Every time the weather does something, somewhere, we break out into the same argument, about what it means for the climate change debate. Cold weather in the US, hurricanes in the Philippines, droughts and heatwaves in Australia, and, of course, drenching storms in Britain: is it caused by (or does it disprove) anthropogenic climate change?
I want, therefore, to make the obvious point: the world is a big place and the climate is a complicated system. At any time, somewhere in the world, somewhere will be experiencing “the worst X in 100 years” or “the longest Y since records began” or “the wettest Z since the Second World War”. That’s always going to be the case, and the fact that we happen to be the place that is experiencing it at the moment does not mean that we can extrapolate globally, any more than if I won the lottery I could say that everyone in Britain has just become a millionaire.
What’s interesting, then, is not whether any particular place is undergoing some spectacular climatic event, but whether those events are becoming more common in general, worldwide.
With hurricanes, and storms in general, that’s very hard to tell – they’re fairly rare events, so trends are hard to distinguish – but the answer is “very slowly if at all”. Last month the US National Oceanic and Atmospheric Administration’s Geophysical Fluid Dynamics Laboratory released a review of the literature, which found a very slow trend towards more storms – about five extra storms per century in the Atlantic.
It concluded that “It is premature to conclude that human activities – and particularly greenhouse gas emissions that cause global warming – have already had a detectable impact on Atlantic hurricane activity.” Similarly a 2010 World Meteorological Organisation study found only a very slow increase over centuries, and was unable to “conclusively identify anthropogenic signals” (ie human causation). Whatever else we’re doing to the climate, we can’t reliably say we’re making more storms.
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Unfortunately, we have a tendency to extrapolate from our own experience. That’s why people who’ve been mugged tend to think that crime is up, and people who have a bad time in hospital tend to think that the NHS is getting worse, and people who meet rude kids tend to think that the kids today have no respect. So the fact that Britain’s had a strange few years of weather makes people assume it’s global warming. But that’s no better than the Donald Trumps of this world who say “it’s snowing here SO MUCH FOR GLOBAL WARMING”. We need to look at global trends, and globally, there hasn’t been a significant increase in the number of storms.
This isn’t to say that global warming hasn’t had noticeable effects on extreme weather. Worldwide, heatwaves have become more common; a study in the journal Climatic Change found record-breaking monthly average temperatures are five times as frequent as they were in 1900 – and that almost certainly is caused by human activity. We can’t say that the Australian heatwave of recent weeks is caused by it, because that’s not how probability works, but we can say that global warming made it more likely.
But the storm that just battered Britain, and the others that hit us in December, are not part – as far as we can tell – of a wider trend. It’s just a storm.
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