Gas in an atmosphere that absorbs and emits radiation at thermal infrared wavelengths
This article is about the physical properties of greenhouse gases. For how human activities are adding to greenhouse gases, see Greenhouse gas emissions.
Greenhouse gases (GHGs) are the gases in the atmosphere that raise the surface temperature of planets such as the Earth. What distinguishes them from other gases is that they absorb the wavelengths of radiation that a planet emits, resulting in the greenhouse effect.[1] The Earth is warmed by sunlight, causing its surface to radiate heat, which is then mostly absorbed by greenhouse gases. Without greenhouse gases in the atmosphere, the average temperature of Earth's surface would be about −18 °C (0 °F),[2] rather than the present average of 15 °C (59 °F).[3][4]
Carbon dioxide is causing about three-quarters of global warming and can take thousands of years to be fully absorbed by the carbon cycle.[9][10] Methane causes most of the remaining warming and lasts in the atmosphere for an average of 12 years.[11] Human activities since the beginning of the Industrial Revolution (around 1750) have increased carbon dioxide by over 50%,[12] up to a level not seen in over 3 million years.[13] The atmospheric methane concentrations have increased by over 150% during the same time period.[14]
^"Climate Change Indicators: Greenhouse Gases". United States Environmental Protection Agency. 16 December 2015. Carbon dioxide's lifetime cannot be represented with a single value because the gas is not destroyed over time, but instead moves among different parts of the ocean–atmosphere–land system. Some of the excess carbon dioxide is absorbed quickly (for example, by the ocean surface), but some will remain in the atmosphere for thousands of years, due in part to the very slow process by which carbon is transferred to ocean sediments.
^"Understanding methane emissions". International Energy Agency. The concentration of methane in the atmosphere is currently over two-and-a-half times greater than its pre-industrial levels
^Prentice, I.C. (2001). "The carbon cycle and atmospheric carbon dioxide". In Houghton, J.T. (ed.). Climate change 2001: the scientific basis: contribution of Working Group I to the Third Assessment Report of the Intergouvernmental Panel on Climate Change. hdl:10067/381670151162165141.