Ability to absorb infrared light: Every molecule absorbs energy. ... Only gases that are able to absorb what infrared light is left over will contribute significantly to climate change. Methane can absorb the infrared light that water vapor leaves behind, which contributes to its higher climate change potential.
The greenhouse effect causes some of this energy to be waylaid in the atmosphere, absorbed and released by greenhouse gases. Without the greenhouse effect, Earth's temperature would be below freezing. It is, in part, a natural process.