How To Get Rid Of The Warming Pause – Again

  • Date: 27/11/15
  • Dr David Whitehouse

The hiatus in annual average surface temperature does not exist and never has and is a myth created by climate sceptics. That’s what a new paper claims. What’s more its very description as a “hiatus” or a “pause” is dangerous because it misleads both scientists and the public.


The paper in question is published in the journal Scientific Reports and its authors are Stephan Lewandowsky, James Risbey and Naomi Oreskes. Consider the first sentence of the abstract: “Recent public debate and the scientific literature have frequently cited a “pause” or “hiatus” in global warming. Yet, multiple sources of evidence shows that climate change continues unabated, raising questions about the status of the “hiatus.”

It is a scientifically convoluted sentence. The hiatus refers to the global annual average surface temperature which is just what it says it is. It is also confirmed by lower atmospheric temperature measurements made via satellites. Together they provide an interesting perspective on the problems of data collection, particularly the gaps and the infilling of ground measurements. It is fair to say that nobody expected a period of about 15-years with no increase in these measurements and it is therefore a valid talking point raising questions about model-data comparisons. Some say global warming has stopped but that is different from the existence of the hiatus. One should be careful in assuming that a hiatus in these datasets is akin to a similar hiatus in “global warming” so language must be used more carefully than this. My impression is that sloppyness in the language used in this paper actually determines some of its conclusions.

The paper continues: “In the public sphere, the claim that global warming has “stopped” has long been a contrarian talking point. After being confined to the media and internet blogs for some time, this contrarian framing eventually found entry into the scientific literature.” The paper continues: “The notion of a “pause” or “hiatus” demonstrably originated outside the scientific community, and it likely found entry into the scientific discourse because of the constant challenge by contrarian voices that are known to affect scientific communication and conduct.”

This misrepresents what actually happened. The first mention of a pause was in 2006 and by 2008 it was being discussed in the peer-reviewed scientific literature. However, those who have read the Climategate emails will be aware that, according to one scientist, the scientific community knew all about it and had, in private, either dismissed it or were somewhat worried. The hiatus was incorporated into peer-reviewed literature independently of what was going on in blogs. It originated from Robert Carter, former professor of earth science at James Cook University in Australia. Was he outside the scientific community at the time?

The paper is also wrong in its claim that the hiatus is “ineluctably tied to the contrarian claim that global warming has stopped.” What the authors fail to appreciate is that the motivation of most sceptics, like scientists, is to find out what is going on and what is happening to surface and lower atmospheric temperatures. One may argue that this has been good for science as nowadays we have a very different view of decadal climatic variations than we did a decade ago. Remember that were we told that mankind’s temperature signature was dominant. Today we are told that the decadal variations are dominant and we have to wait a while for the anthropogenic signal to emerge. This is a fundamental turn around for climate science.

To prove its stated conclusion the study analysed 40 peer-reviewed papers that mention the pause or hiatus. The paper says that, “Articles were sourced by the authors with the help of a number of other researchers and climate experts who are conversant with the current literature.” They are a peculiarly selected corpus, for example, thirteen of them did not use either HadCrut4, NasaGiss or NSDC datasets. The paper extracts hiatus duration as well as start and end points from them.

The lines on the map moved from side to side

The paper states that “there is no agreed “hiatus” period in the scientific literature.” As if that really matters or is indeed feasible given the statistics of the data. A year or two is the best accuracy one is going to get and often papers will be loose and disagree with their start and end points. Failure to agree on an exact year does not invalidate the existence of the hiatus. When did the hiatus begin? Two papers said 1997, ten said 1998, one said 1999, eleven papers said 2000, and seven said 2001. More than half of the papers maintained that the hiatus began between 1998 and 2000.

Now it is all very interesting to examine why the authors chose those dates but it tells us very little about the science of the hiatus without familiarity with the data. It has long been recognised that starting in 1998 is unwise as 1998 was a very strong El Nino year. 1999 and 2000 were La Nina years which makes it unwise to start there also. At a stroke about half the papers in the study are suspect in terms of calculating the duration and trends of the hiatus. As for the others the study gives to much weight to their vague estimates of when the hiatus start and end points.

The authors compared the distribution of warming trends during the hiatus as it is defined by the papers they study with the distribution of all possible trends that have been observed during what they describe as “modern” global warming. They show those trends with three different start dates. Note that there are no errors on the trends, which will be considerable, and also note that the trends are weighted according to their popularity in the selected literature. Adding appropriate errors to the trends would have smeared out these graphs.

Their graph shows a graphical representation of the warming trends that were observable given the available data at the time for any vantage point between 1984 and 2014. They say that for each vantage point the previous seventeen years always showed a warming trend. Anyone looking at the data would see that this is a trivial point. They claim that at 2014 you can go back 14 years with no significant trend so one could conclude that this study has found a hiatus (looking at the papers it studied it was obvious it would) although it does not consider it significant. The study says “the hiatus is an unexceptional fluctuation.” It adds: “The hiatus has always been there even when the sample size is small.” This second point is wrong. What can be reliably concluded from small sample sizes is determined by their errors, which are large.

What worries me considerably about the paper is its marshaling of evidence. For example, it states that timescales of at least 17 years are known to be necessary for noise reduction and detection of a signal. Such a bold statement demonstrates something is wrong in the dna of this paper. It is a reference to a well known paper by Santer et al (2011) which, like all scientific papers, is an claim and not a fact, yet it is treated as if it were a certainty. A conclusion based on a claim is not the same as a conclusion based on a certainty.

Haven’t you heard it’s a battle of words

Indeed I felt that at the heart of this paper is an attitude of “us and them.” The hiatus is deliberately associated with contrarians and it is claimed it came from outside the scientific community and has spread almost like an infection. In my view the detection and assessment of the hiatus has been one of the triumphs of modern science and its emergence reflects the way the nature of science itself is changing. The “us and them” is changing. The world is full of very clever people, often as educated and experienced as “professional” scientists and frequently talented in areas that many climate scientists are not. For the first time they have access to the journals and sometimes even the raw data and statistical tools and finally the ability to disseminate their findings. Science has grown wider and is under more scrutiny than ever before, and that is an historic, wonderful thing. The discovery of the hiatus is part of this new development.

Despite this flawed paper the hiatus is one of today’s major research areas in climate change. In the last few months alone it has resulted in papers published in the American Journal of Climate Change, Geophysical Research Letters, Nature, Nature Climate Change and Climate Dynamics.

Naomi Oreskes is quoted in the Guardian about this paper. However she makes a fundamental mistake. “For a long time, climate change contrarians and deniers have insisted that global warming has paused, stopped, or taken a hiatus. This might have been dismissed as the usual denier cherry-picking—since much of it was based on cherry picking the starting year of 1998—an unusually hot year.” The 1998 effect is irrelevant to the hiatus, always has been, but it keeps on being repeated.

And therein is the danger perhaps unwittingly exemplified by this hiatus-myth paper. It is the headline “the hiatus never existed” that will be repeated and some will accept it as a fact, and sooner or later someone will say that this paper proves the hiatus never was. The framing of the debate about climate change often comes from unquestioning obedience of top lines, titles and memes, for example that the hiatus is unquestionably disproven, or that 97% figure.

The main conclusion I draw is that if you want to examine the hiatus or pause then look at the data itself not the vagueness of a cherry picked selection of researchers with a big axe to grind. And as for the hiatus or pause being disproven, here is a graph of it minus the recent strong El Nino. There is no mention of 1998.

Screen Shot 2015-11-27 at 11.52.09Click on image to enlarge.

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