Behind the Science Does global warming diminish when measured accurately? Part 5
| 11 July 2009
One group of workers in the field of climate change has managed to make global warming appear worse than we originally thought. This group includes Michael Mann, Eric Steig, Caspar Ammann and Steven Rahmstorf. They are all also contributors to the Real Climate weblog, a compendium of global warming information that strongly supports the theory that humans are endangering the planet by emitting CO2 and warming the planet.
Starting in 1999, the gentlemen listed above and other contributors published a series of papers that questioned long-accepted reconstructions of past temperatures. They have recently published other papers implying that global warming is occurring in the Antarctic, and most recently, that recent temperatures have been climbing at or above estimates made as recently as two years ago.
What their work has in common (by that I only mean the papers that have generated controversy) is unconventional treatment of statistical analyses that produce unusual results which support their political position on global warming. They are accused of 'torturing the data until it confesses,' to borrow a phrase that has suddenly become popular (I think I read it first in a review of Ian Plimer's new book Heaven and Earth, but it may have been elsewhere).
Michael Mann and his fellow contributors are the creators of the infamous Hockey Stick Graph, which appeared on the cover of a 2001 IPCC report and several times inside. The paper that introduced the graph used multiple data sets about historical temperatures to show that our current global temperatures are the highest they have been for over a thousand years. In doing this, their data seemed to eliminate periods that have long been accepted as being warmer than today (the Medieval Warming Period, which lasted from the 10th to 14th centuries A.D.), and the Little Ice Age, which lasted from the 16th to the mid-19th centuries A.D.).
Here is what we formerly thought temperatures looked like over the past 11,000 years (Northern hemisphere temperatures measured in summer):
And here is what Mann et al presented to the world:
The impact of the Hockey Stick Graph was dramatic--it was used by Al Gore in the film An Inconvenient Truth and in countless other documents to show that temperatures were climbing dramatically and indeed had never been higher in historical times. It seemed to be the new smoking gun that proved global warming.
But you don't see the graph in new publications any more. In fact, the Hockey Stick chart seems to have disappeared. Critics found a gaping hole in his analysis techniques, and his use of one controversial set of proxy temperatures taken from bristlecone pines, which the creator of the dataset had specifically said shouldn't be used for temperature records. The controversy is documented on Wikipedia here. The critics' explanation is found here, and Mann and his fellow contributors to Real Climate defend themselves here. (If you detect a note of caution in my writing, it is because some at Real Climate have criticized me--and I don't want to give the impression that this is a response to their criticism.)
During the controversy, Mann was less than forthcoming in producing his source data, and a flurry of papers published just as the controversy reached its height seemed to support his position--until it turned out that many of the report writers were also contributors to Mann's work. This fueled the suspicions of skeptics about the whole affair being an exercise in propaganda. What also hurt sane discussion was a new and sudden campaign designed to blot out the Medieval Warming Period and Little Ice Age as either non-existent or more moderate and local fluctuations. The whole discussion was unedifying in the extreme, and has led to high levels of mistrust of this type of study and the communications strategy of those pushing global warming mitigation schemes.
The same basic story line is repeated more recently, not once, but twice. Mann's fellow contributor to Real Climate, Eric Steig, joined him in measuring temperature data in the Antarctic. Again, the initial publication was seized on as evidence that global warming had reached even the frozen wastes of Antarctica, and that things were worse that we had feared.
But again, most of the data was from the West Antarctic Peninsula, which juts into the warmer ocean currents south of Argentina, and which was known to be warming a century ago. There was not really adequate data from the other 95% of Antarctica, and the way Steig et al interpreted the data for the continent was compared by critics to spreading jam (from the small West Antarctic peninsula) across a piece of bread (the remaining 95% of Antarctica). And again, the paper is not really being put before the public eye any more.
Most recently, the Copenhagen Summit featured work by Steve Rahmstorf that seemed to show an uptick in temperatures that led to claims that temperatures were rising faster than had been believed. But again, upon publication, Rahmstorf's choices in analysis received immediate criticism, and claims that he had ignored IPCC procedures for computing the averages used in showing temperature trends.
The upshot is that a series of provocative claims about worsening climate situations are published and used in political documents, and are later found to have serious problems with how data is treated. How is the skeptical community supposed to react when this happens three times, coming from people who form part of the contributing community at a website that has served as an influential communications tool, informing the public and policy decision makers? By making older temperatures look lower and more modern temperatures look higher, global warming looks worse. But if they are just statistical tricks, torturing the data, it really makes them look worse... after the 'tricks' are exposed.
So what do we do the next time one of the Real Climate scientists comes out with alarming news? As some of even their critics acknowledge, their torturing the data may obscure the fact that global warming is actually happening--that we focus on their mistakes, not the data that is collected. Who is really being hurt by episodes like this?
Comments
Skepticism clearly belongs on the side of seeing way more political reasons to downplay global warming than to overstate the case.
This blog handles dollar signs strangely... Almost as though it were fed raw to ksh.
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