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The Greenhouse Effect and Greenhouse Gases

Carbon dioxide present in the earth's atmosphere contributes to the Greenhouse Effect.

Illustration of the Greenhouse Effect
Illustration of the Greenhouse Effect
Source: World Book illustration by Lawrie Taylor
Illustration of the Greenhouse Effect
Source: World Book illustration by Lawrie Taylor
Click to enlarge

Greenhouses work well to promote plant growth because the energy from the visible rays of the sun can be used by plants in the greenhouse to fuel photosynthesis, and the greenhouse glass traps heat to keep the plants warm. Visible sunlight entering the greenhouse turns into long wave (infrared) radiation after striking surfaces in the greenhouse, and then much of the infrared radiation is reflected back by the same greenhouse glass that let the visible rays in. To some extent, the earth's atmosphere functions just like the clear panes of a greenhouse; hence the name "Greenhouse Effect." Visible sunlight travels through the atmosphere and warms the earth. That warmth radiating off the earth is reflected by the atmosphere back to the earth. The Greenhouse Effect is illustrated by the figure to the right.

Carbon Dioxide is one of the Main Greenhouse Gases

The atmosphere is made up of many different gases. Several gases have the ability to reflect the sun's energy radiating from the earth back to the earth as heat. The gases with this capability are known as "greenhouse gases" (GHGs). The main GHGs are water vapor, carbon dioxide, methane, and nitrous oxide. Without some level of GHGs in the atmosphere, the earth would be much colder than it is and life on this planet would be much different.

Global Warming and Greenhouse Gases

GHGs are produced both naturally and by human activity. Most scientists believe that the increase of human-generated GHGs, in particular, the relatively rapid increase in carbon dioxide concentrations beyond what is considered a normal or natural level, is the primary cause of currently observed anthropogenic (human-induced) global warming. Global warming can be defined as a long-term increase in the average temperature of the near surface of the earth's atmosphere. The primary reason for the large increase in carbon dioxide concentrations in the atmosphere over the last few hundred years is the increased use of fossil fuels, which release significant quantities of carbon dioxide when they are burned. Another cause for the increase is land use changes, such as the harvesting of forests in the tropics (because the harvested trees are no longer available to take in carbon dioxide) or intensive agricultural practices that can lead to the loss of carbon from soil.