BRUSSELS -- One hot summer does not prove that the planet is warming, but expect a lot more extremes like the heat wave now hitting Europe if the direst climate change predictions come true, weather experts say.

"We cannot say for sure that this is global warming, but the growing frequency of extreme weather events ties in with predictions of global warming," said Asher Minns at Britain's Tyndall Centre for Climate Change Research.

While European holidaymakers bask in one of the hottest Augusts on record, extreme heat and forest fires have killed dozens of people across Europe and drought has hit farmers from the Atlantic to Siberia.

Portugal, the European country worst hit by fires, has declared a state of emergency. Parts of Canada and Russia are also suffering wildfires in unusually hot and dry conditions.

Last summer Germany was hit by similarly devastating floods. Some experts believe that was also an example of the "extreme weather events" that will become more frequent as the so-called greenhouse effect pushes up global temperatures. **** Extremes Increasing****

According to the Intergovernmental Panel on Climate Change (IPCC), drawing on scientific advice from around the world, both drought and floods could be more common due to global warming.

In its last major study, the IPPC said emissions of the gases which trap heat in the atmosphere, causing the greenhouse effect, could raise average earth temperatures by between 1.4 and 5.8 degrees Celsius in the next 100 years.

"As the global temperatures continue to warm due to climate change, the number and intensity of extreme events might increase," the World Meteorological Organization (WMO) said in a statement last month.

But WMO meteorologists, who say it is impossible to forecast weather more than 10 days in advance, warn against jumping to the firm conclusion that we are witnessing global warming. "We don't have enough evidence to say that yet," said the WMO's world climate program director Ken Davidson. "We need more evidence than one or two events."

The picture is likely to become clearer by 2007 when the IPCC is due to produce its fourth assessment of the cause and likely effects of climate change, he said.

Others are more convinced that we are already witnessing the start of a global warming nightmare which environmentalists say could cause massive increases in droughts, deserts and rising sea-levels in the coming decades.

"We cannot directly attribute this one event to climate change...(but) all our models have suggested that this type of event will happen more frequently," said Andy Yeatman, a spokesman for Britain's weather forecaster, the Met Office.

Its computer models have suggested that record hot summers such as August 1995, which used to occur once per century, could happen as often as twice every three years by 2100. **** Ice Age Coming?****

Yet some commentators remain skeptical that human-induced climate change will happen at all, let alone now.

Bill O'Keefe, a board member of Washington-based scientific think-tank the Marshall Institute, said there was no proof that the increase of 0.6 degree Celsius in the earth's temperature in the last century will lead to more extreme weather events. "For at least 15 years, there has been a drum-beat about significant climate change and that human activities and fossil fuel use are causing it and we have an impending apocalypse," O'Keefe said. "In 1977, the National Science Board (a U.S. government panel of scientists) forecast a new ice age."

Such skepticism has influenced U.S. climate policy, which split from the rest of the world when President George W. Bush pulled out of the Kyoto Protocol on reducing greenhouse gases shortly after taking office in 2001.

While European governments are trying to work out how to comply with their Kyoto commitment to cut emissions, the skeptical U.S. administration is putting its efforts into reducing the uncertainties that remain in climate science.

Environmentalists say that could leave it too late to take action to prevent global warming. Sufficient evidence is there to start cutting emissions now, they argue.

Weather experts say it will take time to be sure global warming will happen as predicted. "This is not a question like the one we faced 1,000 years ago -- is the world flat or not," said the WMO's Davidson. "That could be proven by people sailing around the world. "We understand the greenhouse effect. We understand that man is assisting in trapping heat in the atmosphere. But we cannot understand all the effects of this yet."