National Geographic News
Photo of a man clearing snow with a snow blower.

Azim Fazili clears snow from a Chicago sidewalk on February 17.


Dan Vergano

National Geographic

Published May 22, 2014

The weird winter from which the Northern Hemisphere has just emerged was caused by a curiously warm western Pacific, a climatologist suggests in today's issue of Science, and not by the melting Arctic. (Related: "Earth's Changing Climate.")

Alaska baked, Detroit froze, and England flooded this past winter, which was one of the coldest on record in the American Midwest. Meanwhile western states, notably drought-stricken California, saw record warmth.

Shivering or sodden people had to endure not only the unusual winter but also repeated references from meteorologists to the polar vortex—a frigid low-pressure system that caps the Arctic and is normally contained there by the polar jet stream. Last winter that ring of high-speed winds developed pronounced north-south meanders, allowing Arctic air to flow deep into the United States. (See "What Is the Polar Vortex?")

According to one theory, endorsed this year by White House science adviser John Holdren and some other scientists, the change in the jet stream—and the rotten winter—were ultimately triggered by the warming of the Arctic and the melting of sea ice there. But climate expert Tim Palmer of the University of Oxford says the culprit was the western Pacific Ocean: "What goes on in the tropical Pacific Ocean is of almost global impact."

Compared with the Arctic theory, Palmer's analysis has an upside: It foresees fewer repeats of last winter in our future.

Thunderstorms and Typhoons

Here is Palmer's explanation in a nutshell. During this past winter abnormally warm Pacific Ocean waters stretched roughly from Fiji to Indonesia. They spawned tremendous thunderstorms—and it was the energy of those storms, reaching high into the atmosphere, that rerouted the jet stream. The loopy jet stream sent warm air north toward Alaska and allowed cold air to drop south and freeze the rest of the continent.

Those same warm waters help explain the power of supertyphoon Haiyan, which devastated the Philippines in November. And they're the precursor of what's now forecast to be a large El Niño event later this year. During an El Niño, warm water that's been pushed into the western Pacific by the trade winds comes sloshing back east along the Equator.

Palmer's hypothesis is attracting both endorsement and criticism from other climate scientists.

"I think it is basically right," says climate data expert Kevin Trenberth of the National Center for Atmospheric Research in Boulder, Colorado. Last winter the tropical Pacific saw "incredible amounts of rain," he says, "which likely played a role in setting up the [jet stream] wave patterns across North America."

Mark Serreze, director of the National Snow and Ice Data Center (NSIDC) at the University of Colorado Boulder, agrees. "There is strong evidence of links between the behavior of the jet stream and sea-surface temperature in the tropical Pacific," he says, "compared with much more speculative links with Arctic warming."

The Arctic camp is less impressed with Palmer's paper. "I think it proposes a new mechanism, but there is still a long way to prove the argument," says climate scientist Qiuhong Tang of the Chinese Academy of Sciences in Bejing. "I can hardly find any observation-based evidence in the essay which can support the argument."

Tang and some other scientists, notably Jennifer Francis of Rutgers University, have argued that the warming Arctic and shrinking sea ice have diminished the north-south temperature contrast that drives the jet stream, robbing it of the energy that normally keeps it tightly routed around the Poles.

But, says climate scientist Katharine Hayhoe of Texas Tech University in Lubbock, "the two ideas are not necessarily competitors. They may be complementary."

Global Weirding

In Palmer's view, the past wild winter can be attributed to natural climate variability amplified by man-made climate change. A warm pool in the western Pacific is a natural phenomenon, he says, but global warming kicked the sea-surface temperature up a notch.

"Even a tenth-of-a-degree temperature change in tropical waters can have tremendous weather effects," he adds. (Related: "U.S. Cold Snap Inspires Climate Change Denial, While Scientists See Little Room for Doubt.")

Other scientists remain cautious. "The link to global warming is not obvious to me," says climatologist Gavin Schmidt of NASA's Goddard Institute for Space Studies in New York.

The Arctic explanation for the weird winter points the finger more directly at man-made climate change—and if it's right, we should expect a string of such winters in the future. But we should see fewer of them if Palmer is right that the weirdness came primarily from an abnormally warm western Pacific. Next winter will test his idea: With an El Niño likely on the way, it should be a bit more normal than the last one.

Follow Dan Vergano on Twitter.

t. giobbi
t. giobbi

Odd title. "Is the Pacific to Blame?" is a sensationalist-mainstream-media question that is just designed to get people to read the story. Is that was NatGeo is becoming? 

Other than the title, though, it is a good article. its important to hear multiple scientists debate their hypotheses with each other instead of with climate change denial kooks and non-scientists.

Gregory S.
Gregory S.

I posted about this over a week ago to help explain why there is a new dust bowl developing in the southwest plains, although a nasty post got the whole thread deleted:

What we are seeing
(so far) with current levels of global warming is a disproportionate warming of the arctic ocean from warm air in fluxing from the Pacific. There
is also a decades long Pacific hydrologic cycle that is currently enhancing this effect. With warm air invading the arctic the cold air that normally
bottles up there has to go somewhere and the direction is to lower latitudes, but not uniformly. The result is a block of cold air will set up in a
region of the globe which dramatically alters the weather pattern there for months at a time, rather than days at a time. These blocks of cold air
are easily spotted since they interrupt the jet stream which has to go around these areas of unmoving cold air. The whole process is referred to as
a blocking pattern. The result is an abnormal pattern of repetitive weather (lasting a month or more) which can be wet or dry, depending on which
side of the block you are on. In the winter the temperatures are noticeably colder as well where the block sets up. Global warming seems to be creating
such blocks much more frequently and for much longer periods of time resulting in enhanced regional droughts or floods rather than the usual weather we
expect. The good news is that the Pacific hydrologic cycle enhancing this problem is about to reverse, but most scientists believe that we got a glimpse
of what things are going to be like in the next 10-20 years as global temperatures rise. What lies beyond that is anyone's guess, but it likely will be
something worse unless you live in the arctic and are looking forward to warmer weather.

dave powelson
dave powelson

Thought provoking article.  I appreciate knowing the warm-western-Pacific hypothesis is testable.  This is the way science should proceed.

Anton Uvarov
Anton Uvarov

Don`t worry, according to the 20th Century Fox, The Ice Age can be fun


I just know that this past winter was my first experience in 67 years of  the jet stream holding north to south trends for months on end here in the midwest.   Very strange times indeed.


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