Using the reach of the BBC and the forecasting techniques of Britain's Meteorological Office, they hope to persuade thousands of people to take part.

Said lead scientist Myles Allen from Oxford University: "If 10,000 people join in, you are already bigger than the world's biggest supercomputer.  

"The more we get, the more accurate will be our predictions. We have got 500,000 climate variations stacked up and ready to go," he told reporters.

Temperatures have risen by 0.6 degrees since the start of the industrial age, and most scientists agree that a rise of more than two degrees could tip the world into a climactic meltdown.

So many variables are involved that the longer the forecasting timescale for the climate models, the higher the uncertainty over the outcome.

"Each person who joins in will get a slightly different model for their computer to crunch, so the more people we get the more confident we can be of our results," Allen said.

Volunteers welcome

Volunteers should go to www.bbc.co.uk/climatechange and follow the instructions.

"Each person who joins in will get a slightly different model for their computer to crunch, so the more people we get the more confident we can be of our results"

Myles Allen
Lead scientist, Oxford University

Allen said the programme only took minutes to download, would not slow people's computers and would use only negligible extra electricity as it would run in the background when the computer was switched on but not being used.

He said it should take an average home computer about three months to complete the full programme that runs a climate model from 1920 to 2080.

"The most important for us is the first few decades of the model to see if it gives an accurate picture of what actually happened in the 20th century," Allen said.
 
Similar experiments boosting computer power by linking thousands of PCs have been carried out in search of extra-terrestrial intelligence and huge prime numbers.