The deep freeze clamping Britain, parts of China and even the American deep south does not mean global warming is a myth, scientists said today.
They insisted the cold snap is just just a blip in the long-term heating trend.
"It's part of natural variability," said Gerald Meehl, a senior scientist at the National Centre for Atmospheric Research in Boulder, Colorado.
With global warming, he said, "we'll still have record cold temperatures. We'll just have fewer of them."
Deke Arndt of the National Climatic Data Centre in Asheville, North Carolina, noted that 2009 will rank among the 10 warmest years for Earth since 1880.
Scientists say man-made climate change does have the potential to cause more frequent and more severe weather extremes, such as heat waves, storms, floods, droughts and even cold spells. But experts did not connect the current frigid blast to climate change.
"We basically have seen just a big outbreak of Arctic air" over populated areas of the Northern Hemisphere, Arndt said. "The Arctic air has really turned itself loose on us."
In the atmosphere, large rivers of air travel roughly west to east around the globe between the Arctic and the tropics. This air flow acts like a fence to keep Arctic air confined.
But recently, this air flow has become bent into a pronounced zigzag pattern, meandering north and south. If you live in a place where it brings air up from the south, you get warm weather. In fact, record highs were reported this week in Washington state and Alaska.
But in the eastern US, like some other unlucky parts of the globe, Arctic air is swooping down from the north. And that is producing temperatures of -16C in Beijing,-41C in mainland Norway, and 18 inches of snow in parts of Britain.
The zigzag pattern arises naturally from time to time, but it is not clear why it is so strong right now, said Michelle L'Heureux, a meteorologist at the Climate Prediction Centre of the National Oceanic and Atmospheric Administration. The centre says the pattern should begin to weaken in a week or two.
Jeff Masters, director of meteorology for Weather Underground, a forecasting service, said he expects more typical winter weather across North America early next week.
That will be welcome news in the South, where farmers have been trying to salvage millions of dollars' worth of strawberries and other crops.
On Miami Beach, tourists bundled up in woollen winter coats and hooded sweatshirts Wednesday beneath a clear blue sky. Some let the water wash over their feet and a few even lay out in bikinis and swimming trunks.