greenhouse gas: a gas that contributes to the greenhouse effect by absorbing infrared radiation, e.g., carbon dioxide and chlorofluorocarbon.
Greenhouse gases absorb this energy, thereby allowing less heat to escape back to space, and 'trapping' it in the lower atmosphere. Many greenhouse gases occur naturally in the atmosphere, such as carbon dioxide, methane, water vapor, and nitrous oxide, while others are synthetic.
Why a Greenhouse Traps Heat. Since warm air rises, the air on the bottom of the greenhouse that has been heated by sunlight absorption rises to the top and pushes the cooler air there to the bottom. This cooler air is then heated by continuing absorption of sunlight, and the process repeats itself.
