Greenhouse gases keep our planet warm. They exist naturally in the atmosphere, heating it by trapping energy that has originally come from the Sun. This process is called the naturalgreenhouse effect. Without the greenhouse gases the surface of the Earth would be as cold as the surface of the Moon, about -18°C. In fact the average surface temperature of the Earth is about 15°C.

Measurements taken from all over the world however, have shown that the global climate is changing. In the last 100 years the atmosphere has warmed up by over half a degree Celsius (°C). Also during this time humans have been releasing extragreenhouse gases, which are the result of burning fossil fuels (like coal, oil and gas). These gases include carbon dioxide, methane and nitrous oxide.

It is thought that the man-made emissions ofgreenhouse gases, from the increased use of fossil fuels, are responsible for some of the global warming during the20thcentury. The extra greenhouse gases in the atmosphere trap more energy and therefore enhance the naturalgreenhouse effect. Greenhouse gases are also released by the exhausts of motor vehicles, and by the cutting down of forests.

If the Earth continues to warm as predicted, the temperature of the Earth's surface may be 3°C warmer by the end of the21stcenturythan it was in 1990, and maybe as much as 6°C. This rapid change in temperature would have manyimpactson the environment and on society. Global warming will affect rainfall,sea leveland the number and strength ofextreme weatherevents such as storms and floods. Human health, agriculture and water supplies will all be affected.

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