Friday, May 30, 2008

A blip in the temperature record

An article in Nature concludes that a previously unexplained dip in global sea surface temperatures (SSTs) in the 1945 is actually due to a change in the way measurements were taken at the end of WWII. You can see the dip in the IPCC's temperature plots - look at the global ocean's observed line.

Until we developed global satellite coverage in the 1980s, SST was measured by ships and the methods - buckets brought on deck, buckets dropped in the ocean, etc. - changed over time. The people who put together the global SST datasets expend a ton of effort analysing and accounting for the measurement bias caused by the different methods. As RealClimate explains, this discovery did not come out of the blue, to use some ocean lingo. It is builds upon the ongoing analysis of bias in different measurement methods.

The article and the accompanying News and Views summary in Nature explains the likely implications for the global temperature record. The 0.3 C blip due to the 1945 switch in methodology likely means the immediate post-war SSTs were underestimated. In that case, it would reduce or eliminate the "observed" cooling in the late 40s and the 50s, a period that has flummoxed climate modelers, not alter the entire post-war temperature record. As the News and Views opens: "An unseen measurement bias has been identified in global records of sea surface temperature. The discrepancy will need correction, but will not affect conclusions about an overall warming trend."

Nonetheless, some have jumped on the paper as possible evidence of a problem with the basic conclusions of the IPCC. It is not. Once again, what we have is a case of impatience, of not looking (or reading the whole paper), before leaping.

7 comments:

Bishop Hill said...

Do you not mention Steve McIntyre either?

Simon Donner said...

Not on purpose. Bishop is referring the host of the blog Climate Audit. It turns out McIntyre made a similar discovery about the causes of the 1945 SST dip a couple years ago, and explained it in a blog post. Now many people appear angry that McIntyre was not given credit by Nature. That frustration - while perfectly understandable - is a bit misplaced. Since his work was not actually published, it will never get cited in a scholarly article.

It is a reasonable line to draw. You can't cite a blog post, ostensibly because a blog post is not subject to a structured review process. That's one key burden of proof in science. Now, complicating matters in this case, is McIntyre's reputation as a climate 'skeptic' who has for years highlighted potential flaws in the observed temperature record. Who knows, maybe Nature would not have considered his paper because of reputation? Then I'd say the outrage would be justified. Otherwise, well, if, as the saying goes, we scientists got a dime for every time we read a journal article that summarized something we already suspected to be true, or had indeed proven ourselves, well, this would be a far more lucrative profession.

Bishop Hill said...

Good.

However, I disagree with the theory that blogs can't be cited in scholarly articles. Nature itself recognises this - see its style guide.

I think it's fairly clear that Nature sees itself as part of the green movement. Their climate website links to lots of environmental campaigners but not to McIntyre, despite my regularly pointing out their oversight to them. One can observe the Maxine Clark, the executive editor of Nature, arguing the green line around various websites.

Simon Donner said...

I'm not going to defend or condemn Nature. True, many of us have wondered about some of the recent Nature commentaries (the Pielke et al. piece on the IPCC, for one). The fact is the science articles do still go through the standard peer review. The style guide, like any journal's style guide, explains how to cite a website because a lot of data is only found on the web (e.g. we often cite FAOSTAT, USDA's websites, Reefbase.org in our published work) not because it is acceptable to cite a blog. Who knows, that may change. Blog posts, including my own, are often not reviewed by anyone, let alone selected experts on the subject.

Bishop Hill said...

The authors of the paper have a choice - they can cite a blog or they can run the risk of people thinking that they are taking credit for someone else's work. This would bring both them and the journal into disrepute.

And besides not everything cited has to be reviewed. Citation of private communications is common, and I've been able to find examples of blogs being cited as far back as 2006.

Simon Donner said...

Of course, you could invert that statement. If the author of a blog post doesn't want to run the risk of other people getting credit for work he or she has already done, then he or she should write an actual paper.

Anyway, you can't use a blog as a reference for a scientific result in Nature (or Science or any top journal). Personal communications are generally limited to the source of as yet unpublished data or analysis, and are not acceptable to editors or reviewers in most circumstances.

Bishop Hill said...

You are surely correct that the best scenario would have been for McIntyre to write up his findings as a paper, although I don't suppose it's easy for unaffiliated authors to get published, particularly when their views run contrary to the mainstream.

Whether he did or didn't, I don't think this absolves the Nature authors of a duty to mention his work.

Interestingly, Craig Loehle mentions in a comment on Climate Audit that he has recently had a paper accepted by Climatic Change. He says he gives credit in the paper to McIntyre and Climate Audit.