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
Greenhouse and icehouse Earth the greenhouse gas concentration, the Earth would be heading toward a glacial period. Predicted changes in orbital forcing suggest that in absence of human-made global warming the next glacial period would begin at least 50,000 years from now (see Milankovitch cycles). But due to the ongoing anthropogenic greenhouse gas emissions, the Earth is instead heading toward a greenhouse Earth period. Permanent ice is actually a rare phenomenon in the history of the Earth, occurring only in coincidence with the icehouse effect, which has affected about 20% of Earth's history. Greenhouse and icehouse Earth Throughout the Phanerozoic history of the Earth,