A greenhouse gas is a gas that absorbs and emits radiant energy within the thermal infrared range causing the earth's atmospheric temperature to rise. The most important greenhouse gas in the atmosphere is Carbon Dioxide (CO2) as it has the highest global warming potential. It means that among all the greenhouse gases, CO2 would stay for the longest in the atmosphere and raises the temperature of the atmosphere at a faster rate. Other greenhouse gases include Methane, Nitrous oxide, Chlorofluorocarbons etc.