A gas found in the earth’s atmosphere that traps heat radiated from the surface of the earth, and causes the earth’s temperature to rise. The term comes from the fact that these gases act a little like a greenhouse to limit the loss of heat from a system. The gases do not block high-energy radiation from the sun but they trap lower-energy radiation which would otherwise radiate from the Earth into space.

Many of the gases that occur in the Earth’s atmosphere are greenhouse gases. They include carbon dioxide, methane and water vapour. They occur both naturally and due to human activities. If no greenhouses gases were present, the Earth surface would be about 33°C (91°F) cooler than it is. See also Climate change and Global warming.

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