Millions of people in America and northern Europe are still battling snow and ice, wondering why they are being punished with bitter cold when -- officially -- spring has arrived and Earth is in the grip of global warming.
Yet some scientists, eyeing the fourth year in a row of exceptionally harsh late-winter weather in parts of Europe and North America, suggest warming is precisely the problem.
In a complex tango between ocean and atmosphere, warming is causing icy polar air to be displaced southwards, they contend.
"The linkage is becoming clearer and clearer, I think, although the science has not yet been settled," said Dim Coumou of the Potsdam Institute for Climate Impact Research (PIK) near Berlin.