and Japan are responsible for about two-thirds of all potential global warming!

Effects of Global warming

If greenhouse warming occurs, it probably will not be distributed evenly around the globe. Additional ocean evaporation and cloud cover will likely keep tropical coastal areas about as they are now. The greatest temperature changes are predicted to be at high latitudes and in the middle of continents Siberia and the Canadian arctic might experience increases of 10° to 12° C (18° to 22° F). Chicago might go from an average of fifteen to forty-eight days each year above 32° C (90° F). Dallas may have 162 days per year that hot, rather than 100 as it does now. Calcutta, however, where the temperature is always hot, will not get much hotter.

Rising sea levels are among the most ominous potential results of global warming Some oceanographers calculate that thermal expansion alone could raise the sea level by one meter or more in the next century. An even worse scenario is that polar ice caps might melt. There is enough ice in the Arctic and Antarctica to raise the oceans by 30 meters (90 feet) if it all melted. Most of the world's major cities are on coasts only a few meters above sea level. The homes and businesses of about half the world's population would be threatened if the ice caps melt. A large amount of valuable farmland would also be lost. The U.S. Gulf Coast, for instance, would lose about 5,000 sq km, an area the size of Delaware. A few low- lying countries like the Mal-dive islands in the Indian Ocean might disappear entirely.

Many scientists are convinced that global climate change has already begun. They point to the fact that four of the five warmest years on record were in the late 1980 and early 1990s. When the aerosols released by Mt. Pinatubo are finally washed out of the atmosphere, they predict, high

temperatures will return with a vengeance. Others remain skeptical, arguing that recent high temperatures could be just a random anomaly.

Some studies show increasing temperatures; others show that temperatures are stable or even declining slightly. Current climate models fail to adequately represent effects of water vapor, clouds, air currents, ocean circulation, sulfate aerosols, decreasing solar radiation, biogeochemical ocean processes, or the possible growth stimulation of green plants and ocean plankton by higher C02. If the models assumptions are changed slightly, the predictions change from positive (warming) to negative (cooling) trends.

The atmosphere and living organisms appear to have evolved together so that the present chemical composition of the air is both suitable for and largely the result of biological processes. Compression concentrates most gas molecules in a thin layer (the troposphere) near the earth’s surface. The upper layers of the atmosphere, while too dilute for life, play an important role in protecting the earth’s surface by intercepting dangerous,

mutagenic ultraviolet radiation from the sun. The atmosphere is relatively transparent to visible light that warms the earth’s surface and is captured by photosynthetic organisms and stored as potential energy in organic

chemicals.

Heat is lost from the earth’s surface as infrared radiation, but fortunately for us, carbon dioxide and water vapor that are naturally present in the air capture the radiation and keep the atmosphere warmer than it would otherwise be. When air is warmed by conduction or radiation of heat from the earth’s surface, it expands and rises, creating convection currents. These vertical updrafts carry water vapor aloft and initiate circulation patterns that redistribute energy and water from areas of surplus to areas of deficit. Pressure gradients created by this circulation drive great air masses around the globe and generate winds that determine both immediate weather and long-term climate.

Earth’s rotation causes wind deflection called the Coriolis effect, which makes air masses circulate in spiraling patterns. Strong cyclonic convection currents fueled by temperature and pressure gradients and latent energy in water vapor can create devastating storms. Another source of storms are the seasonal winds, or monsoons, generated by temperature differences between the ocean and a landmass. Monsoons often bring torrential rains and disastrous floods, but they also bring needed moisture to farmlands that feed a majority of the world’s population. When the rains fail, as they do in drought cycles, ecosystem disruption and human suffering can be severe.

Many procedures claiming to control the weather are ineffectual, but some human actions—both deliberate and