OSLO Devastating floods in Pakistan and Russia's heatwave match predictions of extremes caused by global warming even though it is impossible to blame mankind for single severe weather events, scientists say.
This year is on track to be the warmest since reliable temperature records began in the mid-19th century, beating 1998, mainly due to a build-up of greenhouse gases from fossil fuels, according to the U.N. World Meteorological Organization (WMO).
"We will always have climate extremes. But it looks like climate change is exacerbating the intensity of the extremes," said Omar Baddour, chief of climate data management applications at WMO headquarters in Geneva.
"It is too early to point to a human fingerprint" behind individual weather events, he said.
Recent extremes include mudslides in China and heat records from Finland to Kuwait -- adding to evidence of a changing climate even as U.N. negotiations on a new global treaty for costly cuts in greenhouse gas emissions have stalled.
Reinsurer Munich Re said a natural catastrophe database it runs "shows that the number of extreme weather events like windstorm and floods has tripled since 1980, and the trend is expected to persist."
The worst floods in Pakistan in 80 years have killed more than 1,600 people and left 2 million homeless.
"Global warming is one reason" for the rare spate of weather extremes, said Friedrich-Wilhelm Gerstengarbe, a professor at the Potsdam Institute for Climate Impact Research.
He pointed to the heatwave and related forest fires in Russia, floods in Pakistan, rains in China and downpours in countries including Germany and Poland. "We have four such extremes in the last few weeks. This is very seldom," he said.
The weather extremes, and the chance of a record-warm 2010, undercut a view of skeptics that the world is merely witnessing natural swings perhaps caused by variations in the sun's output.
Russia's worst drought in decades has led to fires that have almost doubled death rates in Moscow to around 700 per day, an official said. Prime Minister Vladimir Putin announced a grain export ban from August 15 to December 31.
Nearly 1,500 people have died in landslides and flooding caused by months of torrential rains across China, the Ministry of Civil Affairs said.
Baddour said one cause of a shift in monsoon rains in Asia seemed to be a knock-on effect of La Nina, a natural cooling of the Pacific region.
Scientists say it is impossible to pin the blame for individual events from hurricanes to sandstorms solely on human activities led by burning of fossil fuels that release heat-trapping carbon dioxide.
Still, one study concluded that global warming had doubled the chances of heatwaves similar to a scorching 2003 summer in Europe, in which 35,000 people died. Those temperatures could not convincingly be explained by natural variations.
"It may be possible to use climate models to determine whether human influences have changed the likelihood of certain types of extreme events," the U.N. panel of climate scientists said in its latest 2007 report.
That report said it was at least 90 percent likely that most warming in the past 50 years was caused by mankind, a finding questioned by skeptics who have pointed to errors in the report such as an exaggeration of the melt of Himalayan glaciers.
"Warming of the climate is likely to bring more events of this sort," said Henning Rodhe, professor emeritus of chemical meteorology at Stockholm University, of the Russian heatwave.
"But you can't draw the conclusion that this is caused by global warming."
Most countries agreed at a U.N. climate summit in Copenhagen last year to limit a rise in average world temperatures to below 2 degrees Celsius above pre-industrial times, a tough goal since temperatures already rose 0.7C in the 20th century.
The latest round of U.N. climate talks in Bonn, from August 2-6, ended with growing doubts that a global climate treaty could still be agreed as hoped by some nations in 2010 despite deep splits about sharing the burden of curbs on emissions.
U.S. Senate majority leader Harry Reid has all but abandoned climate change legislation this year. The United States, the number two greenhouse gas emitter behind China, is the only major industrialized nation with no law to cut emissions.