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Top scientists insist global warming really did slow down in the 2000s

Ice calves from the Northern wall of the Perito Moreno glacier in Los Glaciares National Park, part of the Southern Patagonian Ice Field, on Nov. 29, 2015 in Santa Cruz Province, Argentina. (Photo by Mario Tama/Getty Images)
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You could be forgiven for not being able to keep up with whether scientists do, or don’t, think global warming “paused” during the early 2000s.

First, the U.N.’s Intergovernmental Panel on Climate Change told us, in a definitive 2013 report, that there had been a real slowdown of global warming over the past 15 years. It noted that the rate of warming during the period from 1998 through 2012 was  “smaller than the rate calculated since 1951,” although the body also cautioned that “Due to natural variability, trends based on short records are very sensitive to the beginning and end dates and do not in general reflect long-term climate trends.”

Nonetheless, this idea of a global warming slowdown or “pause” was endlessly cited by climate change skeptics and deniers circa 2013. However, more recently, scientific reports have begun to come out challenging the notion.

A dataset update from the National Oceanic and Atmospheric Administration, aimed at removing biases in the data, wiped out the “pause” — to much fanfare and controversy. “Newly corrected and updated global surface temperature data …. do not support the notion of a global warming ‘hiatus,’” the study found. Other recent research, meanwhile, has suggested that the notion of a pause may represent a bias among scientists themselves, has been defined in curiously inconsistent ways by researchers – and in any event, always seems to go away if you simply analyze a long enough time period.

Seas are now rising faster than they have in 2,800 years, scientists say

That’s what makes it so striking to find that this debate is very much not over — a group of top scientists has just published a paper in Nature Climate Change robustly defending the idea that, as they put it, “The observed rate of global surface warming since the turn of this century has been considerably less than the average simulated rate” produced by climate change models.

The authors include noted climate researchers Gerald Meehl of the National Center for Atmospheric Research, Benjamin Santer of Lawrence Livermore National Laboratory, and Michael Mann of Penn State University. The research was led by John Fyfe of the Canadian Centre for Climate Modelling and Analysis at the University of Victoria.

The authors also argue that a large body of research into the causes of the apparent slowdown — which tended to target natural fluctuations, and especially the behavior of the Pacific Ocean — represents valuable work that advances our understanding of “a basic science question that has been studied for at least twenty years: what are the signatures of (and the interactions between) internal decadal variability and the responses to external forcings, such as increasing GHGs or aerosols from volcanic eruptions?”

To be sure, the researchers behind the current paper absolutely do not think that global warming is over or anything of the sort — rather, the argument is that there was a real slowdown that’s scientifically interesting, even if it was brief and is now probably over. After all, even if they paused, temperatures now seem to be rising again, with 2014 and 2015 setting back-to-back global temperature records.

Or as Ed Hawkins, one of the researchers and a scientist at the National Centre for Atmospheric Science at the University of Reading, put it on his blog when the paper emerged: “climate scientists agree that global warming has not ‘stopped’ – global surface temperatures and ocean heat content have continued to increase, sea levels are still rising, and the planet is retaining ~0.5 days of the sun’s incoming energy per year.”

Stephan Lewandowsky, a psychologist at the University of Bristol in the UK who has co-authored a series of papers questioning the pause, sent a comment in response to new paper by John Fyfe and his colleagues. Lewandowsky said one reason matters are confusing is that there are multiple issues swirling here, and the main one he has taken issue with is the idea that global warming has stopped. A brief slowdown, if it existed, doesn’t show that.

In contrast, Lewandowsky argues, the new paper underscores something different — it is investigating whether temperatures in the 2000s did or did not match what climate change models had expected. And the new study says they did not.

“As far as we are concerned,” Lewandowsky said by email, “there is no discrepancy between us and Fyfe et al. as we address two distinct scholarly questions–and they agree with us about the ‘warming didn’t stop part,’ which is the only thing we addressed.”

The new study set off a flurry of tweets by leading climate scientist Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies, who argued that there is really no long term let up in warming, but that nonetheless, it could be scientifically interesting to try to understand the reasons for a short term one. Here are some examples:

Still,  there’s a giant elephant in the room. Researchers can draw nuances and distinctions about what they mean and don’t mean, but the problem here has really always been the un-nuanced way that “pause” research has been cited in the broader debate, in order to undermine the idea of human caused climate change — even though none of these researchers think that it actually does that.

Indeed, the new publication is sure to re-awaken the highly politicized debate over the “pause” — so high profile that it was at the center of a recent congressional investigation, by Rep. Lamar Smith (R-Tex.) of the House Committee on Science, into the NOAA researchers who challenged the pause’s validity in 2015.

A leading presidential candidate, Ted Cruz, also continues to make a pause-like argument to undermine the idea of climate change, although he takes a somewhat different tack, citing satellite data that also, he says, appear to suggest a “pause.”

Thus, in the end, scientists may well reconcile over the “pause” — acknowledging that it was real, brief, and interesting, but no reason not to worry about the planet — but the fact remains that for the rest of society, this debate was anything but purely scientific.

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