This time last week you’d have been forgiven for thinking spring was just around the corner. But now the UK has been plunged into freezing cold temperatures and parts of the country are under snow, thanks to a blast of cold air forecasters are calling the “beast from the east.” The Met Office says in some areas it’ll be the coldest spell we’ve had for several years. Does it have anything to do with climate change?
It turns out our current weather can be blamed on a meteorological event called “sudden stratospheric warming.” It all starts with a pool of cold air about thirty kilometres above the North Pole. A specific set of meteorological circumstances lead to the air being compressed, which in turn makes it up to 50 degrees warmer in a matter of days. When that happens, it sets off a chain of events that lead more often than not to wintry conditions for all of us on the ground.
What is sudden stratospheric warming?Usually the UK’s weather comes in from the west and we get relatively mild air from the Atlantic. But after sudden stratospheric warming happens, the newly warm air above the North Pole disturbs the jet stream, blocking the mild Atlantic weather from reaching us and allowing cold air in from eastern Europe. This cold air gets trapped and builds up, eventually coming down to ground level. “The jet stream has weakened and actually buckled,” says Met Office spokesperson Oli Claydon.
That’s how this particular cold snap came to be. But you’re probably aware that extreme weather events are due to increase in frequency because of climate change.
Just last week researchers from Newcastle University published a paper analysing how floods, droughts and heatwaves are all set to become more common in European cities in the years ahead.
As well as looking to the future, scientists are now beginning to figure out which past extreme weather events can be blamed in some way to human-induced climate change.
Using the emerging science of probabilistic event attribution, scientists at the University of Oxford have shown that Storm Desmond in 2015 and the floods in the southeast in 2014 were most likely made worse because of human activity.
Another study has linked human activity to the record temperatures seen in central England in 2014.
Is this cold snap the same?So we can draw a line between some events and human-induced climate change. Can we do it for this cold snap?
It’s tempting to attribute any extreme weather thrown our way to our changing climate, but it’s not as simple as that. And it’s difficult for scientists to say in the moment whether any particular weather was helped along by our changing climate, or if it would have happened anyway.
Dr Karsten Haustein works on the World Weather Attribution project at Oxford. He and his colleagues are working on as near to real-time event attribution as possible, and they analysed the recent cold weather in December and January in the US.
They found that rather than becoming more frequent, those cold spells were becoming rarer, and not as cold as they used to be.
However...But the specific cause of the UK’s current freezing temperatures could actually become more likely thanks to climate change.
There’s an idea, currently under debate, that declining arctic sea ice could have the knock on effect of making the sudden stratospheric warming events more frequent.
“The idea is that there’s a tendency to more blocking, and if we block the circulation of winds, so westerly winds are weakened, we’d get more cold spells,” says Haustein.
Right now, though, there’s not enough evidence to call it. “The last ten years would suggest that [it is the case], but that’s way too short to say whether or not this is real.”
Either way, Haustein is sure that whatever cold snaps we do get are getting warmer.
“Extreme cold is certainly on the retreat, no matter whether we get cold spells more frequently or not,” he says. “Perhaps now we’ll see -5 or -8 degrees when we look at the forecast, and in the past it might have been -10 or -12 degrees.”