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The Temperature Hiatus … Back Again

Dr David Whitehouse

If there is one topic that illustrates the state of climate science it is that of the so-called “pause” or hiatus – the observational fact that global surface annual average temperatures, as well as satellite data on the lower troposphere, hasn’t changed for a decade or more.

Many scientists have explanations for it, and there is the problem, too many explanations. There are over 30 suggestions at a conservative estimate ranging from the “it doesn’t exist,” to the oceans, volcanoes, stratosphere and almost everything in-between. Some scientists see the “pause” as a fascinating event that sheds light on the interplay between natural climatic variations and forced climatic changes, others strongly, sometimes too strongly, insist it doesn’t exist at all. In the battle for catch phrases that will stick it’s been called a “faux pause” as if so many other scientists were stupid and misguided to have ever entertained the idea in the first place.

Last month a paper in Science by Karl et al 2015 received a lot of publicity because, despite having the word “possible” in its title, many journalists and commentators, as well as some scientists who consider themselves to be a little of both, suggested that a revision in ocean temperature measurements removed the “pause” altogether. The paper was heralded as definitive, the last word, the “pause” was an artefact, busted.

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Wise heads took a broader view saying that it was not the last word on the subject. The latest paper on the “pause” might say one thing but the history of the subject, indeed of science itself, is that the latest paper is rarely definitive. Nonetheless unwise heads took it as the last word. One “journalist” tweeted that it was “amazing to witness the PR efforts going on at the mo by climate sceptic lobby groups…to dismiss the new Karl et al paper,” another tweeted, “you didn’t miss anything, the global warming “pause” never happened.

It never went away

Now from the same journal comes another paper Nieves et al, accepted for publication a month after Karl et al, that describes the “pause” and seeks an explanation for it in the way heat moves through the layers of the ocean.

They maintain that there has been cooling in the top 100 m of the Pacific, which has been compensated by warming in the 100 – 300 m layer of the Indian and west Pacific oceans.

I do hate graphs without error bars, and there are plenty of them in this paper. It’s all very well discussing errors elsewhere in the text of a paper but such details are easily skipped. Graphs are likely to be passed on and if they omit error bars they frequently achieve too great an authority if error bars are absent. Then the graph is passed on again and errors are then forgotten.

It is interesting to compare the trends in this recent paper and in Karl et al. Karl found 0.09°C for 2000-2014 whereas the new paper obtains 0.001°C for 2003 – 2012 so they are very different. Nieves et al found 0.008°C per year for 1993 – 2002. Indeed, they find substantially less warming in the top 100 m of the oceans in the current decade than in the previous one.

There is also no evidence for the much-raised suggestion by Kevin Trenberth that the ocean’s “missing heat” lies beneath 700 m. In fact, according to this paper, nothing much at all is happening below 700 m.

As far as the ocean surface temperature and the upper ocean heat content are concerned the “pause” or hiatus is definitely present.

Nieves et al say that the observational heat estimates do not reveal any obvious hiatus. They suggest that since the early 90s there has been a steady rate of ocean heat uptake. Other studies have proposed that the net ocean heat uptake was reduced during the 00s.

Overall Nieves et al opt for an explanation for the “pause” or hiatus being a result of the redistribution of heat within the ocean, rather than a change in the net warming rate. However, given the uncertainties I don’t think that this paper lives up to its self-proclaimed “most definitive explanation of how the heat was redistributed” during the hiatus.

It will be very interesting to see how the media react to this paper given that so many proclaimed Karl et al as the “answer” to the pause in the sense that it did not exist. Given that this paper is in the same journal with the weekly tip-sheet from Science having been in journalists inbox for four days before publication there is no excuse for not being aware of it. But as for writing it up and contradicting the certainty expressed after the Karl et al paper, we will have to see.