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
Ocean planet the HZ and the magnitude of their greenhouse effect. Several other surface and interior processes affect the atmospheric composition, including but not limited to the ocean fraction for dissolution of and for atmospheric relative humidity, redox state of the planetary surface and interior, acidity levels of the oceans, planetary albedo, and surface gravity. The atmospheric structure, as well as the resulting HZ limits, depend on the density of a planet's atmosphere, shifting the HZ outward for lower mass and inward for higher mass planets. Theory, as well as computer models suggest that atmospheric composition for water planets in the habitable