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 The theory contrasts with other experts' views, including that the
freeze was simply a freak natural event or that it was linked to a
thawing of the Arctic in recent years that sent a blast of cold air
south.
"People's reaction when they sit under 10 feet of snow is to say
'this cannot be man-made climate change'," said Professor Tim Palmer
of Oxford University, who published his research in the journal
Science. "But there is a plausible link," he told Reuters.
He said a strengthening of trade winds had led to a build-up of warm
water in the western tropical Pacific, aggravated in recent years by
global warming from man-made emissions of greenhouse gases.
Thunderstorms linked to the warmth in turn disrupted the jetstream,
high altitude winds which flow in vast meandering loops around the
northern hemisphere, and sucked cold air from the Arctic. Detroit,
for instance, suffered record snows and the coldest January since
1977.
Pinpointing the causes of the U.S. chill, when climate change should
make cold winters less likely, would help companies, farmers, city
planners or even home owners wondering if they should invest in
extra roof insulation.
Two other experts were unconvinced by Palmer's study.
ARCTIC LINK
Jennifer Francis of Rutgers University, who wrote in 2011 that a
melting of Arctic ice may cause cold snaps, said the Pacific had a
similar pattern of heavy rainfall in 2011-12 but the winter was mild
in the United States.
"In both cases the jet stream's path was extremely amplified or
wavy, which is exactly the sort of behavior we expect to occur more
frequently in association with rapid Arctic warming," she told
Reuters.
She said that the tropics might also be contributing, but that there
seemed little evidence of this.
Martin Hoerling, of the U.S. National Oceanic and Atmospheric
Administration's Physical Sciences Division, said he reckoned the
most plausible explanation of the cold North American winter was a
"freak of nature".
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He said that there was no sign of a link between Pacific sea
temperatures and U.S. winters in records from 1948 to 2012. And he
also said Francis's Arctic theory "has not been affirmed by
subsequent studies by a variety of researchers".
So far there is limited understanding of how weather in one part of
the world can affect another.
Weather experts agree, however, that the El Nino weather phenomenon
that mainly cools the eastern Pacific Ocean every few years can
cause droughts or downpours on other continents.
Palmer told Reuters that his theory, building on a 1980s study he
wrote suggesting a link between a chill 1976-77 U.S. winter and a
warm Pacific, could be tested because there are signs that an El
Nino will form later this year.
An El Nino would also cool the western Pacific and that meant a cold
U.S. winter was less likely in 2014-15, he said.
A U.N. panel of climate scientists says it is at least 95 percent
probable that human activities, led by burning fossil fuels, are the
main cause of warming since the 1950s, and will cause more heatwaves,
floods and rising sea levels.
(Reporting by Alister Doyle; editing by David Stamp)
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