Global Warming, an increase in the Earth's temperature due to the use of fossil fuels and other industrial processes leading to a build-up of "greenhouse gases" (carbon dioxide, methane, nitrous oxide, and chlorofluorocarbons) in the atmosphere. It has been known since 1896 that carbon dioxide helps stop the Sun's infrared radiation from escaping into space and thus functions to maintain the Earth's relatively warm temperature (this is called the greenhouse effect). The question is whether the measurably increasing levels of carbon dioxide in the atmosphere over the last century will lead to elevated global temperatures, which could result in coastal flooding (through a rise in sea level) and major climatic changes, and have serious implications for agricultural productivity.
Since 1850 there has been a mean rise in global temperature of approximately 1° C (1.8° F), but this rise could just be part of a natural fluctuation. Such fluctuations have been recorded for tens of thousands of years and operate in short-term as well as long-term cycles. The difficulty of distinguishing human-made causes of carbon dioxide emissions from natural sources is one reason why governmental legislation regarding their control has been slow in coming. However, the potential consequences of global warming are so great that many of the world's top scientists have urged immediate action, and have called for international cooperation on the problem. See also Environment.
Greenhouse Effect, term for the role the atmosphere plays in helping warm the Earth's surface. The atmosphere is largely transparent to incoming short-wave solar radiation, which is absorbed by the Earth's surface. Much of this radiation is then reemitted at infrared wavelengths, but it is reflected back by gases such as carbon dioxide, methane, nitrous oxide, halocarbons, and ozone in the atmosphere. This heating effect is at the root of the theories concerning global warming. The amount of carbon dioxide in the atmosphere has been increasing by 0.4 per cent a year because of the use of fossil fuels such as oil, gas, and coal; the slash-and-burn clearing of tropical forests has also been a contributing factor in the carbon cycle. Other gases that contribute to the greenhouse effect, such as methane and chlorofluorocarbons, are increasing even faster. The net effect of these increases could be a worldwide rise in temperature, estimated at 2° to 6° C (4° to 11° F) over the next 100 years. Warming of this magnitude would alter climates throughout the world, affect crop production, and cause sea levels to rise significantly. If this happened, millions of people would be adversely affected by major flooding.