Global warming

Global Warming, an increase in the earth’s temperature due to the use of fossil fuels and certain industrial and agricultural processes leading to a buildup of “greenhouse gases” (principally carbon dioxide, methane, nitrous oxide, chlorofluorocarbons, and water vapor) in the atmosphere. Since 1896 it has been known that these gases reduce the escape of the earth’s infrared radiation into space and thus function to maintain the earth’s relatively warm temperature. (This is called the greenhouse effect.) Although there is broad aagreement that human activity, such as burning fossil fuels, has reached a scale that is beginning to influence climate, there is much uncertainty and debate over how much and how fast the climate will warm. Elevated global temperatures could result in coastal flooding and the shifting of major climatic zones and may have serious implications for agricultural productivity.

Since 1850 there has been a mean rise in global temperature of approximately 1 Celsius degree (approximately 1.8 Fahrenheit degrees) and a 228 percent rise in carbon dioxide levels. While most scientists link this temperature rise to the increase in carbon dioxide levels, other scientists argue that this temperature rise could just be part of a natural fluctuation; such fluctuations have been rrecorded for tens of thousands of years and operate in short-term as well as long-term cycles. Because of the difficulty of distinguishing between emissions caused by humans and those caused by natural sources, and a number of other uncertainties, in 1995 the United Nations convened a panel of leading scientists to evaluate the causes and probable effects of global warming. This panel attributed the warming to human influence and predicted that if greenhouse-gas emissions are not reduced, the average global temperature will rise by 1.0 to 3.5 Celsius degrees (1.8 to 6.3 Fahrenheit degrees), with a best estimate of 2.0 Celsius degrees (3.5 Fahrenheit degrees), by 2100, causing sea level to rise by 50 cm (20 in); further warming and ssea-level rise would follow. 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 Meteorology: Human Induced Global Warming.

A number of international efforts have been undertaken to reduce greenhouse-gas emissions, the most recent of which occurred in December 1997. Delegates to an international summit on global warming in Kyōto, Japan, approved an agreement, known as the Kyōto Protocol, rrequiring industrialized nations to limit emissions of greenhouse gases. The pact, signed by officials from 160 countries, requires 38 industrialized nations to accept legally binding limits reducing greenhouse emissions to levels that are an average of 5 percent below the emission levels of 1990. These reduced levels are to be achieved between 2008 and 2012. The United States, the largest emitter of greenhouse gases, pledged to reduce its emissions to 7 percent below 1990 levels, while the European Union pledged to reduce their emissions to 8 percent below 1990 levels.