GREEN HOUSE EFFECT

The energy that lights and warms Earth comes from the Sun. Short-wave radiation from the Sun, including visible light, penetrates the atmosphere and is absorbed by the surface, warming Earth. Earth’s surface, in turn, releases some of this heat as long-wave infrared radiation.

Much of this long-wave infrared radiation makes it back out to space, but a portion remains trapped in Earth’s atmosphere, held in by certain atmospheric gases, including water vapor, carbon dioxide, and methane. Absorbing and reflecting heat radiated by Earth, these gases act somewhat like the glass in a greenhouse, and are thus known as greenhouse gases.

Only greenhouse gases, which make up less than 1 percent of the atmosphere, offer the Earth any insulation. All life on Earth relies on the greenhouse effect—without it, the average surface temperature of the planet would be about -18°C (0°F) and ice would cover Earth from pole to pole.