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Why does the natural greenhouse effect keep Earth warm enough for life?

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World map shaded to show annual carbon dioxide emissions by country in 2022, with China, the United States, and India highlighted as top emitters in dark red. A bar chart below lists the top ten emitting countries by million metric tons. — Greenhouse gas Map of annual carbon dioxide emissions by country in 2014.

The natural greenhouse effect is a vital process that maintains Earth's surface temperature at a level suitable for life. It is important to clarify that this natural phenomenon, driven by atmospheric constituents like water vapour, carbon dioxide, and methane, is distinct from the "enhanced" greenhouse effect caused by human activities.1

The process functions through the interaction between Earth's surface and infrared radiation. While the atmosphere is largely transparent to incoming solar radiation, Earth’s surface absorbs this energy and subsequently emits it back toward space as long-wave infrared radiation. Greenhouse gases absorb a portion of this outgoing radiation and re-emit it in all directions, including back toward the surface and lower atmosphere.123

This mechanism effectively traps heat that would otherwise escape into space, increasing the total radiation directed toward the surface. Without this natural warming, Earth’s average temperature would be approximately 33 °C (59 °F) colder, rendering the planet frozen and likely uninhabitable.132