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AnonymMay 19, 2013

What is global warming?

Global warming - A major cause of climate change
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    May 19, 2013

    Global warming is the increase in the average temperature of the Earth's near-surface air and oceans. A warming of the Earth's surface and lower atmosphere that tends to intensify with an increase in atmospheric carbon dioxide. The atmosphere allows a large percentage of the rays of visible light from the Sun to reach the Earth's surface and heat it. A part of this energy is radiated by the Earth's surface in the form of long-wave infrared radiation, much of which is absorbed by molecules of carbon dioxide and water vapour in the atmosphere and which is reflected back to the surface as heat. This is roughly analogous to the effect produced by the glass panes of a greenhouse, which transmit sunlight in the visible range but hold in heat. The trapping of this infrared radiation causes the Earth's surface and lower atmospheric layers to warm to a higher temperature than would otherwise be the case. Without this greenhouse heating, the Earth's average temperature would be only about -73 C (-100 F); even the oceans would be frozen under such conditions. Alternatively, a runaway greenhouse effect like that found on the planet Venus would result in surface temperatures as high as 500 C (932 F). Owing to the rise in atmospheric carbon dioxide caused by modern industrial societies' widespread combustion of fossil fuels (coal, oil, and natural gas), the greenhouse effect on Earth may be intensified and long-term climatic changes may result. An increase in atmospheric concentrations of other trace gases such as chlorofluorocarbons (Freons), nitrous oxide, and methane, due again largely to human activity, may also aggravate greenhouse conditions. A growing number of scientists have predicted that significant alterations in climate patterns will be seen by the turn of the century. They estimate that global average temperatures could increase by as much as 5 C (9 F) by the middle of the 21st century. Such global warming would cause the polar ice caps and mountain glaciers to melt rapidly and result in appreciably higher coastal waters. The rise in global temperature would also produce new patterns and extremes of drought and rainfall, seriously disrupting food production in certain regions. (source Britannica Encyclopedia)

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    May 19, 2013

    Global warming is the rise in the average temperature of Earth's atmosphere and oceans since the late 19th century and its projected continuation. Since the early 20th century, Earth's mean surface temperature has increased by about 0.8 °C (1.4 °F), with about two-thirds of the increase occurring since 1980.The National Academy of Sciences first used global warming in a 1979 paper called the Charney Report, which said: "if carbon dioxide continues to increase, [we find] no reason to doubt that climate changes will result and no reason to believe that these changes will be negligible." The report made a distinction between referring to surface temperature changes as global warming, while referring to other changes caused by increased CO2 as climate change. Global warming became more widely popular after 1988 when NASA climate scientist James Hansen used the term in a testimony to Congress. He said: "global warming has reached a level such that we can ascribe with a high degree of confidence a cause and effect relationship between the greenhouse effect and the observed warming." His testimony was widely reported and afterward global warming was commonly used by the press and in public discourse.

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