THE GREENHOUSE EFFECT
Many people, including eminent scientists, accept that there is increasing evidence that the world is getting warmer. This is caused by what scientists call the Greenhouse Effect.
Air behaves like the glass of a greenhouse; energy from sunlight passes through and is absorbed by the earth's surface. This warms up and emits heat, in the form of infra-red radiation. In clean air some heat is absorbed by carbon dioxide and water vapour, but most of it escapes back into space.
Polluted air has far more carbon dioxide than clean air. In addition, polluted air has other pollutants such as methane, nitrous oxide and chlorofluorocarbons (CFCs). These are now all called "greenhouse gases". They absorb infra-red heat and radiate it back to the earth. In this way, heat is trapped and warms up the atmosphere.
Carbon dioxide in the earth's atmosphere acts just like the glass in a greenhouse. It allows sunlight to pass through, but it stops infra-red radiation from the earth's surface from escaping back into space.
Since 1850 world temperatures have risen by about 0.5 o C. It is agreed by almost all scientists that this rise is going to continue.
Look at a graphic representation of the greenhouse effect, below (click on the thumbnail for larger view):
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