LONDON -- A freak heatwave that killed hundreds of people in the United States this month is seen by some scientists as the latest evidence of global warming.


But their view provokes furious debate in the scientific community.


Some believe that weather is just another way of saying "unpredictable," and that its very nature is to be variable. Others are convinced the freak weather is more sinister -- the manifestation of man-made global warming.


The heat wave in the United States this month sent temperatures as high as 41 degrees Celsius in Chicago, while temperatures during a heat wave in southern Spain last week soared to 44 degrees.


Scientists supporting the theory of global warming have been winning the publicity battle. Conferences have been held across the world sponsored by the United Nations, including Rio de Janeiro in 1992 and Berlin earlier this year, to warn of the dangers to climate from increasing emissions of carbon dioxide.


Politicians have promised to seek ways of at least stabilizing these carbon dioxide emissions, which result mainly from the burning of fossil fuels to power cars and fuel power stations.


The accelerating use of fossil fuels has, according to the "warmers," led to a slow but sure increase in world temperatures, as the buildup of greenhouse gases traps heat from the sun that should reflect back into space.


This is said to have steadily raised temperatures and led to more severe and unpredictable weather, like the heavy rain storms in northern Europe this winter. Rising sea levels are also predicted as ice-caps melt, threatening to wipe out some low-lying islands, the warmers say, mainly led by scientists at the UN Intergovernmental Panel on Climate Change.


But even though conventional wisdom states that global warming is a proven fact, many scientists do not accept its validity.


Dr. Jack Barrett of London's Imperial College is one of the doubters.


"To conclude that carbon dioxide emissions are a threat to the environment would be doubtful and premature. Only a closer examination of the atmosphere over a long period and further detailed studies will decide the matter," Barrett said in a recent scientific paper.


The paper caused frissons of anger among scientists.


Sir John Houghton, chairman of Britain's Royal Commission on Environmental Pollution and co-chairman of the IPCC, commenting on Barrett's theory, said, "In fact, the opposite is the case."


Dr. Keith Shine from Reading University's Department of Meteorology said Barrett's ideas were completely at variance with observations. "I profoundly disagree with the conclusions he reaches," says Shine.


But Barrett, from Imperial College's chemistry department, pours thinly veiled scorn on the "warmers'" arguments, saying they are based on unreliable data, misunderstand the self-correcting nature of the Earth's atmosphere and represent science-by-committee.


Barrett notes that IPCC scientists based their theories on the fact that the temperature of the Earth has increased by 0.8 degrees during the 20th century.


"This is within the expected margins of error for such a study. A hard scientific view would be that there has been no discernible change in the Earth's temperature despite the significant increase of 25 percent in the level of carbon dioxide.


"To blame the increase in carbon-dioxide level for this alleged slight temperature increase seems to be a piece of poor scientific judgement that only a large committee could achieve," Barrett said in an interview.


"The IPCC's reports do indicate that the conclusions are not unanimous but none of the doubters' arguments is published. Proper science is not carried out by voting," Barrett said.


Barrett says the world's climate has fluctuated naturally over the centuries. In Roman Britain, the climate was warm enough to allow the cultivation of grapes for red wine in the south.


"In the 20th century, factors influencing the weather have been volcanic eruptions, which put vast quantities of gas and dust into the atmosphere. Another factor is the variation in the strength of the sun depending on sun-spot cycles.


"And what the warmers cast aside -- the effect of variations in temperature in the oceans. Because if the oceans warm up by whatever means -- maybe volcanic activity on the seabed and there's a lot of that -- if the ocean warms up then CO2 will be less soluble, forcing more of it out [into the atmosphere].


"The warmers are possibly putting the cart before the horse. The sea warms up, then the amount of CO2 in the atmosphere goes up, there's a lag of about five months."


Barrett points out with some glee that much of conventional opinion 15 years ago, using similar data, was predicting the Earth was heading for a new ice age.


"Normally scientific argument is rigorous and open, but these fellas at the IPCC publish their own conclusions. It's a hell of a gravy train this, I tell you, which is why they don't like seeing any doubts expressed.


"There is scope here for argument, there are so many uncertainties. It's O.K. for academics to talk about these things and argue bitterly, but it's another to come to a premature decision that will cost governments a vast amount of money."