Recent Arctic amplification and extreme mid-latitude weather

Author: Judah Cohen, Jason C. Furtado and Justin E. Jones
Date: 
August 17, 2014
Type: 
Journal Article
Venue: 
Nature Geoscience
Citation: 

Authors: Judah Cohen, James A. Screen, Jason C. Furtado, Mathew Barlow, David Whittleston, Dim Coumou, Jennifer Francis, Klaus Dethloff, Dara Entekhabi, James Overland and Justin Jones

URL: http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2234.html

DOI: http://dx.doi.org/10.1038/ngeo2234

The Arctic region has warmed more than twice as fast as the global average — a phenomenon known as Arctic amplification. The rapid Arctic warming has contributed to dramatic melting of Arctic sea ice and spring snow cover, at a pace greater than that simulated by climate models. These profound changes to the Arctic system have coincided with a period of ostensibly more frequent extreme weather events across the Northern Hemisphere mid-latitudes, including severe winters. The possibility of a link between Arctic change and mid-latitude weather has spurred research activities that reveal three potential dynamical pathways linking Arctic amplification to mid-latitude weather: changes in storm tracks, the jet stream, and planetary waves and their associated energy propagation. Through changes in these key atmospheric features, it is possible, in principle, for sea ice and snow cover to jointly influence mid-latitude weather. However, because of incomplete knowledge of how high-latitude climate change influences these phenomena, combined with sparse and short data records, and imperfect models, large uncertainties regarding the magnitude of such an influence remain. We conclude that improved process understanding, sustained and additional Arctic observations, and better coordinated modelling studies will be needed to advance our understanding of the influences on mid-latitude weather and extreme events.

Mechanisms that can potentially link fast warming in the Arctic region and extreme winter weather in the northern mid-latitudes are identified. However, how large the influence of Arctic ice and snow decline is on mid-latitude winter weather remains highly uncertain.

Judah Cohen and co-authors reviewed the literature on potential links between the amplified warming in the Arctic region and extreme weather events, and identified potential pathways of influence. Specifically, they suggest that a weaker temperature gradient between the Arctic and mid-latitudes could lead to changes in key features of the northern hemisphere atmosphere, such as the jet stream and the storm track. A weaker gradient could also alter the ways in which energy is transported by large-scale atmospheric waves. These changes, in turn, have the potential to influence the occurrence of mid-latitude weather extremes like the persistent cold conditions that hit the United States during winter 2013/14. However, the authors caution that better models and observations are required to quantify the strength of this influence.

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Last year’s severe winter brought into focus the debate of whether a warming Arctic is causing more extreme weather in the mid-latitudes especially more severe winters or not.  On one side scientists argue that a warming Arctic is definitely causing changes to the weather patterns in the mid-latitudes that favors increased extreme weather and on the other side there scientists that say the Arctic is not influencing mid-latitude weather and any observed changes are simply due to natural variability.

This debate has resulted in much confusion for the public.  This paper presents both sides of the argument.  It tries to explain how changes in the Arctic, in particular melting sea ice can influence mid-latitude weather.  In the paper we have grouped all the different studies on how melting sea ice and Arctic amplification can influence mid-latitude weather into three different pathways, changes in: storm tracks, the jet stream and planetary waves.

Though the opinion of the co-authors varied and were from both ends of the spectrum on this issue, I feel that the paper does agree that it is plausible that changes in the Arctic can influence mid-latitude weather.  And if this influence is detectable, then it is likely to be contributing to more severe winter weather relative to other extreme events (heat waves, flooding, drought).