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David Whitehouse: A Poor Analysis Of The Pause

Dr David Whitehouse, GWPF Science Editor

A new paper in Nature Climate Change concludes that the so-called pause in global surface temperatures never happened. The paper has been mentioned in a few media outlets. It claims that new data from the Arctic makes the pause go away – and so it seems until you look at the paper in a little more detail than news headlines suggest.

Xiangdong Zhang of the International Arctic Research Centre and colleagues produce a new estimate of the trend in global temperature that includes their new data on the Arctic. It is 0.112°C per decade, as opposed to a previous 0.05°C per decade, for the period 1998-2012. Once again one notes the unscholarly accuracy of a thousandth of a degree which is unwarranted by the errors in the data. They therefore conclude that the pause never existed.

For the Arctic they give a warming estimate of 0.659°C per decade making it, as expected, the fastest warming region on Earth. Consider for a moment what this means if one accepts the most recent analysis. Without the Arctic data the global temperature paused, i.e. only one region is contributing to global warming, and a region where it has been estimated about half is due to natural factors.

The trend calculations of surface temperatures carried out in the recent paper are inadequate. Over and over again it has been pointed out that start and end points must be variable, and errors properly accounted for, to obtain a fair estimate given annual variability. Their Figure 2 illustrates this point (click on the image to enlarge.)

Fig 2a is Arctic data, and Fig 2b global data. Note the absence of error bars and the use of a fixed start and end point – 1998 and 2012 – for the trend analysis. If one varies the start and end points by a small amount different results are obtained. It is surprising that a fuller treatment was not required for this paper given the long time it was in review by Nature Climate Change. It was submitted in January 2017 and accepted in October.

The global temperature pause is a fascinating topic in current climate science. Every week new papers explaining its existence and possible causation are being published in leading scientific journals. It is a pity that the papers accepting it and considering its implications do not receive the media attention given to those papers that say it has either gone away or never existed. It is also a sad comment on the current state of science journalism that media outlets publish uncritical summaries of the new paper in a tone of bashing “sceptics” who who were the first to identify the pause and have researched it ever since. Hundreds of climate scientists have been studying the pause and the latest attempt to deny its very existence is unlikely to change this research interest.

In the meantime, global temperatures have fallen to levels close to what they were before the 2015/16 El Nino and may drop further in the next few months. In short, reports of the death of the global warming pause have been greatly exaggerated.