While scientists say there is evidence a build-up of gases such as carbon dioxide will likely bring more frequent and severe typhoons, heatwaves and drought in the future, there is uncertainty about whether the effects have already started to appear.

Lack of detailed historical data about the intensity of storms makes it difficult for scientists to judge just how quickly weather patterns are changing.

"Usually we don't associate a particular event to global change, simply because these extreme weather phenomena are occuring essentially year after year," said Liu Shaw-chen, director of Taiwan's Research Centre for Environmental Changes at the government think-tank, Academia Sinica.

While the number of typhoons in the East Asia region have remained relatively constant in the past 50 years, the number of category four and five storms -- the most powerful that cause the most damage -- have risen, Liu said.

The strongest typhoon to hit China in half a century left around 300 people dead or missing last week, flattening thousands of homes, while two other storms swirled past Taiwan and Japan.

"We do expect them to get worse and get more frequent, but it's a gradual change, not a particular event," Liu said.

INCONCLUSIVE OR FACT?

Two weeks ago, the head of the US National Hurricane Centre in Florida told President George W. Bush that data linking a series of devastating storms in recent years, such as Hurricane Katrina last year, to global warming was inconclusive.

But others, including some environmental groups, say research has shown that increasing sea surface temperatures produced by global warming have stirred more intense storms.

"Scientists have to be very conservative and precise when they claim any extreme weather is linked to climate change. That's the difficult part," said Yang Ailun, climate and energy campaign manager for Greenpeace China.

"Obviously, what we can see right now is is the frequency and how severe (typhoons) are, definitely is increasing over time," Yang said.

Meteorological officials in China also see inclement weather changes as evidence of the impact of global warming in the country, which is ranked as the world's number two producer of greenhouse gases, behind the United States.

"China's warming, part of reflection of the global warming, is also linked to less cold currents in winter and heat waves, of which we are seeing more," said, Ren Guoyu, a researcher at the National Meteorological Centre.

Ninety percent of China had experienced higher-than-normal temperatures this year, with southwest Sichuan experiencing the worst drought in 50 years, researchers say.

State media has reported that 17 million people in that region were without clean drinking water due to the drought, while a total of 17.6 million hectares (43.5 million acres) of farmland in China had been affected since April, up 21 percent from the same period last year.

NOT ENOUGH DATA

Meteorologists in Australia, battered annually by crop-destroying cyclones and drought, said it was hard to tell if weather patterns had become more extreme because reliable statistics go back only to the 1960s.

"I think it's probably an unanswerable question for a lot of the different weather phenomena that we observe," said Grant Beard of the Australian Bureau of Meteorology.

Australia has been hit by a series of droughts since the beginning of this decade. One of them, in 2002/03, was the worst in 100 years and decimated crop production.

"When you get down to severe weather events and tropical cyclones, you're somewhat hamstrung by observing systems. We've probably missed quite a few tropical cyclones before the satellite era. We just didn't know they were there," he said.

In terms of drought, Beard said high extremes between wet and dry periods were the norm for Australia.