People don’t talk about how global warming has stopped, paused or slowed down all that much any more — three consecutive hottest years on record will tend to do that to a flaky meme. But there was a time a few years ago when you couldn’t open your news feed without being told global warming had stopped by some conservative columnist, climate science denier or one of those people who spend their waking hours writing comments on stories like this.
The issue at hand was one of the multiple measurements used by scientists to monitor the state of the planet — the globally averaged temperature.
Depending on which particular set of data you looked at, and how you calculated trends, there was an argument that temperature rises had slowed over a period of about 15 years. When deniers and contrarians talked about this “slowdown” the implication was that somehow, the laws of physics had suddenly changed and loading the atmosphere with carbon dioxide might not be a problem any more. As I argued three years ago, this global warming pause was never really a thing.
Despite all the other indicators of global warming showing business as usual — sea-level rise, temperature extremes, glacier melt, species movements, ocean heating, permafrost melt — the unhealthy fixation on one aspect, the average temperature of the globe, stuck firm. But scientists reacted to the public commentary in the only way they know how. They started to study this “pause” to find out what might be going on. They published scores and scores of papers in academic journals. This, in turn, fed a narrative that in the public eye that the fundamentals of human-caused climate change were in doubt when, in fact, none of the credible studies found this to be the case.
Some argued the pause did not exist at all, others looked at the role of the oceans, the trade winds, greenhouse gases, volcanic eruptions or even the way ship thermometers recorded the water temperatures (and then how scientists accounted for the different methods). But many scientists agreed too that the wobble in the temperature was well within the bounds of what’s called “decadal variability” — the natural ups and downs in the climate system that are superimposed on top of the warming caused by burning fossil fuels.
As the contrarian talking point went, the existence of different studies coming to different conclusions was proof that enough that policymakers should wait rather than act. In one paper that appeared in the journal Bulletin of the American Meteorological Society, three researchers argued that the scientific community had unwittingly been distracted by the claims of global warming contrarians.
Now a new study in the leading journal Nature has tried to reconcile the differences between the various pause studies and make suggestions about what went wrong. There was not a clear and agreed definition of what a pause was and if it was consequential. Scientists didn’t always communicate nuances clearly. “In a time coinciding with high-level political negotiations on preventing climate change,” write the authors from Switzerland’s Institute for Atmospheric and Climate Science, “sceptical media and politicians were using the apparent lack of warming to downplay the importance of climate change. It is easy to paint a controversial picture, but as often the devil is in the detail.”
Just to be clear, this was never about whether or not the threat from global warming caused by burning fossil fuels was in doubt for a while a few years ago. It wasn’t. Indeed, the Nature paper concludes that out of all the studies, the community is “more confident than ever” that human activity is now dominating the warming of the planet. But I’ve asked several leading climate scientists for their take. Dr James Risbey, a senior research scientist at CSIRO who has co-written an accompanying commentary in Nature, told me: “It never hurts to go back and see how we did.” But he said: “A short-term trend was too blunt an instrument to speak directly to our confidence in climate change anyway, but its overall relevance is that it helped us to explain the bumps along the way.”
The Penn State University climate scientist Professor Michael Mann (he of the hockey stick graph) expected the Nature paper would gain attention because of the high profile of the journal and that it was talking about the “faux pause”. But in an email he wrote there were no real “bombshell” findings in the Nature paper.
“The work of many groups, including our own, has shown that [climate] models and observations are consistent in terms of long-term warming, and that this warming — and recent extreme warmth — can only be explained by human activity, namely the burning of fossil fuels,” Mann said. Professor Stefan Rahmstorf, of the Potsdam Institute for Climate Impact Research, said: “I think the main lesson to be learnt from this discussion, by scientists, the media and the public alike, is to be highly sceptical of narratives pushed by so-called climate sceptics.” Rahmstorf was a co-author on a paper in the journal Environmental Research Letters in April which found neither the claimed “pause” nor the recent spikes in global temperature were outside the bounds of how the climate should be expected to react when it is loaded with extra greenhouse gases. He added: “Global temperature is a noisy data set due to natural short-term variability, and the debate was all about the noise and not about any meaningful change in the global warming signal.
Let me add that understanding the precise nature of this short-term variability is of course a very interesting science question, and work done on the so-called ‘hiatus’ has certainly improved our understanding of that a lot. “Incidentally, when in the journal Science in 2007 we pointed to the exceptionally large warming trend of the preceding 16 years, which was at the upper end of the [climate] model range, nobody cared, because there is no powerful lobby trying to exaggerate global warming. “And of course in our paper we named natural intrinsic variability as the most likely reason. But when a trend at the lower end of the model range occurs it suddenly became a big issue of public debate, because that was pushed by the fossil fuel climate sceptics’ lobby. There is an interesting double standard there.”
Professor Matt England, of the University of New South Wales Climate Change Research Centre, is another scientist to have carried out research in response to the “hiatus” and found that a change in the strength of trade winds was also a factor in holding temperatures down. “Yes, the post-2000 slowdown was totally real,” he said. “Just like the acceleration in surface warming between 1980 and 2000 was totally real. It’s called decadal variability, and it’s superimposed on the long-term warming trends. Studying the physical mechanisms giving rise to decadal variability is an important component of the work we do, and will continue regardless of definitions of surface warming slowdowns and accelerations.”
So what to make of it all? The short version is that global warming didn’t stop, scientists knew global temperatures would wobble around and climate scientists aren’t always the best communicators. But also, to paraphrase Stefan Rahmstorf, climate sceptics are not really sceptics at all.
— Guardian News & Media Ltd
Graham Readfearn is a freelance climate and environment journalist and writes the Guardian’s Planet Oz blog.
