Today parts of Britain are colder than the North Pole. With spring tantalisingly close, the country is in the midst of a spell of bitingly cold weather. Up to eight inches of snow will hit eastern England by tomorrow.
Temperatures dropped to -9.2°C on Sunday, while the wind chill factor will make temperatures feel as cold as -15°C; so cold that it will cause power cuts and hit mobile phone networks. Commuters have been urged to get home by 6pm as the country faces travel chaos.
This icy weather is the result of a phenomenon called a “sudden stratospheric warming”. The stratosphere is the second major layer of the Earth’s atmosphere. It starts around six to eight miles above the surface and ends at 31 miles. Most of our weather comes not from the stratosphere, but from the troposphere below.
During the winter, a blob of extremely cold air spins clockwise in the stratosphere above the Arctic. It is particularly cold due to the total lack of sunlight hitting the Arctic at this time.
If the cold blob starts to spin slower, the air will rush back inwards. Think what happens when you are stirring a cup of tea very fast, and then stop. As it slows down, this air sinks through the atmosphere, becomes warmer, and then even starts to spin the opposite way.
Britain usually experiences westerly winds. This means they come from the west, not that they head towards the west. This is because of the northern hemisphere’s jet stream, which brings warm air across the Atlantic, and explains why the UK is much warmer than its latitude would suggest.
But a sudden stratospheric warming reverses this jet stream, and means that Britain’s weather starts coming from the east – meaning the freezing mass of Siberia. So while the west of the British Isles usually sees the most extreme weather, this time the eastern part of England that has born the brunt of this cold snap.
Scientists predicted that such events would become rarer due to climate change. But in fact the opposite has happened. Is this big freeze a purely natural event? In fact, many scientists are concerned this is a prelude to more extreme and less predictable weather. In the past couple of weeks, there has been a heatwave in the sunless Arctic even though the northern polar region has not had any sunlight since October. At times it has been warmer than London, Paris or New York. Veteran climatologists have been shocked by the recent temperature spike.
Instead of the gradual year-by-year rise that they were expecting, there has been jolt upwards that experts have described as “crazy”, “weird”, “shocking” and “worrying”.
From 17 to 25 February, there were 10 consecutive days where temperatures were above freezing for at least part of the day at the world’s most northerly land weather station – Cape Morris Jesup at the northern tip of Greenland. In total, the monitoring station has recorded 61 hours above 0C. According to Robert Rohde, lead scientist of the Berkeley Earth monitoring organisation, that is more time above freezing than the combined total of January through April for all previously observed years since the station opened in 1981. Plotted on a graph, this is so far outside of the historical range that Michael Mann, director of the Earth System Science Center at Pennsylvania State University, said the numbers represent “an anomaly of anomalies.”
We could think this is a one-off freak event because in climate terms, a few weeks is not nearly long enough to determine whether a new trend is emerging; Buy some scientists believe this could be an extreme case of natural variation. Temperatures fluctuate wildly at the north pole, though it is not normally as warm, as often or for so long.
However there is another theory about what is happening that could have much wider implications. The biggest concern is that this might indicate a weakening or collapse of the polar vortex, the circle of strong winds, including the jet stream, around the Arctic that act as a buffer or insulation, keeping the cold air mass in and the warm out.
The polar vortex gets its strength from the difference in temperature between the normally freezing Arctic and warmer more southerly mid-latitudes. But climate change is reducing the gap because the north pole is warming much faster than the global average.
Any weakening would accelerate ice melt and add to instability and uncertainty. It could also trigger the release of methane – a very strong greenhouse gas – trapped in the tundra. In December, the US National Oceanic and Atmospheric Administration warned Arctic sea ice was declining at the fastest rate in at least 1,500 years with an impact that would be felt far outside the region and affect the lives of every single American. One of the research team, Jeremy Mathis, compared the Arctic to the planet’s refrigerator.
“But the door to that refrigerator has been left open,” he said. “And the cold is spilling out, cascading throughout the northern hemisphere.”
Don’t jump to any rash conclusions, reply others. Records of extreme weather were patchy up until a few decades ago, and so we have surprisingly little data to analyse. Britain has seen far more extreme winters in centuries past. And the incorrect predictions prove one thing: no-one really knows what’s going on.
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