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Arctic Warming May Not Be Altering Jet Stream: Study

A new study calls into question the widely-publicized hypothesis that rapid warming of the Arctic climate, including the precipitous loss of summer sea ice cover, is altering weather patterns throughout the Northern Hemisphere. Specifically, the study, which will be published in a forthcoming issue of Geophysical Research Letters, challenges the findings of previous studies that showed a slowdown in the speed and changes in the shape of the jet stream.

In doing so, the study provides additional insight into a nascent area of research regarding how Arctic warming will affect weather patterns in the midlatitudes, notably the U.S. and Europe. As with other emerging scientific issues, consensus on the connections between Arctic warming and midlatitude weather is unlikely anytime soon, but each study can be viewed as providing more clues for future studies.

Much of the current focus centers around the jet stream, which is a channel of fast-flowing air at high altitudes that helps steer weather systems from west to east across the Northern Hemisphere, and it is powered by the huge difference in air temperatures between the equator and the poles. 

Example of a blocked jet stream pattern that led to extreme weather across the U.S. in March 2012.
Credit: Weather Underground.

Researchers such as Jennifer Francis of Rutgers University and Steven Vavrus of the University of Wisconsin have published studies showing the temperature gradient between the equator and the North pole has shrunk causing changes to the jet stream. The main reason behind this is that the Arctic has warmed at twice the rate of the rest of the Northern Hemisphere, a phenomenon known as Arctic amplification. One of the main causes for the increased warming in the Arctic is melting sea ice, which has declined precipitously since 1981 and hit a record minimum last year.

The research shows that the weaker gradient slows the speed of the jet stream in particular seasons and causes it to meander more than usual and make unusual turns like a tourist wandering through Times Square. Francis’ work has also tied rapid Arctic warming, also known as “Arctic amplification,” to an increase in blocked or stuck weather patterns that have been associated with deadly extreme weather events such as the Russian heat wave of 2010, heat and drought in the U.S. in 2012, and even Hurricane Sandy.

The new study, by Elizabeth Barnes of Colorado State University, calls this research into question by showing that what Francis, Vavrus, and others have shown may just be an artifact of their research methods.

NASA computer model animation showing the evolution of a large dip in the jet stream.

In examining trends in the waviness and speed of the jet stream, as well as the number and location of atmospheric blocking events, the study found that the evidence does not support many of the conclusions made in previous studies. Specifically, the study found no significant change in the waviness of the jet stream has been observed based on 30 years of data.

The study concluded that previous research might have construed changes in the height of different layers of the atmosphere for changes in the waviness of the jet stream. The height of specific atmospheric layers are tracked because they correspond to different weather indicators. As the atmosphere warms and air expands, the height of a given layer, measured using its pressure level, also rises. In recent years, the average height of air pressure surfaces has been increasing in the high latitudes, which is consistent with the warming climate.

“This work highlights that observed trends in midlatitude weather patterns are complex and likely not simply understood in terms of Arctic Amplification alone,” the study said. For example, the study found no statistically significant increase in atmospheric blocking events over the North Atlantic, which “suggests that Arctic Amplification over the past 30 years has not had a quantifiable impact on slow-moving weather patterns over North America or the North Atlantic.”

In an email message to Climate Central, Francis said the new study does not significantly contradict her research tying Arctic warming to extreme weather patterns well outside of the Arctic.

“The mechanisms linking Arctic amplification with large-scale circulation patterns are clearly not simple and we still have much to learn. These new results provide additional insight into those linkages,” she said.

However, Francis found fault with parts of the new study. She said that the 30 years of data that Barnes used in her research might hide some of the effects of Arctic amplification, since much of the warming and sea ice loss has taken place in just the past 15 years.

“Because Arctic amplification has emerged from the noise of natural variability only in the last 15 year or so, it is not surprising that its influence would not drive 30-year trends in a statistically significant way,” she said.

Demonstrating the heightened interest in this area of emerging research, on September 12, the National Academy of Sciences is scheduled to hold a workshop in College Park, Md., on new scientific findings related to ties between Arctic warming and midlatitude weather patterns.

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By Eric Peterson (Front Royal, VA 22630)
on August 22nd, 2013

‘However, Francis found fault with parts of the new study. She said that the 30 years of data that Barnes used in her research might hide some of the effects of Arctic amplification, since much of the warming and sea ice loss has taken place in just the past 15 years.”

A 15 year period is generally too short to make climate-related claims.  As Francis points out in one of her videos, the past 15 years have seen a hiatus in warming at lower latitudes while warming has continued at the north pole.  In her view this means that the north-south temperature contrast decreases leading to various effects.  In my view, there is an overall natural lull in warming and the continued Arctic warming is left over from the prior worldwide warming with a lag due to ocean warming.

As evidence we see a lot less ice in the Barents sea north of Europe but often see a lot more around Alaska in winter.  The Barents sea has a lot of influence from the warmed Atlantic while the Pacific has fluctuated into a cooler mode.  I don’t believe anything has emerged from the Arctic other than a gradual decrease in the summer ice with a few outliers like last year.  Her view is that last year was part of an ongoing trend of dramatic ice loss and that this year is a cooler outlier.

As for her central claim that AA increases the amplitude of Rossby waves, I think that is speculative.  She admits as much in her video.  The certainty of that claim has been exaggerated in many news stories.  I think about it like this: The polar jet as a lot of influences particularly from the stratosphere and particularly from uneven temperature in stratosphere.  The stratosphere has a large amount of solar influence.  It seems quite unlikely that a bit of warming at the surface will have much influence.

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By Camburn (ND)
on August 22nd, 2013

Recent research also shows a very large influence to the jet streams via the UV levels impact on ozone in the Stratosphere.

Short term variations are weather, long term is climate.  15 years is not long enough to demonstrate anything.  If that is the new metric, then we have not statistically warmed for 15 years.

Presently there is no convincing argument that potential Arctic warming has a major climate impact.

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By Roger Hill (Worcester, Vermont 05682)
on August 26th, 2013

Dismissing arctic amplification (AA) effects on 45 degree north latitude or mid latitudes would be hilarious if it were not so tragic. 10 out of 10 years with the lowest sea ice on record may not be your scientific statistical trend but it certainly is a trend worth watching.

As daily in field grinding out weather forecasting in New England - blocking systems are very definitely coincident to those same years without as much sea ice.  Nor’easter s that effect us in the Northeast U.S. and adjacent Canada are very much a part of the NAO AO (North Atlantic, Arctic Oscillations) related to blocking systems that have way major effects on our daily weather . 

I think the work Jennifer Francis of Rutgers has done is the best based on the most current trends in sea ice and extra slowing meandering jet stream which any body in meteorology can plainly see daily.

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By John Harkness
on August 27th, 2013

Given the exponential rate that sea ice volume is being lost in the Arctic, it is reasonably safe to say that we will have an essentially ice free Arctic Ocean in the next very few years.

I just have to repeat (and paraphrase) a phrase that Francis has used:

How could switching the planet from a state that had an essentially ice locked ocean to one that has an essentially newly seasonally ice free ocean NOT have dramatic effects at least on Norther Hemisphere climates?

My question is what is the likelihood that we are on the verge of switching from a three-cell NoHem climatactic structure, to a two or one cell structure—essentially one big Hadley cell.

Isn’t something like this not the inevitable outcome of the radical changes we are putting the Arctic through? Won’t the effects on at least the NoHem climate be dramatic, and the effects on most of world ag likely be catastrophic?

Aren’t we staring down the barrel of a global famine only one or two years away?

Your thoughtful (and ideally realistically comforting) responses will be appreciated.

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By Eric Peterson (Front Royal, VA 22630)
on August 27th, 2013

“blocking systems are very definitely coincident to those same years without as much sea ice”

Here’s a good index of blocking: In 2012 the blocking in October coincided with heat release from refreezing.  But in 2007 there was low Arctic sea ice but virtually no blocking in the fall (or other season).  The number of years with ice and blocking measurements is still too small to rule anything in or out but so far there is very little support for the theory in the data.

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By Eric Peterson (Front Royal, VA 22630)
on August 27th, 2013

Considering we do pretty well without three cells most of the time, there is not much wrong with losing cells some or even most of the time.  The consequences are the same as they always are, more rain in some places, less in others.  Those consequences will mainly be felt in fall when the Arctic matters to the patterns (late fall to early spring) when the heat from refreezing is greatest (all fall).

In spring the Arctic is mostly the same or cooler.  In summer the Arctic is out of the picture weather-wise.  The winter is the most interesting season.  I have the read the papers about how the Arctic “remembers” the anomalous fall warmth, but I’m not quite ready to buy in to that.

Global famine could come from permanent La Nina but I don’t see it happening due to the Arctic producing fall warmth.

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