A couple of weeks ago a great fuss was made about an article by Tom Karl and others, ‘Possible artifacts of data biases in the recent global surface warming hiatus.’ You can see the abstract and the whole paper here. At first only the abstract was available, with open access expected. I thought I’d wait until the paper was available before commenting, even though many others had already done so. Perhaps they had access through universities and other institutions, a benefit I don’t possess. It has been some time since such a lot of energy has been expended on a single article, and part of the reason is that the authors say that the supposed ‘hiatus’ in global warming, which even the IPCC accepts, is false: global warming has been there all the time. I’d better use the precise words of the article, which are that the results shown in the paper do not support the notion of a global warming “hiatus.” That take-home message was broadcast everywhere, even in the Antipodes.
Tom Karl is the Director of the US National Climate Data Center of the National Oceanic and Atmospheric Administration, and is a genuine big wheel. His Center’s work and indeed his own have been much used by the IPCC, and he has his own dataset as well. When you read the article closely, it is in fact largely about reconstructing ocean temperatures, on the ground that they need reconstructing. When the reconstruction has been done — Lo! His amended new dataset shows that the warming of the first fifteen years of the 21st century is at the same rate as that of the second half of the 20th century.
Well, on this occasion the proof is both in the pudding and in the eating. Why do we need reconstructed SSTs (sea surface temperatures)? The Karl explanation is that there is a difference between the results of temperature buoys and the temperatures calculated from ships. The buoys show a cooler temperature than the ships. I have also discussed the errors in SST measurement before, and in my view SSTs before the Argo buoys that came in 2003 are just about worthless in any time series. There are just so many different kinds of error that it is impossible to ‘correct’ for them all.
Nonetheless Mr Karl felt it had to be done, and what he did was to increase all the temperature data from the buoys to accord with the data from the ships. That of course makes the whole SST trend much warmer, and the 21st century is now apparently a much warmer period. Oh, and the so-called ‘hiatus’ seems to have disappeared. Because a ‘hiatus’ is a gap in a series (from Latin, hiare, to gape), there is now, at least according to Mr Karl, no gap, and warming has continued unabated. I’m not sending it all up. This is the argument I gained from reading the paper.
Now, if you were a serious scientist , what would your next move be? You have the new data series. Wouldn’t you now compare your results to all the other results that are built on SST measurements? There’ll be differences, of course, and you’ll need to have a plausible account of why yours are better (or theirs are worse). The five standard global climate datasets are well-known, and the accompanying graph shows what they say about global temperature anomalies in the last twenty years.
The datasets vary in terms of how high the anomaly trend is, but they show the same movements, by and large. So the Goddard Institute of Space Science’s gistemp shows the highest anomaly, and RSS (Remote Sensing Systems, a satellite system) probably the lowest. But they all show the same movements, up and down.The horizontal lines show how long there has been a zero trend (no warming or cooling), and the colours of the lines tell you which dataset is which. That applies also to the vertical lines. It’s a bit cramped, for which I apologise. There are many versions of this diagram, and they are all based on publicly available data, from those who prepare the statistics.
And what they all show is a lack of warming. I don’t like the ‘hiatus’ term because it implies a resumption of warming, which may or not occur for who knows how many years. Even gistemp shows the zero trend though only for ten years. Now it is true that all journal article are but contributions to the larger quest for knowledge, and that each paper’s results are not definitive — or if they are, then we will not know that until many years later, and if the paper is really important, and in the right field, then a Nobel Prize may well be on its way.
It seems to me that if you are going to tell the world that your work does not support the notion of a global warming hiatus you had better show not just that you have some fancy new reconstructed data, but that your data are just miles better than everyone else’s, if only because nobody else agrees with you, and they’ve been in the business for a long time. Not only that, despite the fact that the datasets are based on different techniques, there is a strong measure of agreement among them.
Alas, the Karl paper doesn’t even mention anyone else in the temperature-measuring field. I pressed on into Supplementary Materials attachment and found this gem: Previous versions of our SST analysis included satellite data, but it was dis-included in a later release because the satellite SSTs were not found to add appreciable value to a monthly analysis on a 2° grid, and they actually introduced a small but abrupt cool bias at the global scale starting in 1985 . Other observing systems, including satellites, and model simulations could provide important insights that would enable the quantification of interpolation uncertainties in data-sparse regions, but haven’t been used in this study.
Why not, you ask, and then shrug. OK, Mr Karl only offered his work as a ‘possible’ explanation, but he did so with such hullabaloo that one can only conclude that the reason for the paper, whose account of reconciling ship SST measurements is awfully unconvincing (see Ross McKittrick’s offering here), is political, not scientific. By that I mean that the Karl paper is just another in the almost weekly production of ‘scientific’ work that seems intended to justify the whole world getting together in Paris at the end of the year, and at last producing a global agreement on curbing greenhouse gas emissions.
I notice that Graham Lloyd of The Australian is inspecting these productions with real critical skill. It would be lovely if the ABC and the Fairfax Press could do likewise. But, at least at the moment, that is to hope for too much.
Footnote: There are more than a dozen examinations of the Karl paper on the major climate websites, and they are all critical save for the one on RealClimate, which is nonetheless somewhat opaque. A summary can be found on Climate etc, here.
I have written about the sea-surface temperature-measurement problem here: