I am already on record saying that I think McLean, DeFreitas and Carter (JGR 2009) should never have passed peer review. Indeed, I think I was the first of the science-conscious bloggers to call attention to this extremely weak paper as well as the ridiculous inflation of its importance in anti-climatology circles.
The whole thing is easily refuted: it attempts to correlate temperature trends to the phase of the El Nino oscillation (the “ENSO index” in an especially awkward but stubborn piece of meteorological jargon). But the first step in the analysis is to take a running difference between temperature measures. Of course, the first difference is a linear operator which reduces any linear trend to exactly zero. Among its other effects, it REMOVES THE TREND. Thus, whatever any subsequent analysis does, it cannot shed any light on the trend. This is obvious, and the paper only refers to the trend in an ambiguous throwaway in the conclusions. This did not prevent the anti-climatology people from trumpeting it as yet another “final nail in the coffin” for “the global warming theory” etc. etc. It was an especially illustrative example of the sort of excess the naysayer blogs propagate with impressive regularity. But given the overreach, and the prominence and effectiveness of the rebuttal, you’d expect this one to just slink away quietly.
Michael Mann is being mendacious when he describes the 2009 paper of which I was lead author as “bad science”. The criticism of our paper was seriously flawed. It focussed on the Analysis, rather than either the Discussion and Conclusions; it falsely accused us of saying that the IPCC 4AR did not say something when our paper actually cited the 4AR and described what it said; and it deceitfully tried to claim that a Figure was flawed. The criticism was an artful piece of misdirection whose abstract was contradicted by its own Introduction. When we tried to respond the peer review of our response was devoid of any integrity whatsoever, reflecting badly on the reviewers and the journal itself. To deny us the right of reply on such an important matter was unconscionable. We told our point of view in “Censorship at the AGU: Scientists denied right of reply” (see http://scienceandpublicpolicy.org/images/stories/papers/originals/agu_censorship.pdf). Unlike Michael Mann’s “Hockey Stick”, we described exactly what we did and how we did it, rather than withhold information for years. Mann’s claim that our paper was “bad science” is a claim without any substance whatsoever.
For reference, I have transcribed the relevant passages from Mike’s book. (Hurriedly as I am on the road and my Kindle is complaining of a low battery. Apologies for any mistranscription.)
Another head of the hydra was a 2009 paper by John McLean, Chris de Freitas and Bob Carter published in JGR in the innoccuously titled “Influence of the Southern Oscillation on Tropospheric Temperature”, the authors claimed that el nino drove essentially all variations to global temperature – a distinctly odd claim since almost nothing in climate science has been mroe closely studied than the relationship between el nino and global climate. It was well known – and in fact had been demonstrated most recently in an article in Nature – that, while el nino, along with volcanic eruptions, did explain a fair amoount of the short-term year-to-year variability in global temperatures, it could not accouny for the warming trend., Had McLean et al somehow discovered something that had eluded the entire research community fir decades? The claim was indeed extraordinary, And the evidence? Not so much.
The study’s principal findings were, yet again, the product of a surprisingly basic error. The authors hadn’t, as it turned out, actually analyzed the statistical relationship between El Nino and global temperatures. They had instead analyzed the relationship between El Nino and the rate of change in global temperatures. That, combined with some additional unwarranted processing of the data, ensured that in the end all McLean et al. had done was to confirm the well-known fact that El Nino explains a fair share of the year-to-year fluctuations in global mean temperature. Their analysis provided no basis for any conclusions regarding climate change, Most of these facts were pointed out by various climate bloggers within a few days of the publication of the paper. It took nearly a year, however, for a peer reviewed refutation to appear in the literature.
In the meantime, the authors once again generated substantial publicity for their claims. Climate science “swiftboater” Marc Morano (see chapter 3) used his Climate Depot blog to hype the study. In a press release boldly titled “Nature, Not Man, is Responsible for Recent Global Warming,” study coauthor Bob Carter claimed that the findings left “little room for any warming driven by human carbon dioxide emissions”.
I will take the opportunity to repeat one of the comments from the RealClimate discussion, which is a clear and succinct summary of how most of us view the story. Ron Taylor wrote:
I have been reading and rereading this post and the comments, but still find the whole thing strangely puzzling. It seems to me that any good first year calculus student should be able to quickly find the fatal flaw in the methodology as a way of explaining temperature change (as opposed to temperature variability, since it discards any secular component). So I thought they were being really clever by making a valid correlation of SOI with temperature variability, then subtly changing the language to temperature variation. Many people, including journalists, would conflate temperature variation and temperature change, with no further effort required on the part of the authors. It looked like an example of: “If you can’t convince them with facts, then dazzle them with footwork.”
But then they claim in the press release that it actually explains temperature change, and they do so with no apparent embarrassment. Unless I am really missing something it seems incomprehensible that anyone in the scientific community would take this paper seriously.
Of course, the pythons have a different sort of summary: