As I write this, a vast swathe of northern Russia swelters in a heatwave. Not just in a relative sense, either – most people would find it hot! Daily maximum temperatures are regularly ranging from the mid-20s to low-30s °C. It’s part of a run of predominantly well above normal temperatures that’s been ongoing for several months now.
Triple Digit Temperatures Within the Arctic
During an event like this, high temperature records tend to be broken. Case in point – the town of Verkhoyansk, usually among the coldest settlements on Earth in winter, reached a mind-boggling 38°C on 20th June 2020. That’s just over 100°F – a benchmark never before recorded so far north by reliable measurements.
We’re talking about a place about 4,660 km northeast of Moscow, just 363 km from the Arctic Ocean, reaching a temperature a mere 0.7°C shy of the UK national record! In fact, this location is just inside the Arctic Circle*.
All this extraordinary heat begs the question: how and why is it happening – is it climate change?
Polar Preconditioning: Extremely Mild Winter
Last winter was no ordinary affair for the northern hemisphere’s northern half.
A phenomenon known as the polar vortex was unusually strong for most of the time late December on. Sometimes it hit record-breaking intensity.
This stirred the atmosphere on a vast scale, in an anticlockwise direction. This meant that storm systems developing over the oceans (wet and windy weather) moved eastward unusually fast. Their movement also tended to be very ‘flat’, which is to say, they didn’t move north or southward much – mostly eastward. Similarly, areas of high pressure across locations such as the southern half of Europe rarely extended much to the north.
Such a weather ‘regime’ has the effect of ‘bottling up’ cold air over the Arctic Ocean. Meanwhile, the rampaging westerlies transport an abundance of mild air across the continents from over the oceans.
This is especially true for Europe and Asia. Reason being, the north-eastern North Atlantic is warmed by an ocean current known as the Gulf Stream. Waters just north of the UK can be 3-6°C above zero even in late winter.
With an exceptionally strong polar vortex, this effect reaches thousands of miles eastward. As you can see below, the imprint of this on Jan-Apr 2020 mean temperatures was profound.
The anomalies generally increase as you look further east, for it becomes increasingly rare for the balmy westerlies to predominate so far from the North Atlantic.
Shortfalls of Snow
How this relates to the exceptional May-June warmth is not as simple as you may think.
You see, most of the northern half of Russia was still mainly below freezing even with these huge positive temperature anomalies. Snowfall was close to average in that region.
So, what gives? To see that, we need to look further south and west. Most southern parts of Russia and the majority of Europe saw a deficit of snow cover. In many places, a big one.
Without a white cover to reflect sunlight and facilitate cold air pooling, the strengthening spring season sunshine was able to raise temperatures a lot faster than usual in those areas. Extensions of that anomalous warmth (in response to weather systems) then led to unusually rapid loss of snow cover further north. You can see this sequence in the maps below, adapted from the Rutgers Snow Lab website.
See how the snow deficits shifted northward from one month to the next, with those of May 2020 matching well to where the exceptional heat has been observed in recent weeks.
Early loss of snow cover in turn facilitated higher temperatures, so reinforcing this process of aggressive snow melt (a positive feedback). This also meant less cold air available nearby to help bring an end to anomalously high temperatures further south. So, the heat just kept on building overall across a vast area.
In the past few weeks, this heat has been journeying back and forth between different parts of Russia. Sometimes, some has been exported westward to Europe or northward across the Arctic Ocean (leading to the fastest sea ice loss on record in some peripheral seas). So far, though, there’s not been enough of that to outweigh the energy input from the sun – the heat goes on.
It’ll be more than a month before the days have shortened enough that the heat will start to subside whenever left to its own devices. Until then, the wildlife, permafrost and nearby sea ice are all at the mercy of the weather patterns.
At the time of writing, weather forecast models suggest no respite for a large area of Russia during the next week or so. The far-west is a notable exception. I dread to think what this is doing to the permafrost in Siberia, for example. There are dire implications of strong permafrost melt, including extensive methane release.
Global Ensemble Forecasting System 20-member mean predictions for 2 m temperature anomalies across two periods of 5 days: 26th June to 1st July (left) then 1st July to 6th July (right). Source: https://www.tropicaltidbits.com/
What About Climate Change?
I’ve deliberately skirted around this aspect until now. Reason being, I want to emphasise that climate change overlays upon shorter-term variability such as the winter polar vortex intensity. It alone can’t explain what’s taken place in northern Russia so far this year.
It’s certainly an accomplice to the crime, though. There’s more heat available for a strong polar vortex to move around. There’s less cold air on tap to halt or even ‘undo’ snow cover losses following warmer spells of weather. It now takes an unusual persistence of cold-favouring weather patterns to prevent a faster than usual advance of snow cover loss.
I think this last point is well-illustrated by recent events in the Canadian Arctic Archipelago. Here, Jan-May was predominantly cooler than usual, resulting in above-normal snow cover. There’s still some left as I type this. Yet in the past week, a shift in weather patterns has led to unusually high temperatures there, which look to continue for at least another week. If not for the snow cover, this heat would be on par with what’s taking place in north-eastern Russia.
More Frequent Fast Snow Losses
As the climate continues to warm in the coming decades (based on model projections), fast losses of snow cover leading to exceptional ‘northern’ heatwaves are likely to occur increasingly often.
There will always be large variability between years, as snow cover varies in tandem with polar vortex strength – but will take less and less from the weather patterns to initiate a positive feedback of aggressive snow cover loss and temperature rise.
Associated with this will be an increased frequency of strong sea ice losses in the peripheral Arctic seas. Faster losses each melting season, which can in turn expose the central Arctic to stronger assault from melt-inducing weather. Overall loss of sea ice over the years can then facilitate even faster springtime warm-ups… and so the vicious cycle self-perpetuates. It will take a monumental intervention to break it.
James Peacock MSc
Head Meteorologist at MetSwift
* The Arctic Circle is a boundary marking the distance northward at which locations start to see at least one day with no visible sun in winter (polar night) and one with the sun never setting in summer (polar day). This does not include the UK, despite how often no visible sun seems to feature there in the winter (it’s still rising and setting, behind the clouds!).
Cover Photo by Unknown Author is licensed under CC BY-NC-ND