Global warming may be behind an increase in the frequency and intensity of cold spells

By Beatriz Monge-Sanz, University of Oxford

Global warming caused by increased concentrations of greenhouse gases is already affecting our lives. Scorching summers, more intense heatwaves, longer drought periods, more extended floods, and wilder wildfires are consequences linked to this warming.

One less obvious consequence of global warming is also getting growing attention from scientists: a potential increase in the intensity and frequency of winter cold snaps in the northern hemisphere.

Weather phenomena like the Beast from the East in winter 2018, the cold spell of Arctic air that reached as far South as Texas in February 2021, or the storm that left Madrid and Athens unusually covered in snow for days in early 2021 are becoming more common.

Some of the mechanisms that lead to their occurrence are strengthened by global warming. Key climate mechanisms, like exchanges of energy and air masses between different altitude ranges in the atmosphere, are evolving in ways expected to cause an increase in both the intensity and duration of cold snaps. These link to the behaviour of a region in the high atmosphere called the stratosphere.

Winter cold snaps have major societal impacts, from direct effects on health and loss of life, to effects on transport and infrastructure, surges in energy demand and damage to agricultural resources.

This winter, we have seen these effects over large parts of Europe and the US, with flight cancellations, airport closures, road queues and drivers trapped in extreme cold temperatures. There have also been sharp increases in energy demand to cope with indoor heating, an increase in cold-related hospital admissions and the activation of services needed to assist the most vulnerable.

We need to develop forecasting tools that can predict these events further in advance.

Polar vortex

Some of these cold snaps are linked to disruptions in a seasonal atmospheric phenomenon called the stratospheric polar vortex (SPV).

In the northern hemisphere, this vortex consists of masses of cold air centred over the north pole, surrounded by a jet of very strong westerly winds between 15-50km above ground.

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