Temperatures in the UK and Europe have been unseasonably cold recently. While not unprecedented – the UK has had the coldest March since 1962 – we simply aren’t accustomed to anything like these temperatures especially as March 2012 was the third warmest on record only outshone by 1938 and 1957. So why is it so cold at the moment?
For the answer, we need to look east, towards the vast plains of Russia.
Currently there is an intense area of high pressure over much of Europe, extending from Siberia in the east to the UK in the west.
This high pressure means clear, cloud-free days and, crucially, cloud-free nights. In the summer this same set up brought a heatwave to much of eastern Europe. But when it happens at this time of year, a heatwave could not be further from the truth.
The intensity of the high pressure means that air from aloft is being pushed downwards.
As air descends, it dries out. This results in little or no cloud. By night, cloud acts as a blanket, stopping heat that is in the ground radiating away into the sky.
So at the moment, we have short days, low heating of the ground, long nights and nothing to stop the heat from the ground escaping.
If these conditions last for a long time, it just gets colder and colder. That is where we are at the moment – the intensity of the high means no cloud, no cloud means colder and colder temperatures.
What normally makes the UK milder than other countries on the same latitude is the influence of the jet stream – a strong flowing ribbon of air that flows around our planet high up in the atmosphere, at around the level of the tropopause.
There has been strong evidence of accelerating Arctic sea ice loss recently which would lead to unusual weather patterns and effects on the jet stream. The recent cold snap in the UK would be consistent with the jet stream being blocked by the effects of melting Arctic sea ice.
Also remember that unusually cold conditions in one country do not indicate global trends especially with recent record temperatures in Australia and the US, plus concerns in European Ski resorts about increasing average temperatures and reducing snowfall. Weather isn’t climate!
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