Cold Snap in the United States and Canada

[BenForeback]

I have been following current news of the extreme cold snap in the northern United States and Canada. The temperature in Chicago is -27 C with “wind chill” of -40. Wind chills in parts of Manitoba are -55 C! This weather system has already broken many 50+ year records.

Climate change deniers will of course say that this is an “obvious” sign that the climate is not warming. Our counter-argument is that average & median temperatures are still increasing in the long-term. However, to those people, this is not necessarily a convincing argument related to the current situation.

Other than showing trends in global averages and some global climate models (which, to some, may not be that convincing either), how can we present a convincing argument that this current cold spell is only an isolated event and is not overall representative of the large-scale climate system?

[jouni.raisanen (Jouni Räisänen)]

Climate is the statistics of weather. Therefore, to decide whether the cold weather in this winter is an isolated event or whether it is actually representative of the current climate, we should in principle relive winter 2019 a large number of times (say 100 or even 1000) and count the number of cases in which such cold weather occurs. This is, of course, impossible.

However, when we take a wider view, observations show that extremely cold temperatures have become less common and extremely warm temperatures more common (e.g., https://www.ipcc.ch/site/assets/uploads/2017/09/WG1AR5_Chapter02_FINAL.pdf Section 2.6.1; https://link.springer.com/article/10.1007/s10584-015-1325-2; https://www.pnas.org/content/113/49/13977). This is as expected in a warming world.

In principle, climate change could lead to an increase in cold extremes in some locations, due to changes in atmospheric circulation. There is some evidence that this might be currently happening in central-eastern Eurasia due to the rapid decrease in Arctic Ocean ice cover (https://www.nature.com/articles/s41558-018-0379-3; https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-18-0234.1). But this is an exception. The general rule is that periods of extreme cold today occur despite of climate change rather than as a result of climate change.