Greenhouse gases are chemical compounds that are found in the Earth’s atmosphere. These gases allow sunlight to enter the atmosphere freely. When sunlight strikes the Earth’s surface, some of it is reflected back towards space as infrared radiation (heat). Greenhouse gases absorb this infrared radiation and trap the heat in the atmosphere. Over time, the amount of energy sent from the sun to the Earth’s surface should be about the same as the amount of energy radiated back into space, leaving the temperature of the Earth’s surface roughly constant. This process is the fundamental cause of the greenhouse effect. It is named this way because of a similar effect produced by the glass panes of a greenhouse. The primary greenhouse gases in the Earth's atmosphere are water vapour, carbon dioxide, methane, nitrous oxide, and ozone. In the Solar System, the atmospheres of Venus, Mars, and Titan also contain gases that cause greenhouse effects. Greenhouse gases greatly affect the temperature of the Earth; without them, Earth's surface would be on average about 33 °C (59 °F) colder than at present.
The Industrial revolution has substantially increased the levels of carbon dioxide in the atmosphere through the burning of fossil fuels. Greenhouse gases are also accumulating in Earth’s atmosphere as a result of human activities, causing surface air temperatures and sub-surface ocean temperatures to rise.
The impact of Green House Gases on the global climate since the Industrial Revolution has been complex. Though emissions of greenhouse gases, like carbon dioxide and methane have had a net warming effect, emissions of sulphate, aerosoles have had a net cooling effect.
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