Saturday, December 4th 2010, 4:21 PM EST
Climate change could bring Britain ever more extreme weather.
As a blanket of snow settles across the country, train services grind to a halt and roads become impassable, you could be forgiven for thinking that global warming seems more remote than ever. But yesterday, the World Meteorological Organisation announced that 2010 is almost certain to rank among the three warmest years since records began in 1850 – and it has long been accepted that one of the effects of climate change could be an increase in the frequency of harsher, Continental-style winters.
So which is it? Is it the vagaries of the elements that we should be cursing through our chattering teeth, or the carbon emissions from Chinese smokestacks?
Well, the most alarming way in which temperatures in Britain could fall significantly is through a decline in the warm Atlantic current that maintains our mild climate. Although our weather depends on turbulent events in the atmosphere, these are shaped – in the long term – by the oceans, whose currents transport vast amounts of heat around the planet. Ancient records show that if these slowed or stopped, temperatures could drop by up to 10C within decades.
Updated below with comments by Piers Corbyn
For six years, a team at Southampton University has been using instruments, strung across the Atlantic from the Bahamas to north Africa, to monitor the Atlantic Meridional Overturning Circulation. This is the massive system of currents, including the Gulf Stream, that carries a mind-boggling 1.3 petawatts of heat – that's 1,300,000,000,000,000 watts – northwards in its warm upper waters.
The Gulf Stream relies on the fact that as the water loses its heat in the north Atlantic, it cools, sinks and flows back to the south. The fear has been that, as the planet warms, melting Arctic ice will weaken these currents, plunging Europe into the cooler.
On this count, however, there is good news. According to Prof Mark Maslin, of University College London, there seems – at present – "to be no evidence of changes in the Atlantic circulation which could account for the last two harsh winters". There are, he says, shorter-term patterns in ocean circulation which have a major effect, and have been linked to the severe winters in the 1940s and 1960s. But again, that is probably not the case today.
So why is it so bone-chillingly cold? Well, Prof Maslin thinks the cause of the big freeze can be found in the atmosphere. As Ewen McCallum, the chief meteorologist at the Met Office, explains, this year and last have seen large areas of high pressure develop in the Atlantic, blocking the westerly winds and allowing chilly Arctic air to move south across Europe.
Winds from the east are always freezing – and at this time of year, the long nights cool the European land-mass more rapidly, meaning that the air remains bitterly cold when it reaches us. To make matters worse, the winds pick up moisture and heat as they cross the North Sea, which is dumped on us in the form of snow (explaining why coastal areas to the east have seen the heaviest falls).
But before we write off our current cold snap as the British weather playing its usual tricks, we still need to explain why the Arctic high pressure has strayed so far south. And here, says Prof Maslin, is the more likely, and more subtle, link with climate change. "For me," he says, "this shows that the climate is becoming more dynamic, and thus large shifts in the wind patterns are possible – in this case, sub-tropical air being trapped further south than usual."
In other words, we need to remember that while the average temperature is rising, climate change also delivers more extreme weather, from chills to heatwaves. Today, we're stocking up on snowshoes – but best to invest in some air-conditioning as well.
Roger Highfield is the Editor of 'New Scientist'