Thursday, January 23, 2020

Perspectives on Linkages Between Arctic Warming and Severe Winter Weather

A hot climate topic in recent years has been the possible linkage between a warming arctic and midlatitude weather extremes, including severe winter weather.  An example of the types of headlines you've probably seen before is provided below from The Guardian

Source: The Guardian
This is a subject that has caused me a good deal of indigestion and that I've largely avoided in this blog.  This is because most of the evidence for this linkage has been based on observational studies, whereas model based studies have obtained differing results.  

A new review article is now out in Nature Climate Change discussing the differing perspectives obtained form observational and modeling studies.  The paper is led by Judah Cohen and involbes a large number of authors including HongPing Gu and Simon Wang of Utah State University and the Utah Climate Center.  

Source: Nature Climate Change
Sadly, the paper is paywalled, but the National Science Foundation Public Affairs Office has issued a plain-language summary that describes the issues at play.  It is available at, although I've included a screenshot below if you want to take a quick look (click to blow up).

Source: NSF
To summarize the issues at play, the Arctic has been warming twice as fast as the global average, a trend that has long been anticipated and is known as Arctic Amplification.  The causes of this amplification are multifaceted and complex.  Feedbacks related to a loss of Arctic ice are most commonly cited by popular media, but as summarized below, there are others.  

Source: Cohen et al. (2020)
In turn, it has been hypothesized that Arctic Amplification may be affecting midlatitude weather.  For example, the decline of Arctic sea ice in the fall can intensity Arctic storm systems, which could potentially lead to weakening of the polar vortex.  A weaker jet stream might also be expected due to the weakened temperature gradient between the arctic and the lower latitudes.  These are simple generalizations and ultimately linkages between the Arctic and the midlatitude depend on several factors and are sensitive to regional changes in sea-ice loss and other subtleties.  

What one would hope is that observational and modeling evidence would like up and agree, but at present, they do not.  Observational studies reveal relationships and suggest linkages.  The period that can be investigated observationally is, however, relatively brief given the amount of variability in the atmosphere.  Modeling studies allow us to simulate much longer periods of time and conduct experiments in which we can hold one thing constant but change another, but are limited by model imperfections.  

At present, observational studies have identified some relationships between Arctic Amplification and midlatitude severe winter weather.  Recent modeling studies suggest, however, that the atmospheric response to recent Arctic sea ice trends is negligible.  As noted by Coehen et al. (2020), "A number of large ensemble modeling studies have come to the same conclusion — that is, there is little modeling evidence of an atmospheric response to the pan-Arctic sea ice trend."  

This is how science works.  Hypotheses are put forth and tested, often using multiple approaches.  Discrepancies are then investigated, methods refined, and hypotheses revised and retested.

I don't know how this process will conclude.  It is possible that we will learn that recent trends reflected variability and it was coincidental that there appeared to be a linkage between arctic warming and midlatitude severe winter weather.  It is possible that deficiencies in the modeling system or experimental designs will be identified.  Finally, it is possible that we're just not looking at the problem properly and that new theory and better theory will be developed.  Eventually we will figure this all out.  

1 comment:

  1. I find it very interesting that the US area affected by the cold polar vortex conditions is the same area buried under ice-sheets in the last glaciation.
    Another coincidence?