Do cold winters have an Arctic cause?

12 augustus 2019

Climate change leads to a warming Arctic and the decline of sea ice in the winter. The decrease in sea ice is sometimes linked to the occurrence of extreme winter cold at moderate latitudes. In a new study in the journal Nature Climate Change, researchers from the KNMI and the University of Exeter conclude that a decrease in sea ice does not cause the cold waves: fluctuations in the atmospheric circulation simultaneously cause both a decrease in sea ice and cold waves at mid-latitudes.

Recent studies into the relationship between the decrease in the sea ice in the Arctic and ice-cold winters in the moderate latitudes (for example the “Polar Vortex” cold waves in North America) seem to suggest that such a connection does indeed exist. However, the mechanisms behind this relationship have remained unclear so far, mainly due to the chaotic nature of the climate system.

This has changed with the publication of a recent article in Nature Climate Change, with Karin van der Wiel (KNMI) and Richard Bintanja (KNMI and RUG honorary professor) as co-authors. This article uses for the first time a very extensive set of climate data produced by two detailed climate models (including the KNMI climate model EC-Earth). The large amount of climate data enabled the authors to make statistical connections that were previously hidden in the noise of the climate system.

Analysis of the model data shows that relatively cold winters and Arctic sea ice decline occur at the same time, but that one does not cause the other. Both changes appear to be the result of a completely different mechanism, namely large-scale anomalies in atmospheric circulation. An important supportive finding of this study is that both climate models come to exactly the same conclusion. Also, a simulation with sea ice decrease imposed does not lead to cold winters at all.

The findings in this article show that a further decrease in Arctic sea ice in the (near) future will most likely not lead to more (and intense) wintry cold waves, because episodes with little Arctic sea ice are the result of unusual atmospheric circulation patterns, and not the cause.

A figure showing temperature and circulation for reduced sea ice
Top: temperature (colours, ०C) and atmospheric circulation (contours, hPa) associated with reduced sea ice in the Chukchi-Bering Sea. Middle (bottom): same, but for winters where sea ice (atmosphere) influences the atmosphere (sea ice)
Sea ice as in a world with 2 ०C global warming
Effect of reduced sea ice (left) on temperature (colours, ०C) and atmospheric circulation (contours, hPa) tested in an experiment with climate model HadGEM2-ES. Sea ice as in a world with 2 ०C global warming, all other conditions were kept constant.

Read more: Minimal influence of reduced Arctic sea ice on coincident cold winters in mid-latitudes