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Global warming trend with ups and downs, but without slowdown or speed-up

04/25/2017 - Temperatures worldwide are increasing due to greenhouse-gases from fossil fuels. Past claims of a noteworthy ‘slowdown’ of the global warming trend are proven wrong by statistical analysis, a new study shows. Researchers from Germany and the US examined global-mean surface temperature trends, in the light of the three record breaking years 2014-2015-2016 in most datasets. While there of course is some natural short-term variability, the study finds no significant slowdown let alone ‘pause’ in the upward trend.
Global warming trend with ups and downs, but without slowdown or speed-up

Trends in global temperature according to changepoint analysis (Fig.2 of Rahmstorf et al, 2017)

“Short-term fluctuations are normal in global temperature, and they can be deceptive,” says lead author Stefan Rahmstorf. “Because fluctuation is ever-present, it is important to tell the difference between genuine trend change and appearances that are merely the manifestation of ‘noise’”. Most scientific publications that discussed an alleged ‘hiatus’ have not provided a thorough statistical assessment. The scientists, including two statisticians, examined five separate global temperature data sets – the NASA GISTEMP, NOAA, HadCRUT4, the revision of HadCRUT by Cowtan and Way, and the Berkeley Earth Surface Temperature BEST.

Although the global temperature data show short periods of greater and smaller warming trends, and even short periods of cooling, the team’s key question was whether or not these are statistically significant in showing a change in the form of a slowdown or acceleration of global warming, or whether they are merely expected fluctuations – or noise – in the data. “We found that it’s all in the noise,” says Rahmstorf.

“The public discussion of time intervals within the range 1998 to 2014 as somehow unusual or unexpected – indicated by terms like 'hiatus' or 'pause' – has no support in rigorous study of the temperature data,” says Rahmstorf. “Nor does recent talk of a sudden acceleration based on three record-hot years in a row and the exceptional value in 2016. Global warming is not slowing down or speeding up, it just continues relentlessly over the past decades.”

Article: Stefan Rahmstorf, Grant Foster, Niamh Cahill (2017): Global temperature evolution: recent trends and some pitfalls. Environmental Research Letters [DOI:10.1088/1748-9326/aa6825]

Weblink to the article: http://iopscience.iop.org/article/10.1088/1748-9326/aa6825

Weblink to video abstract: http://bcove.me/03ruj25t

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