Identity and briefly discuss the major greenhouse gases? Solution A greenhouse gas (often abbreviated as GHG) is a gas that both absorbs and emits radiation in the infrared range, commonly called thermal radiation or heat. When present in the atmosphere, these gases trap radiation in the form of heat, causing a warming process called the greenhouse effect. The presence of four major greenhouse gases, namely water vapor (H2O), carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) in the Earth\'s atmosphere keeps the average temperature of 15.