Greenhouse gases (GHGs) are gases in the Earth’s atmosphere that trap heat and help keep the planet warm enough to support life. Definition: Greenhouse gases are atmospheric gases that absorb and emit infrared radiation, causing the greenhouse effect — a natural process that warms the Earth’s surface. How It Works: The Sun’s energy reaches Earth as sunlight (shortwave radiation). The Earth absorbs some of this energy and re-emits it as heat (longwave infrared radiation)