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expert reaction to climate hiatus statistics

Publishing in Environmental Research Letters scientists examined global-mean surface temperature trends, taking in to consideration a recent series of three record-breaking years in a row.


Prof. Chris Rapley, Professor of Climate Science, UCL, said:

“This robust new analysis of global surface temperature data consolidates the results of recent studies that show that global warming has continued unabated since the 1970s. The Earth’s energy budget is out of balance, and will remain so until human carbon emissions are reduced to zero and equilibrium is restored. In the meantime heat continues to accumulate. The analysis underscores the need to adopt a time resolution of 15 y or greater to obtain reliable results in separating the temperature trend from intrinsic variability. Using shorter time resolutions and cherry-picked time periods is a recipe for misleading conclusions.”


Prof. Richard Allan, Department of Meteorology, University of Reading, said:

“This well-conducted study shows that slowing in global surface warming at the start of the 21st century is not very obvious when avoiding naive statistical methods. Yet unusual climate conditions did affect this period and generate rates of global surface temperature increases slower than the expectation based upon hundreds of detailed global simulations. So the idea of a ‘slowdown’ or ‘hiatus’ is not make believe.

“Fluctuations in the climate system combine with the warming trend due to human-caused emissions of greenhouse gases. It is unsurprising that these unpredictable fluctuations take place but scrutinising them helps scientists more fully understand the complexities of the climate system.”


Prof. Andrew Watson FRS, Royal Society Research Professor at the University of Exeter, said:

“This paper uses very straightforward statistics, and supports several recent studies coming to similar conclusions. They find there is no basis for thinking there was a change in underlying global temperature trend during the period that has been called a hiatus or pause.

“Global temperatures have followed a steadily upward trend since about 1970, with however, important short-term natural variations superimposed on the trend. Temperatures did increase relatively slowly during the decade of the 2000s, but this paper shows it was an unexceptional slowdown given this short term “noise”. Equally, the recent series of several record warm years in a row is unexceptional in a statistical sense, it’s all consistent with the short term noise.

“Understanding the reasons for the short-term variations is interesting and important, and is the subject of ongoing research. However, for the long term trends, the study adds to our confidence in the basic science: this says that the Earth is warming as greenhouse gases are added to the atmosphere. We have known about that for a very long time.”


* ‘Global temperature evolution: recent trends and some pitfalls’ by Rahmstorf et al. will be published in Environmental Research Letters on Tuesday 25th April. 


Declared interests

Prof. Rapley: “No interests to declare.”

Prof. Allan: “No conflicts of interest.”

Prof. Watson: “I am a research scientist, employed by the University of Exeter. I hold various research grants from the Royal Society, the Natural Environment Research Council and the European Commission, to study sources and sinks of greenhouse gases such as carbon dioxide and methane. I don’t have a connection with the current study and have not co-authored papers with its authors.”

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