Background
Although the sun heats the earth’s surface, a large fraction of the sun’s energy is reflected back into space by clouds, ground surfaces, ice, and water. However, certain gases in the earth’s atmosphere, such as carbon dioxide and methane, trap some of the sun’s heat and prevent it from returning to space. The trapped energy warms the earth’s climate, much like glass in a greenhouse. Hence the gases that cause this effect are often referred to as greenhouse gases.
In response to potential environmental problems linked to the emissions of various heat-trapping gases, the United States and many other nations in 1992 signed a treaty aimed at limiting climate change induced by human activity. This treaty, called the United Nations Framework Convention on Climate Change, seeks to stabilize atmospheric concentrations of greenhouse gases at levels that would prevent dangerous human interference with the climate system. Under the 1992 convention, the United States and other parties generally agreed to implement programs aimed at reducing their emissions of greenhouse gases not covered by another treaty, the Montreal Protocol.4 The most important of these warming gases, in declining order, are carbon dioxide, methane, nitrous oxide, and three types of synthetic (manufactured) gases—sulfur hexafluoride, hydrofluorocarbons, and perfluorocarbons.
Source: United States General Accounting Office
Climate Effects, Emissions Trends |
