A United Nations report earlier this year said humans are very likely to be to blame for global warming and there is "virtually no doubt" it is linked to man's use of fossil fuels.

But other climate experts say there is little scientific evidence to support the theory.

In fact global warming could be caused by increased solar activity such as a massive eruption.

Their argument will be outlined on Channel 4 this Thursday in a programme called The Great Global Warming Swindle raising major questions about some of the evidence used for global warming.

Ice core samples from Antarctica have been used as proof of how warming over the centuries has been accompanied by raised CO2 levels.

But Professor Ian Clark, an expert in palaeoclimatology from the University of Ottawa, claims that warmer periods of the Earth's history came around 800 years before rises in carbon dioxide levels.

The programme also highlights how, after the Second World War, there was a huge surge in carbon dioxide emissions, yet global temperatures fell for four decades after 1940.

The UN report by the Intergovernmental Panel on Climate Change was published in February. At the time it was promoted as being backed by more than 2,000 of the world's leading scientists.

But Professor Paul Reiter, of the Pasteur Institute in Paris, said it was a "sham" given that this list included the names of scientists who disagreed with its findings.

Professor Reiter, an expert in malaria, said his name was removed from an assessment only when he threatened legal action against the panel.

"That is how they make it seem that all the top scientists are agreed," he said. "It's not true."

Gary Calder, a former editor of New Scientist, claims clouds and solar activity are the real reason behind climate change.

"The government's chief scientific adviser Sir David King is supposed to be the representative of all that is good in British science, so it is disturbing he and the government are ignoring a raft of evidence against the greenhouse effect being the main driver against climate change," he said.

Philip Stott, emeritus professor of biogeography at the School of Oriental and African Studies in London, said climate change is too complicated to be caused by just one factor, whether CO2 or clouds.

He said: "The system is too complex to say exactly what the effect of cutting back on CO2 production would be or indeed of continuing to produce CO2.

"It is ridiculous to see politicians arguing over whether they will allow the global temperature to rise by 2c or 3c."

The documentary is likely to spark fierce criticism from the scientific establishment.

A spokesman for the Royal Society said yesterday: "We are not saying carbon dioxide emissions are the only factor in climate change and it is very important that debate keeps going.

"But, based on the situation at the moment, we have to do something about CO2 emissions."