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How do greenhouse gases warm Earth’s surface and lower atmosphere?

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Grinnell Glacier shrinkage — Global warming A series of photographs of the Grinnell Glacier taken from the summit of Mount Gould in Glacier National Park, Montana, in (from left) 1938, 1981, 1998, and 2006. In 1938 the Grinnell Glacier filled the entire area at the bottom of the image. By 2006 it had largely disappeared from this view.

Greenhouse gases warm Earth’s surface and lower atmosphere through a process known as the greenhouse effect. While Earth’s atmosphere is largely transparent to incoming solar radiation, the planet’s surface absorbs this energy and subsequently emits it back toward space as longwave infrared radiation.12

Greenhouse gases—such as carbon dioxide, methane, and water vapour—possess specific chemical properties that allow them to absorb this outgoing infrared radiation. Because these gases emit the absorbed energy equally in all directions, a significant portion of that heat is reradiated downward toward the surface and the lower atmosphere rather than escaping into space.134

This process increases the total amount of downward-directed radiant energy impinging upon the surface. To maintain thermodynamic equilibrium, the surface and lower atmosphere must emit more radiation than they would in the absence of these gases, resulting in a higher equilibrium temperature. This natural effect is essential for life, as it keeps Earth approximately 33 °C (59 °F) warmer than it would otherwise be.5312