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 cooler globally. The Earth is currently in an icehouse stage, as ice sheets are present on both poles and glacial periods have occurred at regular intervals over the past million years. The causes of an icehouse state are much debated, because not much is really known about the transition periods between greenhouse to icehouse climates and what could make the climate so different. One important aspect is clearly the decline of CO in the atmosphere, possibly due to low volcanic activity. Other important issues are the movement of the tectonic plates and the opening and closing of oceanic gateways. These