Without the greenhouse effect we would not be able to live on earth. Greenhouse gas particles act like valves. They let in incoming radiation from the sun, but act as a barrier to reflected outgoing radiation. The atmosphere is warmed by this process.

As it warms it re-radiates long wave radiation some of which is directed downwards and warms the earth's surface. If it wasn't for the blanket effect created by greenhouse gases the earth's surface would be well below freezing point - and decidedly inhospitable.

The dominant greenhouse gas is carbon dioxide, accounting for about two thirds of the warming effect. Other gases include methane, nitrous oxide, CFC's, low level ozone and water vapour.

Greenhouse gas concentrations had remained fairly constant for over 10,000 years - regulating the earth's temperature at a pleasant 15C. However, in the last 100 years our exploitation of world resources has upset this balance.

Through the burning of fuels for electricity generation, industry and transportation, and the destruction of carbon dioxide absorbing forests, we are set to double the carbon concentration in the atmosphere by 2030.

The concentration of these gases has therefore intensified the greehouse effect which many scientists believe is causing global warming.

The ten warmest years on record have occurred since 1983, seven of them since 1990. Global temperature in 1998 was the hottest in historical record. And the earth's average temperature has risen by 0.5C in the last hundred years.

Arguably this is a coincidence but can we afford to take the chance?

Links: Hadley Centre at the Met Office for more climate change data.