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 it is not an appropriate description. For example, it has been hypothesized that large releases of greenhouse gases may have occurred concurrently with the Permian–Triassic extinction event or Paleocene–Eocene Thermal Maximum. Other terms, such as "abrupt climate change", or tipping points could be used when describing such scenarios. A hypothetical runaway greenhouse effect on the earth should not be confused with a greenhouse earth, which has happened in several well-known periods. During 80% of the latest 500 million years, the earth is believed to have been in a greenhouse state due to the greenhouse effect, when there were no continental