As the sun's rays hit the earth, some of it is reflected back into space and some is absorbed by oceans and soils, which then warm the surrounding air. The atmosphere protects the surface of the earth from high levels of ultraviolet radiation, while carbon dioxide in the lower level prevents heat energy from escaping. Without this warming effect, the earth would be inhospitable to life.

After four billion years of the evolution of life, a delicate balance of the carbon cycle has been achieved. Photosynthetic organisms absorb carbon dioxide and release oxygen. Although plants also give off carbon dioxide during respiration, most of this greenhouse gas is transformed into sugars for energy or conversion to other plant material. When plants rot, the action of decomposers releases carbon dioxide back into the atmosphere.

Fossil fuels, such as coal, oil, and gas, have been storing carbon underground for millions of years. When burned, the carbon reacts with oxygen in the air to form carbon dioxide. By extracting and burning these fuels, humans add SIX BILLION TONS of carbon to the lower atmosphere every year! This has severely upset the equilibrium established by nature's ingenious carbon cycle. As the level of carbon dioxide builds up in the atmosphere, less of the sun's heat can escape into space, causing a warming of the earth. Since the early 1800's, carbon dioxide in the earth's atmosphere has increased roughly 30%, and the global average temperature appears to have risen between 1 and 2 degrees Fahrenheit. Even if we ceased all burning of fossil fuels right now, we would not experience a subsequent cooling, scientist predict, since carbon dioxide stays in the atmosphere for 100 to 200 years. ^[1]

Deforestation also contributes significantly to the greenhouse effect. Methane and nitrous oxide, other greenhouse gases, together contribute almost half as much warming as does carbon dioxide. Sources of methane emissions include rotting wood in swamps, rice paddies, cattle, coal mines, gas pipelines, and landfills. Nitrous oxide is released from chemicals such as those in fertilizers.

According to Ross Gelbspan, "what frightens scientist is the possibility of runaway feedbacks . . ." ^[2] Feedback effects can, in some cases, increase warming of the earth even farther than the initial release of greenhouse gases into the atmosphere. One such feedback effect occurs when ice shelves break up and snow melts, exposing rock. Normally, the white ice surface reflects the sun's heat, but the previously covered rock absorbs this heat and further warms the ice cap, causing more melting and further warming of the planet. In 1995, Antarctica's Larsen ice cap (which is more than 1000 ft. thick in some places) began to break up.

Another predicted feedback causing concern is the release of carbon dioxide caused by increase in forest fires as a result of higher temperatures and more severe droughts. In addition, as the ocean warms (and rises because of thermal expansion); evaporation rates increase. Higher levels of water vapor in the atmosphere causes further warming since water vapor traps heat in the atmosphere.

[1]Carnige Melon website: www.gcrio.org/gwcc/toc.html

[2]The Heat is On, p. 28