What term describes heat-trapping gases such as methane, CO2, and water vapor?

Heat-trapping gases such as methane, carbon dioxide, and water vapor are called greenhouse gases.

These gases absorb and emit infrared radiation, the long-wave heat energy radiated by Earth’s surface. Sunlight can pass through much of the atmosphere, but the surface sends energy upward as infrared radiation; greenhouse gases absorb some of it and re-emit it in all directions, including back toward the surface.

Water vapor is the most abundant greenhouse gas and supplies much of the natural greenhouse effect, but its global amount mainly responds to temperature. Carbon dioxide and methane are especially important because human activities can directly increase their atmospheric concentrations. Other greenhouse gases include nitrous oxide, ozone, and industrial fluorinated gases.

A greenhouse gas is not the same as an aerosol. Aerosols are tiny particles or droplets that can reflect sunlight, absorb radiation, or alter clouds. Also, “greenhouse” does not mean these gases trap heat exactly like glass; the analogy refers to the atmosphere’s radiative effect, not a sealed container.