Frigid winters in Eurasia predicted

Arctic Ice Melt Doubles Risk of Frigid Eurasian Winters, Study Finds

Mashable,

28 October, 2014

Global warming-related sea ice melt in a portion of the vast Arctic Ocean has doubled the risk of colder and snowier winters in Eurasia since 2004, a new study found. The study is the latest in a spate of recent research to examine the ties between rapid Arctic warming and the rest of the Northern Hemisphere. 

Much of that research is still highly contentious in the mainstream climate science community. Here is what scientists agree on: 

The Arctic is warming at a rate about twice as fast as that of the rest of the globe, and this is rapidly depleting the region's sea ice, mainly during the summer and early all.

Rapid Arctic warming is altering the exchange of heat and moisture between the ocean and atmosphere across the Arctic.

Arctic warming may be helping to alter the broader jet stream, which is a corridor of high winds at about 35,000 feet that acts as a weather highway, blowing from west to east across the hemisphere.

The new study, published Sunday in the journal Nature Geoscience, uses 100 computer models as well as observational data to show that recent trends toward colder winters in much of Russia, China, and portions of eastern Europe may be related to the loss of sea ice in the Barents and Kara Seas.

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The authors of the new study, each of whom works at Japanese research institutions, looked at the influence on the atmosphere of the loss of sea ice in one particular slice of the Arctic. Located to the east-northeast of Norway and off the coast of Murmansk, Russia, sea ice in the Barents and Kara Seas has declined precipitously since the late 1970s, with the biggest departures from average in late summer and early fall.

Global temperature departures from average during February 2014, showing extreme cold in Eurasia (and North America).

IMAGE: NOAA/NCDC
When they ran the computer models under low sea ice scenarios and compared them to simulations using high sea ice cover, they found that low sea ice, which closely matches recent conditions, made the occurrence of an unusually cold winter over Eurasia twice as likely to occur.

The study proposes that there is a link between sea ice melt and an intensified area of high pressure over Siberia, appropriately known as the Siberian high. This strengthened high pressure area, with the counterclockwise flow of air around it, causes a current of frigid air to move from north to south across broad areas of Eurasia, the study says. 

During the past few winters Eurasia has stuck out on global maps as one of the most unusually cold areas on Earth during the winter, and explaining the cooling trend there despite skyrocketing global emissions of greenhouse gases, which warm the atmosphere, has largely eluded researchers. 

Interestingly, the study finds that over the long run, global warming is likely to win out by reducing the likelihood for colder winters in Eurasia toward the end of the century. “... The frequent occurrence of cold winters may be a temporary phenomenon in a transitional phase of eventual global warming,” the study says. 

Average sea ice extent at the end of the summer melt season in September, showing the sharp decline across the Arctic since 1979.

IMAGE: NSIDC
The study says there is a possibility that a stronger Siberian high — also known as a blocking high because it stalls weather systems trying to move into or out of the area — may be the result of a weakened jet stream caused by a reduced temperature difference between the equator and the North pole.

Lead author Masato Mori of the University of Tokyo told Mashable in an email that the study provides “circumstantial evidence” tying reduced sea ice in the Barents and Kara Seas to more frequent atmospheric blocking downstream, over Eurasia. “However,” he says, the “physical relationship is still unclear. Further studies are required.”

The island of Novaya Zemlya, which is north of western Russia. To the left of the island are the clear waters of the Barents Sea, to the right, the still ice-filled waters of the Kara Sea, during June, 2001.

IMAGE: NASA

In other words, there are strong suggestions that sea ice loss is related to cold winters in Eurasia, but the exact reasons why that is, in terms of the physical chain of events from the ocean to Russia and China, has proven elusive so far.

Depending who you ask, study either "seals the deal" or provides little new insight

The new study generally lines up with a hypothesis first put forward by Jennifer Francis, a climate scientist at Rutgers University, and Steven Vavrus, a researcher at the University of Wisconsin.

Francis and Vavrus have argued that Arctic warming and sea ice loss has resulted in a weaker jet stream that is more prone to forming large waves that are difficult to dislodge. A wavier jet stream, they say, can lead to more extreme weather patterns. This hypothesis has received a great deal of publicity in the past few years.

Francis told Mashable that this study, along with a few others that have been published recently, “...seals the deal in establishing this linkage” between Arctic warming and a wavier jet stream.

“This paper… demonstrates that sophisticated models forced only with sea-ice variability in the region north of Scandinavia (Barents/Kara Seas) produce a ridge in the jet stream over the ice-loss region (owing to extra heat transferred back to the atmosphere from the newly ice-free area), which strengthens the downstream surface high-pressure area, and circulates Arctic air southward over central Asia,” Francis says. “This cold wind chills the region and depresses the jet stream southward, creating a stronger ridge/trough pattern, or a wavier jet stream,” she said.

Vavrus also said that the new study fits in with the basic building blocks of their hypothesis, and said it’s the “most comprehensive” study yet on the link between sea ice loss in parts of the Arctic Ocean with colder than average winters in parts of Europe and Asia.

However, other researchers question the physical evidence behind Francis and Vavrus’ hypothesis as well as the new study. 

Kevin Trenberth, a senior scientist at the National Center for Atmospheric Research in Boulder, Colorado, published a study in August in which he and his colleagues argued that the extreme cold in Eurasia, along with other extreme weather events during the past few years, are tied to fluctuations in ocean conditions and precipitation patterns across the Pacific, rather than the Arctic. 

He sees a wavier jet stream and winters in which the Arctic is warmer than average, while Eurasia is cooler than average, to be a consequence of Pacific Ocean conditions. 

Regarding the new study, Trenberth told Mashable that he doesn’t see anything new. “There is no question that the European anomalies were related to the atmospheric circulation and NAO,” he said, using the acronym for the North Atlantic Oscillation, which is a pattern of atmospheric pressure across the Atlantic Ocean that influences winter weather in the U.S. and Europe.

“But does this paper tell us anything?”

Stay tuned, as this study is far from the final word on the topic