Causes of Global Warming  

Global warming is a general term that describes a gradual increase in the earth's average temperature. It results from the "enhanced greenhouse effect" in which heat from the sun enters the Earth's atmosphere and is trapped by greenhouse gases such as carbon dioxide, methane, nitrous oxide and water vapor. Greenhouse gases absorb thermal radiation from the sun that would otherwise escape from the Earth's atmosphere, resulting in an increase in global average temperature.

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Methane molecule--

The methane molecule is the simplest example of how a carbon atom can bond to four other atoms to form a tetrahedral shape. The carbon atom sits at the center, with the four hydrogen atoms at the points of the tetrahedron. Carbon's ability to form four strong bonds is unique among the elements and allows it to form large molecules.

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Carbon dioxide is the most important of these gases because of its tremendous rate of increase and its long residence time in the atmosphere. Emissions of these greenhouse gases have been rapidly accumulating since the industrial revolution due to the burning of fossil fuels (coal, oil and gas) and the clearing of forests, agricultural practices and other land disturbances.

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The current rate of carbon emissions is too high, and residence time too long, to be absorbed by plants and the ocean, so the global temperature increases. Scientists believe that this steady increase in greenhouse gases is responsible for observed 20th century warming and that this warming trend will continue in the future.

                                     

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