Stuard McDill / Reuters
Arctic sea ice is a key focus for climate scientists, including this expedition last fall on drift ice some 500 miles from the North Pole.
Remember New York City's 2011 blizzard? Or Florida's 2010 hard freeze? Blame them on the summer.
According to a new study, those are the type of extreme cold events in the northern hemisphere's winter that appear tied to warmer Arctic summers.
It's certainly counterintuitive, the authors acknowledge, and that could be why climate models haven't picked up on the trend identified in the study: The warmer Arctic, along with melting sea ice, create more moisture in the Arctic and that typically leads to more snowfall across northern Eurasia in October -- a key factor in this entire dynamic. That extra snowfall, in turn, alters what's known as the Arctic Oscillation, sending cold blasts down south.
"I don't think you can point to a single event and attribute it to a climate signal," lead author Judah Cohen tells msnbc.com, "but I would say that the warm Arctic probably helped tip the odds" for the 2011 New York City blizzard. "And when you start to consider that five of the largest snowstorms for NYC occurred over the past 10 years ... that becomes harder to explain by chance alone. Instead there must be a reason and the reason we propose is the warm Arctic and the subsequent increase in fall snow cover."
The Arctic sea ice has melted to near-record levels, scientists say, and it could shrink even more. NBC's Brian Williams reports.
The study would seem to be upended by this mild winter, which follows a warm Arctic. So what gives?
"The paper does not claim that every winter will be cold," says Cohen, the director of seasonal forecasting at Atmospheric and Environmental Research, a for-profit weather service.
It turns out Eurasia snow cover in October was low. Why?
The reason "has remained elusive," Cohen says. "All I can say is that the atmospheric pattern was less conducive to the advance of snow cover this October compared to the last two Octobers.
"The snow cover did advance rapidly in November this year," he adds, "however our research has shown that October is the key month; rapid advances in snow cover the other months does not have the same impact."
There is a caveat to the warm summer/cold winter theory.
"If it continues to get much warmer in the fall," Cohen says, "precipitation that currently falls as snow will fall as rain instead, eliminating the winter cooling."
The study was published Friday in the peer-reviewed Environmental Research Letters. Scientists at the University of Massachusetts and University of Alaska contributed as well.
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