Climate is a way of describing the patterns of weather over a long period. We can describe the conditions we expect with each season and the likelihood of extreme events such as storms and droughts.

The earth's atmospheric conditions are driven by the radiation (heat, light etc) received from the sun. Over geological time the radiation received has varied and the atmospheric systems have responded to these changes. This variation is seen in changes of climate. Records from ice core data, geological records, studies of soil and vegetation have produced evidence of past changes in the global climate.

The Climate Change that we are presently seeing is believed by the majority of scientists to be caused by Greenhouse Gases released by people. Most of these gases come from the burning of coal, oil and natural gas. This Climate Change is happening much more rapidly than any other change in the Climate that we know of from studying the past, through ice cores, tree growth, chemical analysis and fossils.

Naturally occurring greenhouse gases, most importantly, water vapour, in our atmosphere have helped to provide conditions that are suitable for life. Greenhouse gases allow the radiation from the sun to penetrate to the earth, but trap the re-radiated heat from the earth's surface. This leads to a warmed layer of atmosphere that keeps temperatures on the earth's surface within an appropriate band for human comfort. Without the atmosphere the temperature at the earth's surface would be -18º C.

These are the most important greenhouse gases, listed with the main source that causes the emissions:

This shows the Greenhouse gas effect in more detail:

Changes in greenhouse gas concentrations have begun to cause more of the sun's radiation to be trapped, increasing the temperature of the earth's atmosphere.

Questions to ask - click on the links below to find out more.

• What evidence is there that climate change is occurring?
• How can we stop or slow further change?
• What changes are likely to occur and what can we do to prepare?