‘Case against climate change discredited by study’ shrieked the Independent yesterday. That must be one hell of a study. Except that it isn’t:
A difference in the way British and American ships measured the temperature of the ocean during the 1940s may explain why the world appeared to undergo a period of sudden cooling immediately after the Second World War.
Scientists believe they can now explain an anomaly in the global temperature record for the twentieth century, which has been used by climate change sceptics to undermine the link between rising temperatures and increases in atmospheric carbon dioxide.
Not only does the study (published this week in Nature) not claim to discredit what the Independent‘s headline claims it discredits, but it doesn’t even discredit what the scientists behind the study claim it discredits. Moreover, what the scientists claim their work does discredit was, according to prominent Environmentalists, discredited years ago. And finally, what everybody seems to be trying to discredit isn’t even something that sceptics seem to be crediting in the first place.
Yes, sceptics are concerned about the post-war temperature slump, but not because of the sudden steep drop around 1945; it is the downward trend in temperatures between about 1945 and 1975 that they suggest needs explaining (which is actually longer than the upward trend between 1975 and 1998, just so you know), given that greenhouse gas emissions were rising throughout that period.
And as the graph used by the Independent to bolster its case (supplied by CRU, apparently) demonstrates, the Nature study does absolutely nothing to address that concern:
In fact, the most striking thing about the graph is that, once the sampling errors identified by the study have been taken into account, the period of warming in the latter half of the twentieth century was shorter than previously thought, and that the ’45-’75 temperature slump is more pronounced.
According to Phil Jones, a co-author of the paper, the study
lends support to the idea that a period of global cooling occurred later during the mid-twentieth century as a result of sulphate aerosols being released during the 1950s with the rise of industrial output. These sulphates tended to cut sunlight, counteracting global warming caused by rising carbon dioxide.
“This finding supports the sulphates argument, because it was bit hard to explain how they could cause the period of cooling from 1945, when industrial production was still relatively low,” Professor Jones said.
That might be so. But the aerosols issue is supposed to have been done and dusted long ago. One of the central criticisms aimed at the infamous Great Global Warming Swindle, for example, is precisely that it failed to entertain the idea that the post-1940 decline in global temperatures was the result of increases in sulphurous emissions that masked the forcing effect of rising atmospheric CO2. George Monbiot described the omission as ‘straightforward scientific dishonesty‘. After all, he said, that ‘temperatures declined after the Second World War as a result of sulphate pollution from heavy industry, causing global dimming…is well-known to all climate scientists.’ And as we have reported before, this was also one of the main points raised by the Royal Society’s Bob Ward and 36 scientific experts in their open letter to Swindle producer Martin Durkin.
And yet, as we’ve reported elsewhere, other experts in the field just don’t agree. UC San Diego atmospheric physicist Veerabhadran Ramanathan, for example, told us that the empirical evidence for the sulphate masking of warming is ‘pretty flimsy’. We do not doubt that the Nature study is an important contribution to the field. (Although it’s interesting that Steve McIntyre seems to have produced a similar analysis more than a year ago.) What we do doubt is that the headlines, soundbites, and wild interpretations from newspapers and scientists alike bear much relevance to what is a dry, technical, scientific study, which, while increasing our ability to understand and predict climate trends, says little in itself about the truth or otherwise of global warming.
Corrections for this measurement switch have not yet been applied to produce a new graph of 20th Century temperatures – that work is ongoing at the UK Met Office – but as the land temperature record shows a flattening of the upwards trend from the 1940s to the 1970s, clearly something did change around the 1940s to ameliorate the warming.
“It perhaps suggests that the role of sulphate aerosols, that cooling effect, was less powerful than we thought,” said Mike Hulme from the University of East Anglia (UEA), who was not involved in the study.
George Monbiot and the Royal Society are just plain wrong – the science is plainly not ‘settled’. And so is Steve Connor, the author of the Independent article. As he wrote last year in response to the Swindle:
The programme failed to point out that scientists had now explained the period of “global cooling” between 1940 and 1970. It was caused by industrial emissions of sulphate pollutants, which tend to reflect sunlight. Subsequent clean-air laws have cleared up some of this pollution, revealing the true scale of global warming – a point that the film failed to mention.
‘Scientists’ have ‘explained’ nothing of the sort. As this case shows, the science is not settled. Indeed science is never settled. It is constantly re-evaluating what it understands about absolutely everything. And that’s especially crucial to bear in mind when the science in question has been bestowed with the kind of political significance that climate science has. To claim otherwise is to do a disservice to both science and politics. It reduces science to a flimsy fig leaf used simply to hide the embarrassing inadequacies of the latest political fad; and it reduces politics to an aimless exercise in number-crunching.