Usefully Useless

Think back to June 2007, when Britain flooded pretty much top to bottom. That has the same underlying cause as the big freeze of 2009-2010. What cause would that be? Global warming.

Surely I have to be making some kind of bad joke?

Absolutely not. Let me explain.

Britain’s climate is controlled by the jet stream, in the winter it hovers over Britain, deflecting air masses which would otherwise be coming down from the Arctic, the jet stream’s moist but not so cold air from the North Atlantic (warmed by the Gulf Stream). This keeps us much warmer than our latitude would suggest, after all, we are as far north as Moscow, Edmonton and Minsk and further north than Winnipeg.

(Note: This is why usually in winter when we have snow, it’s when easterly or south easterly winds bring up air masses from the continent and it’s the source of the phrase ‘it’s too cold for snow’, since when it really gets cold in Britain, it’s usually a stationary winter anticyclone)

However, the jet stream never came north this winter, it remained over the Mediterranean, giving Spain some terrible floods in December 2009. Without the jet stream protecting us, the northerly winds from the Arctic could freely blow south over Britain, giving us the sort of weather our northerly latitude would otherwise consider to be perfectly normal.

Why would such a thing happen?

The jet stream changes course as it cools from summer to winter, but the jet stream was too warm to head north, so it remained in its summer position. Back in 2007 a similar thing happened, the jet stream didn’t cool down enough in the winter (2006-2007 was an exceptionally mild winter) to head south for the summer, so remained over us in its winter position and dumped off a ton of rain from the North Atlantic which gave Spain a hell of a bad drought and was meant to be distributed across the Mediterranean as far as Egypt, instead we got it all.

The same problem both times: The jet stream was too warm.