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 effect surface; anti-greenhouse effect is about atmosphere NOT letting radiation in, while letting thermal radiation out, which lowers the equilibrium surface temperature. Such an effect has been cited about Titan A runaway greenhouse effect occurs if positive feedbacks lead to the evaporation of all greenhouse gases into the atmosphere. A runaway greenhouse effect involving carbon dioxide and water vapor has long ago been hypothesized to have occurred on Venus, . The greenhouse effect on Venus is particularly large because its dense atmosphere consists mainly of carbon dioxide. "Venus experienced a runaway greenhouse in the past, and we expect that Earth will