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Saturday, March 5, 2016

Michael Mann: No hiatus in attempts to misuse the science on global warming

There is no hiatus in attempts to misuse the science on global warming, says Michael Mann, a prime target of climate deniers

A sign warning people to in California to prepare for El Nino
El Niño influences global temperatures
Mark Boster/Los Angeles Times via Getty Images
by Michael E. Mann, NewScientist, March 4, 2016

Here we go again. Along with leading climate scientists, I recently argued there was a temporary slowdown in the rate of warming during the first decade of this century. For those who seem to miss the point, this means there was still an increase in temperature, but the rate of increase was slower.

The article (Nature Climate Change, DOI: 10.1038/nclimate2938gently took issue with a conclusion reached by Tom Karl, of the US National Oceanic and Atmospheric Administration, and his colleagues last summer (Science, DOI: 10.1126/science.aaa5632), that no such slowdown had occurred.

Climate change deniers are nothing if not predictable. Give them an inch and they take a mile. They seized on this to manufacture yet another fake controversy. Conservative news outlets claimed the two studies showed a fundamental schism within the scientific community and called into question the veracity of human-caused climate change.

Chief among the critics is right-wing provocateur James Delingpole. His article was headlined Now even Michael Mann admits the ‘pause’ in global warming is real; throws allies to wolves. The title itself is false.

What the deniers fail to disclose is that there is sufficient variation in the details drawn on by studies of the period – including which version of the temperature record is used and precisely what time intervals are being compared – that different researchers can come to different honestly held conclusions about what the data show. Respectable news outlets have accurately noted that.

And there is broad consensus among all the researchers involved on key points.

Inexorable march

First, there was no pause in global warming. Indeed, I have mocked such a notion as the “faux pause.” There was at most a temporary slowdown. With the record-setting temperatures of the past two years, that slowdown is almost certainly over now.

Second, any fleeting slowdown was almost certainly due to natural factors such as the El Niño/Southern Oscillation ocean phenomenon and the effect of natural drivers including volcanic eruptions and small but measurable changes in solar output.

These natural factors cannot slow the inexorable warming of the oceans and atmosphere resulting from anthropogenic pollution, they can at most mask it temporarily. The El Niño-ish conditions of the past two years may in fact herald the flip-side, with natural variability now adding to global warming.

Finally, despite claims by climate contrarians, the temporary slowdown does not indicate any discrepancy between climate model simulations and observations. Accounting for the vagaries of internal climate variability, the observations are seen to lie well within the spread of simulated temperature trends, as the figure below shows – the red line is observed temperature departures from the long-term (18802014) mean, the grey lines are model predictions.
Long-term temperature trends
Long-term temperature trend
There are enough legitimate issues to debate, when it comes to matters of climate change adaptation and strategies for reducing carbon emissions. At a critical moment for climate action, the last thing we need is fake debates. Shame there is no hiatus on that front.

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