Greenhouse gas Greenhouse gas A greenhouse gas is a gas that absorbs and emits radiant energy within the thermal infrared range. Greenhouse gases cause the greenhouse effect. The primary greenhouse gases in Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide and ozone. Without greenhouse gases, the average temperature of Earth's surface would be about , rather than the present average of . The atmospheres of Venus, Mars and Titan also contain greenhouse gases. Human activities since the beginning of the Industrial Revolution (around 1750) have produced a 40% increase in the atmospheric concentration of carbon dioxide (), from 280 ppm
Runaway greenhouse effect that James Hansen's outcome might be possible, but requires ten times the amount of CO we could release from burning all the oil, coal, and natural gas in Earth's crust. Further, Benton and Twitchett have a different definition of a runaway greenhouse; events meeting this definition have been suggested as a cause for the Paleocene-Eocene Thermal Maximum and the great dying. Most scientists believe that a runaway greenhouse effect is actually inevitable in the long term as the Sun gradually gets bigger and hotter as it ages. Such will potentially spell the end of all life on Earth. As the