The Earth is bathed continuously in radiant energy from the sun in the form of light and heat. Some of the heat is absorbed by heat-trapping gases in the atmosphere, and this warms Earth's atmosphere. Some of the light energy from the sun that strikes Earth's atmosphere is reflected back into space. The surface of the Earth absorbs the rest of the light energy and radiates it back again as heat. Some of this heat can be absorbed by the heat-trapping gases.
Carbon dioxide is a major greenhouse gas.
Natural cycles ordinarily keep the levels of carbon dioxide in the atmosphere from changing rapidly. Some carbon is removed from the atmosphere through plant photosynthesis. An equivalent amount of carbon is released into the atmosphere by animals and plants, including organisms that cause decay. These organisms give off carbon dioxide during a process called respiration. The respiration of decay organisms also releases methane, another heat-trapping gas, into the atmosphere.