<P> A greenhouse gas (abbrev . GHG) is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range . This process is the fundamental cause of 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 − 18 ° C (0 ° F), rather than the present average of 15 ° C (59 ° F). In the Solar System, the atmospheres of Venus, Mars and Titan also contain gases that cause a greenhouse effect . </P> <P> Human activities since the beginning of the Industrial Revolution (taken as sometime between the years 1740 and 1754) have produced a 40% increase in the atmospheric concentration of carbon dioxide, from 280 ppm in 1750 to 406 ppm in early 2017 . This increase has occurred despite the uptake of a large portion of the emissions by various natural "sinks" involved in the carbon cycle . Anthropogenic carbon dioxide (CO) emissions (i.e., emissions produced by human activities) come from combustion of fossil fuels, principally coal, oil, and natural gas, along with deforestation, soil erosion and animal agriculture . </P>

What are the two most abundant greenhouse gases in the earth’s atmosphere