More Linkage: Arctic Ice Loss and Winter Extremes

Carbon Brief:

Arctic amplification has been linked with very cold winters in mid-latitude regions of the northern hemisphere. The UK, the US and Canada have all experienced extreme winters in recent years. Just last year, for example, the UK had its second-coldest March since records began, prompting the Met Office to call a  rapid response meeting of experts to get to grips with whether melting Arctic sea-ice could be affecting British weather.

The new study, published in Nature Geoscience, suggests the likelihood of severe winters in central Asia has doubled over the past decade. This vast region includes southern Russia, Mongolia, Kazakhstan, and northern China. And it’s the Arctic that’s driving the changes once again, the authors say.

Pronounced change

The study finds that almost all of the very cold winters in central Asia during the past decade have coincided with particularly warm conditions in the Arctic.

The paper points to sea ice loss in the Barents Sea and the Kara Sea as the cause. These sit to the north of Scandinavia and Russia and to the south of the Arctic Ocean, as shown in the map above.
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The researchers found a ‘pronounced change’ towards very low sea ice concentration in the two seas since 2004. You can see this in the series of blue dots in graph below.

The years with very low sea-ice coincide with very cold winter temperatures recorded in central Asia, as you can see in the graph below.

 

How could this loss of sea ice in the Arctic be affecting mid-latitude winters?

One theory is that the warm Arctic could be influencing the jet stream – a band of fast-flowing air high up in the atmosphere.

Professor Jennifer Francis, from Rutgers University in the US, explains:

“The idea is that ice loss in this area tends to create a wavier jet stream pattern, which causes colder winters in central Asia and blocking patterns that make this weather regime very persistent.”

Arctic links to weather patterns further south is a very new area of research. There is relatively little data to work with as Arctic amplification only emerged as a strong signal in the mid-1990s. However, Francis thinks the amount of evidence is beginning to stack up:

“Based on this new solid and convincing work, along with the others that support the existence of this mechanism, I think we can call it a done deal.”

Temporary phenomenon

So what does that mean for mid-latitude winters in the future?

Despite Arctic sea-ice loss making cold winters more likely, scientists suggest this will be outweighed by winters getting warmer as global average temperature rises.

As Dr James Screen of Exeter University explains:

“As more Arctic sea ice is lost in the future, the warming of the Arctic region gets larger. This warming spreading from the Arctic is large enough to offset (and exceed) any cooling related to change in atmospheric circulation in the long-term.”

The authors of the study agree, saying:

“The frequent occurrence of cold winters may be a temporary phenomenon in a transitional phase of eventual global warming.”

You can see this in the graph from the new paper below. The orange line shows the projected temperature change over central Asia, while the orange bars beneath show the projected frequency of severe winters. Cold winters gradually diminish as temperatures rise through the century.

Bloomberg:

“This counterintuitive effect of the global warming that led to the sea ice decline in the first place makes some people think that global warming has stopped. It has not,” Colin Summerhayes, emeritus associate of the Scott Polar Research Institute, said in a statement provided by the journal Nature Geoscience, where the study is published.

The findings back up the view of United Nations climate scientists that a warmer average temperature for the world will make storms more severe in some places and change the character of seasons in many others. It also helps debunk the suggestion that slower pace of global warming in the past decade may suggest the issue is less of a problem.

“Although average surface warming has been slower since 2000, the Arctic has gone on warming rapidly throughout this time,” he said.