By David Cotton - first published March 2007

CLIMATE CHANGE is nothing new and there are sceptics who argue that the changes we are currently experiencing are more to do with the long term pattern than with the activities of the human race. However, what is very new is the speed at which the temperature is changing. The current rise is more than ten times faster than can be detected at any time in the past.

Over the last half million years the temperature has varied by almost 10ºC with distinct peaks and troughs. In the last trough, between ten and twenty thousand years ago, ice extended as far south as New York and, with the sea level 100 metres lower, you could walk on dry land from Alaska to Siberia. In the seventeenth and eighteenth centuries, during the "little ice-age", the Thames regularly froze over.

The temperature of the Earth results from a delicate balance between the energy reaching us from the sun and the amount radiated back out again. When anything happens to disturb this balance the temperature changes until a new balance is established. In the past it has been minor changes in our orbit round the sun which have upset the balance, now it is changes to the atmosphere.

The atmosphere plays a major part in maintaining our temperature by preventing some heat escaping back into space. Indeed, if we had no atmosphere at all, the earth’s temperature would be similar to that on the moon, about 30ºC colder that it is now!

Greenhouse Gases (GHGs) in the atmosphere trap energy, as it tries to escape into space, and reflect it back to the surface. Like the glass in a greenhouse these GHGs keep the space below, the "biosphere" we live in, warmer than it would otherwise be. Water vapour is an important GHG but carbon dioxide (CO₂) is the most significant "anthropogenic" one accounting for well over half of mans’ impact on global warming. However, there are other GHGs including methane which is a produced by both ends of a cow as well as from natural gas, landfill sites and marshland. Oxides of nitrogen are produced by vehicle engines and aircraft and chlorofluorocarbons (CFCs) come from refrigeration systems.

During the carboniferous period, 300 million years ago, plants and plankton absorbed CO₂ from the atmosphere and energy from the sun. Over millions of years this was converted into coal, oil or natural gas, the fossil fuels we now use. When we burn them we release all that energy, stored so long ago, and with it all the CO₂ from which the fuels were made - it is this which causes the trouble.

The atmosphere plays a major part in maintaining our temperature by preventing some heat escaping back into space. Indeed, if we had no atmosphere at all, the earth’s temperature would be similar to that on the moon, about 30ºC colder that it is now!

Greenhouse Gases (GHGs) in the atmosphere trap energy, as it tries to escape into space, and reflect it back to the surface. Like the glass in a greenhouse these GHGs keep the space below, the "biosphere" we live in, warmer than it would otherwise be. Water vapour is an important GHG but carbon dioxide (CO₂) is the most significant "anthropogenic" one accounting for well over half of mans’ impact on global warming. However, there are other GHGs including methane which is a produced by both ends of a cow as well as from natural gas, landfill sites and marshland. Oxides of nitrogen are produced by vehicle engines and aircraft and chlorofluorocarbons (CFCs) come from refrigeration systems.

During the carboniferous period, 300 million years ago, plants and plankton absorbed CO₂ from the atmosphere and energy from the sun. Over millions of years this was converted into coal, oil or natural gas, the fossil fuels we now use. When we burn them we release all that energy, stored so long ago, and with it all the CO₂ from which the fuels were made - it is this which causes the trouble.