The Earth’s surface, warmed by the Sun, releases heat into the atmosphere. Some heat is absorbed by greenhouse gases like carbon dioxide and then released to space (A). Some heat goes straight out to space (B). Some heat is absorbed by greenhouse gases and then bounced back to Earth (C). More carbon dioxide in the atmosphere means that more heat will be stopped by greenhouse gases, warming the planet.
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Lisa Gardiner / Windows to the Universe

Earth's Greenhouse Effect

Not all of the energy from the Sun that arrives at Earth can leave easily. After being transformed into heat, it can become trapped by certain gases in the air. This is a natural process called the greenhouse effect. Without any greenhouse effect, Earth’s temperature would be below freezing. However, Earth’s greenhouse effect is getting stronger because we are adding more greenhouse gases to the atmosphere. This is causing global warming.

Sunlight warms the Earth’s surface and than the surface warms the air above it. Some of this heat makes its way back to space. But along the way a lot of it is absorbed by greenhouse gases in the atmosphere. They radiate the heat back to the Earth's surface, to another greenhouse gas molecule, or out to space.

The amounts of greenhouse gases are increasing as fossil fuels are burned, which releases greenhouse gases. Greenhouse gases also make their way to the atmosphere from other sources. Farm animals, for example, release methane gas as they digest food. As cement is made, it releases carbon dioxide.

With more greenhouse gases, heat on its way out of the atmosphere is more likely to be stopped. The added greenhouse gases catch the heat and then send it off in a new direction. Some of the heat will head away from the Earth, some of it will be caught by another greenhouse gas molecule, and some of it will wind up back at the Earth’s surface again. With more greenhouse gases, heat will stick around, warming the planet.

Last modified February 1, 2010 by Randy Russell.

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