My last blog-piece sparked off a twitter debate between Zoe Williams of the Guardian and one of the brigade of chicken headed deniers (See recent speech by Prince Charles). Richard Snape kindly recorded the conversation on this storify, and then went on to write a return blog-piece of his own. Thank you Richard, it’s very helpful and perhaps treats my piece with more gravitas than it deserved. The following is really a response so you’ll need to read it to make much sense of this post.
Importantly, mine is not a statistical analysis. The trouble is there aren't really any data to analyse. Rainfall records only go back ~250 years and I just made the wild assertion that this is the wettest such period since the Neolithic. That may or may not be true and probably we’ll never know.
It’s good not to cherry pick the data and I've not defined what period or events I'm talking about. Southern England December 2013, January 2014, into February 2014 and still counting, will do for time and space, rainfall, depression intensity and frequency, wind-speed, temperature, the whole gamut of weather will do for the 'event'. Sadly, we don't have the data set for all that lot going back to the Neolithic!
So is it 5-sigma? Well, frankly, I can't be certain; depending on where one draws the boundaries, it might be. Or not! You're quite right, Richard, about 'generic'. I'm wielding a broad brush. So never mind the data, your three points of 'implied argument' are spot on:
1. If the observation is very unlikely, then the distribution must have changed.
2. The distribution changing implies climate change (and often the anthropogenic forcing element thereof).
3. If the climate is changing - that cannot be coped with using Business-as-usual methods.
I love Nick Taleb; if you haven't yet, read Black Swan. Expect the unexpected.
But Richard, you say "climate science appears to indicate that warming would increase the amount of water that can be carried in the atmosphere". I’d put it more strongly. We know that global warming leads to more rainfall, (in as much as we know that apples fall downwards). And we’re not just dealing with Somerset. It’s reached Berkshire so must be important now. The bigger the unusual event is the more unusual it is, but of course there I go, cherry-picking boundaries.
“I think that Climate Change probably is happening." Good. But the IPCC put that more strongly. They use the word 'unequivocal' with reference not just to climate change but to the assertion that climate change is largely being caused by man-made greenhouse gas emissions. I agree with the IPCC position in this regard.
"Fundamentally, the rarity or otherwise of individual weather observations cannot, in my opinion, provide conclusive evidence for or against climate change." Very true, but the thing is, we've done and dusted that debate. We know, like we know that apples fall downwards, that our greenhouse gas emissions are causing global warming, which is, in turn, causing climate change (see my earlier piece on these phrases). There are plenty of details to research and argue about, which is what climate scientists do, (we're not quite sure which daisy the apple will roll onto) but all the scientists working in the field accept the basics. There is consensus. My political purpose is to get folks to realise this.
It's really very difficult for climate scientists to communicate what they really believe. Everyone, at least in public, has to be very careful, trying to please their employers and not risk their careers. (Be particularly wary of what some meteorologists say. Weathermen are not always climate scientists, failing to see the wood for the trees.)
One of the trickier areas is with the global climate computer models. The numerical models are largely built on the underlying assumption that the climate is stable and they do not sufficiently account for thresholds and tipping points. But don't be tempted to think that therefore the models are rubbish. That would be ignoring the vital rider that the probability space of error is all on the bad side. The models underestimate the likelihood of catastrophic change. If you are not frightened of serious mathematics you might like to dig into the work of Lenny Smith at the Grantham Research Institute on Climate Change and the Environment at the London School of Economics.
This diagram is for the comment below:
This diagram is for the comment below: