The extreme weather that has brought snow and bitter cold to much of Europe in recent days is part of a remarkable temperature inversion that has also enveloped the Arctic with unprecedented warmth.
This is the second time this winter that such unusual weather has hit the northern hemisphere. In January, the eastern US and Canada suffered a record-breaking “polar vortex” that brought plunging temperatures and led Niagara Falls to freeze.
Now, as Europe experiences its most intense period of cold for eight years, temperatures at the North Pole have risen above freezing point for several days — up to 30 degrees Celsius higher than normal for this time of year.
Both events may be a consequence of man-made climate change, scientists say, as rapid warming of the far north weakens the band of strong westerly winds that normally circulate around the Arctic. This makes it easier for very cold air to plunge thousands of miles south, while warm winds infiltrate polar regions.
Scientists working for Nasa, the US space agency, say that heat and moisture are moving into the Arctic on two fronts this year — not only through the North Atlantic between Greenland and Europe as in the three previous winters but also from the Pacific through the Bering Strait.
We have seen winter warming events before but they are becoming more frequent and more intense
“We have seen winter warming events before but they are becoming more frequent and more intense,” said Alek Petty, a research associate at Nasa’s Goddard Space Flight Centre in Maryland.
Levels of Arctic sea ice are already at or near record low levels. This winter’s exceptional polar warmth is opening up the ice cover north of Greenland, releasing heat from the water to the atmosphere.
“This is a region where we have the thickest multiyear sea ice and expect it not to be mobile, to be resilient,” Mr Petty said. “But now this ice is moving pretty quickly, pushed by strong southerly winds and probably affected by the warm temperatures, too.”
An international study published in February in the Bulletin of the American Meteorological Society showed how Arctic warming has the paradoxical effect of producing more intense winter cold further south in Eurasia and North America.
“In winter, the freezing Arctic air is normally ‘locked’ by strong circumpolar winds several tens of kilometres high in the atmosphere, known as the stratospheric polar vortex, so that the cold air is confined near the pole,” said Marlene Kretschmer of Potsdam Institute for Climate Impact Research, lead author of the study.
When polar ice melts, more warmth escapes from the ocean into the air — which can affect the atmosphere up to 30km high, weakening the polar vortex. “This allows frigid air to break out of the Arctic and threaten Russia and Europe with cold extremes,” said Ms Kretschmer.
The short-term outlook for north-west Europe, the region most affected by this week’s extreme cold, is that the so-called Beast from the East will soon return to its lair as spring sunshine warms the Eurasian land mass. But predicting the long-term meteorological course of Eurasian and North American winters over coming years and decades is fraught with uncertainty.
If the Arctic continues to heat up faster than latitudes closer to the equator, the north-south temperature differences that help to drive atmospheric circulation in the northern hemisphere will reduce. “If you have a weaker circulation, it may be easier to disturb,” said Laura Wilcox, a climate scientist at the University of Reading. That would allow more extreme weather events to take place as the world warms.
“Our projections show that cold winters in general will become much less common,” she said. But growing climate instability would permit short outbreaks of intense cold to take place like this week’s.
Copyright The Financial Times Limited . All rights reserved. Please don't copy articles from FT.com and redistribute by email or post to the web.