What is the "Greenhouse Effect"?

The existence of greenhouse gases in the Earth's atmosphere is essential to life on Earth, because in their absence the average temperature would be about 33 degrees centigrade lower than they are today. The temperature of the earth's atmosphere warms and cools in relation to the balance between the amount of radiation from the sun absorbed by the Earth and energy leaving the atmosphere through re-radiation back into space.

Light energy radiates from the sun and impacts the Earth's atmosphere, where some of this energy is reflected back into space by the outer atmosphere. The energy not reflected passes through the space-atmosphere boundary. Of the incoming solar radiation:

• Approximately 30% is reflected back to space by clouds and the surface of the Earth;
• The atmosphere absorbs and reradiates 25% back to space; 
• And the remaining 45% is absorbed by the land and ocean surfaces.

Interestingly, the temperature of the lower atmosphere and the Earth's surface is higher than what would be expected for a planet that is the same distance from the Sun as is the Earth. The reason for this is that different atoms and molecules making up the Earth's atmosphere absorb different types of radiation to varying degrees. Water vapor, carbon dioxide and other greenhouse gases readily trap the radiation of energy from the Earth's surface and lower atmosphere before the energy can be re-radiated back into space. Therefore, the quantity of carbon dioxide and other greenhouse gases residing in the atmosphere impacts the amount of heat absorbed by the atmosphere. Everything else being equal, the more greenhouse gases in the atmosphere, the more energy is absorbed and the warmer the Earth's climate will be.