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 of "scrubbing" of this carbon dioxide in the atmosphere, that the earth would return to a greenhouse state. Some scientists believe that the end of the snowball Earth caused an event known as the Cambrian Explosion, which produced the beginnings of multi-cellular life. However some biologists claim that a complete snowball Earth could not have happened since photosynthetic life would not have survived underneath many meters of ice without sunlight. However, it has been observed that, even under meters of thick ice around Antarctica, sunlight shows through. Most scientists today believe that a "hard" Snowball Earth, one completely covered by