OSLO - Hurricane Katrina has spurred debate about global warming worldwide with some environmentalists sniping at President George W. Bush for pulling out of the main U.N. plan for braking climate change.

Experts agree it is impossible to say any one storm is caused by rising temperatures. Numbers of tropical cyclones like hurricanes worldwide are stable at about 90 a year although recent U.S. research shows they may be becoming more intense.

Still, the European Commission, the World Bank, some environmentalists, Australia"s Greens and even Sweden"s king said the disaster, feared to have killed thousands of people in the United States, could be a portent of worse to come.

"As climate change is happening, we know that the frequency of these disasters will increase as well as the scope," European Commission spokeswoman Barbara Helfferich said.

"If we let climate change continue like it is continuing, we will have to deal with disasters like that," she said. She said it was wrong to say Katrina was caused by global warming widely blamed on emissions from cars, power plants and factories.

Sweden"s King Carl XVI Gustaf told reporters he was deeply shaken by the damage and suffering of millions of people.

"It is quite clear that the world"s climate is changing and we should take note," he said. "The hurricane catastrophe in the United States should be a wake-up call for all of us."

Climate change policies sharply divide Bush from most of his allies which have signed up for caps on emissions of greenhouse gases under the U.N."s Kyoto protocol. Bush pulled out of Kyoto in 2001, saying it was too expensive and wrongly excluded developing nations from a first round of caps to 2012.

In July this year, Bush launched a six-nation plan to combat climate change with Australia, China, India, Japan and South Korea focused on a shift to cleaner energy technology. Unlike Kyoto, it stops short of setting caps on emissions.

SEA LEVEL RISE

U.N. studies say a build-up of greenhouse gases is likely to cause more storms, floods and desertification and could raise sea levels by up to a meter by 2100.

Sea level rise could expose coasts vulnerable to storms because levees would be swamped more easily. Some scientists dispute the forecasts and the United States is investing more heavily than any other nation on climate research.

In Australia, the opposition Greens party said Katrina was aggravated by global warming and criticized Bush for pulling out of Kyoto. The United States, the world"s biggest polluter, and Australia are the only rich nations outside Kyoto.

"It demonstrates the massive economic, as well as environmental and social penalties, of George Bush"s policies," Greens leader Bob Brown told Reuters. He did not believe Bush would shift to embrace Kyoto-style caps on emissions.

Concerns were also voiced in Germany.

"The U.S. must be more involved," Gerda Hasselfeldt, a leading German candidate to become environment minister if the conservative opposition wins the September 18 election, told n-tv television.

In the United States, the focus has been far more on tackling the human disaster than on links to climate change.

"People are still reeling from the tragedy," said Katie Mandes, a director at the Washington-based Pew Center, a climate change think-tank. "Politically it"s too early to tell what it will mean for Americans" views."

Ian Johnson, the World Bank"s top environmental official, said Katrina could also be a wake-up call for developing nations, many of which are vulnerable.

An opinion survey published this week showed that 79 percent of Americans feel global warming poses an "important" or "very important" threat to their country in the next 10 years. Worries among Europeans were even higher.

Taken before Katrina in June, the Transatlantic Trends survey showed that Americans felt more threatened than Europeans by terrorism, Islamic extremism, weapons of mass destruction and economic downturn.

Some individual climatic disasters in the past have changed perceptions about climate change. Steve Sawyer, climate change director at Greenpeace, said that ice storms in Canada in the late 1990s had dramatically raised public concerns.

Greenpeace called Katrina a "wake-up call about the dangers of continued global fossil fuel dependency."

Recent research by Kerry Emanuel, a leading U.S. hurricane researcher, shows the intensity of hurricanes -- the wind speeds and the duration -- seems to have risen by about 70 percent in the past 30 years.

"Globally a new signal may be emerging in rising intensity," said Tom Knutson, a research meteorologist at the U.S. National Oceanic and Atmospheric Administration. Higher water temperatures in future may lead to more storms. Hurricanes need temperatures of about 26.5 C (80F) to form.

Additional reporting by Michael Perry in Sydney, Elaine Lies in Tokyo, Jeff Mason and Paul Taylor in Brussels, Iain Rogers in Berlin, Timothy Gardner in New York