About 200,000 people from across the world signed up and 50,000 have now run the programme -- which plots the global climate from 1920 to 2080 -- long enough for the results to be statistically significant.

Each programme was slightly different, so that a very broad range of possible outcomes was covered.

"People need to understand this is not a worst-case scenario. This is what we are increasingly confident will happen in the absence of substantial cuts in greenhouse gas emissions," said project co-ordinator Nick Faull of Oxford University.

The initial results will be presented by renowned wildlife broadcaster David Attenborough in a BBC programme -- Climate Change: Britain Under Threat -- on Sunday, giving snapshots of Britain in 2020, 2050 and 2080.

They show flooding will become widespread and regular and that heatwaves like the one which struck Europe in 2003 killing thousands of people will become the norm, making conditions in millions of homes and London's creaking underground system unbearable.

"By using the computers of many tens of thousands of people around the world, all of whom will be affected by climate change in some way or another, we have created the largest "virtual" supercomputer dedicated to climate change that the world has ever seen," said Bob Spicer, chief academic for the programme.

"We have been able to do calculations that even on a normal supercomputer would have taken decades to complete," he added.