December 2010 the British weather delivered an early and spectacular cold blast to mark the start of the climate-change talks in Cancún, Mexico. Snow fell heavily in much of the country, and lightly over all of it; temperatures dropped to below -10°C. The chill might not presage another enduringly severe winter like that of 2009-10, but it has already brought a familiar crop of stories about traffic turmoil and closed schools. It might also add to Britain’s scepticism about climate change (already more widespread than in many other European countries).
It shouldn’t. While the beginning of 2010 is remembered by northern Europeans, Russians and inhabitants of America’s southern states as very cold, it was warm elsewhere, peculiarly so in Canada and Greenland. The average global temperature from January to March was the fourth highest on record. This is one of the reasons why 2010 as a whole seems likely to rank first or second in the list of average annual temperatures (depending on which bunch of climate scientists is doing the ranking).
Europe’s cold winters and the warmth of the planet as a whole might even be linked. There is some evidence that the summer heat stored in the newly ice-free seas north of Siberia may induce shifts in the atmosphere’s circulation, when the heat is given up to the air in subsequent autumns and winters. Those shifts might in turn encourage seasonal patterns in which the Arctic is warm and the continents below it cold, as in early 2010. Since the sea-ice area looks likely to go on shrinking, such a link, if indeed it exists, would probably mean more cold winters in Britain and much of Europe.
Other research suggests that warming may actually have alleviated recent freezes. A team of French climate scientists analysed last winter’s European weather day by day. For each day’s arrangements of high pressure, low pressure, wind speed and the like, they looked for similar days at similar times of year in records stretching back to 1948. In general, cold winter days in 2010 turned out to be less cold than equivalent days in earlier years had been.
Overall, judging by pressures and winds, 2009-10 should have been as cold as 1963, the coldest winter in the records analysed, with temperatures on average 4°C lower than normal. Instead it was the 13th coldest winter with an average temperature just 1.3°C below normal. Britons put out by the current bout of cold weather will get little satisfaction from the thought that it could have been worse. But it used to be.
So what is in store for the 2011 winter season, will we experience another cold snap that throws the country into disarray or will it be mild winter?