There is a ghastly sense of déjà vu about this summer, uncannily like last summer’s washout. The Atlantic has bombarded us with intense depressions that dropped some vicious downbursts of rain, and with the ground already wet, that rainwater has run off into flash floods, with more bad weather expected this weekend.

The culprit to blame is the jet stream. This river of high altitude wind snakes around the globe and steers Atlantic depressions towards Britain. Usually in the summer we would expect the jet stream to push off farther north, taking its wet and windy weather with it. But for the past few weeks it has clung to Britain, delivering the sort of storms you might expect in the winter. All of which is alarmingly reminiscent of last summer.

This behaviour of the jet stream could be thanks to the Pacific Ocean. For the past year or so, the tropical seas of the Pacific have turned unusually cool, a phenomenon called La Niña, and research at the Met Office’s Hadley Centre shows that La Niña can knock the jet stream off course in the summer, leaving foul weather over Britain. Even though the present episode of La Niña is now dying out, its influence lingers on and, sadly, means that the rest of the summer looks likely to continue the same unsettled weather pattern, just as the Met Office long-range forecast predicted.

Has any of this to do with global warming? No, not really. Summers in the future are expected to be hotter and drier, so that this summer and last year’s look like aberrations in the big climate picture.

However, climate change is expected to bring more intense rains and set off more of the sort of flash floods we are seeing now. And another interesting sign of the underlying change in climate is how temperatures so far this summer are bang on average. Compare this with bad summers of long ago, which were invariably cold as well as wet.