Apr 012011
Surface temperatures measured by thermometers ...

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ON THURSDAY March 31st Richard Muller of Lawrence Berkeley Laboratory gave evidence to the energy and commerce committee of America’s House of Representatives on the surface temperature record. Without having yet bothered to check, Babbage can say with some certainty that this event will be much discussed in the blogosphere—as, oddly enough, it should be.

Here’s the short version of the reason why: a new and methodologically interesting study, carried out by people some of whom might have been expected to take a somewhat sceptical view on the issue, seems essentially to have confirmed the results of earlier work on the rate at which the earth’s temperature is rising. This makes suggestions that this rise is an artefact of bad measurement, or indeed a conspiracy of climatologists, even less credible than they were before.

Now here’s the much longer version.

There are two topics which, more than any other, can be guaranteed to set off arguments between those convinced of the reality and importance of humanity’s impact on the climate and those not so convinced. One revolves around the question of how reliable, if at all, statements about average global temperatures before about 1500 AD are. This is the so-called “hockey stick” debate. The amount of computer processing power and data storage capacity devoted to endless online discussions of the hockey stick— the subject featured in a great deal of the brouhaha over the “climategate” e-mails—must, by now, have the carbon footprint of a fair-sized Canadian city, which of course would worry one side of the argument not a whit.

The second touchy topic is the instrumental record of the world’s temperature over the past 100 years or so. This is a more genuinely interesting subject, for two reasons. First: Consider a person who looks at all the non-hockey-stick evidence and arguments for thinking people are changing the climate (we won’t rehearse them now, but here’s a relevant article from The Economist last year). Imagine this person then saying “you know, that radiation balance and basic physics and ocean heat content and all the rest of that stuff looks pretty conclusive—but because I can’t say for sure whether it was warmer in 1388 than it was in 1988 or the other way round I’m going to ignore it all.” This would probably not be a person you would take very seriously.

(It is because of this that the wiser sceptical voices in the hockey-stick debate do not claim that uncertainties over what, if anything, can reliably be said about mediaeval temperatures invalidate the scientific case for a strong and worrying human influence on climate. They say instead that there are a variety of statistical and other flaws in some of the reconstructions of mediaeval temperature, that some of the scientists responsible for some of these reconstructions have not behaved well, and that if that is typical of climate science then climate science in a whole is in a bad way. Thus the hockey stick becomes a sort of meta-, and indeed metastasising, argument.)

If, on the other hand, you imagine a person who has looked at all the other relevant material going on to say “You know, this is all very well—but there doesn’t seem to be any conclusive evidence that the world has actually been getting warmer in a significant or surprising way over the past decades,” you might well think hmm; if that’s the case then he has a point. Evidence that the world really is warming does seem pretty apposite to the whole issue. Being able to trust the records of what thermometers spread out over the world have actually measured and the procedures by which  those records are combined into a series of average global temperatures matter rather more than the hockey-stick.

Another reason is that mediaeval data (from tree rings and the like) at issue in the hockey stick debate are necessarily sparse and patchy, and coming up with really robust answers to all the relevant questions on the basis of them may well prove impossible. The data on which the contemporary surface temperature record is based, though, is rich. There are a great many temperature records in archives around the world. If you can choose records that are demonstrably reliable and combine them in an appropriate way, you should be able to get a pretty solid answer. This thus seems like an argument that could conceivably end in agreement on an important issue.

Indeed, most climate scientists would say that it already has. There are three different combinations of instrumental temperature records that seek to show average surface temperatures back to 1900 or earlier. Two are American, with one produced by the National Oceanic and Atmospheric Administration (NOAA) and one by NASA; the other one is British, with data from the Met Office and the University of East Anglia’s Climatic Research Unit (which was the epicentre of climategate). They used many of the same raw data, but the ways in which they adjust them to remove presumed artefacts and then combine them differ. Yet they come up with very similar answers, and when they publish their figures with error estimates they come within each others’ margins of error. The fact that three different groups agree in this way would normally seem to justify relying on the result.

But there are many ways in which climate science is not normal, one of which is that it matters a great deal with respect to some very expensive policy decisions. Various criticisms of the methodology and probity of the temperature records have been made, though much more often in the blogosphere than in the scientific literature. Erring on the side of extra caution is not a bad idea, and various efforts are underway to develop, corroborate and better to underpin the work on temperature records that has been done to date. One such effort is the Berkeley Earth Surface Temperature programme, which Dr Muller heads.

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