The Washington PostDemocracy Dies in Darkness

You should not be surprised that climate predictions may have been too conservative

Two women look out of a hotel entrance over a flood barrier keeping back water from the Danube River in Passau, Germany, on Sunday. (Peter Kneffel/AP)
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The global consensus on how climate change will affect the planet is documented every few years by the Intergovernmental Panel on Climate Change (IPCC), an entity within the United Nations that compiles research on the subject with the assistance of thousands of volunteer scientists. The five reports compiled since 1990 have documented both updated estimates of the dire effects of global warming and the escalation of the factors that contribute to that warming.

And, year after year, those reports are criticized for being too conservative.

Over the weekend, the BBC reported on a new push for an international investment in computers capable of modeling the complex evolution of the global climate. Climate scientists, the BBC charged, had “failed to predict flood and heat intensity” — a failure exposed in the recent heat wave in the United States and Canada and in the recent flooding in Europe. The article included the above indictment of the IPCC’s estimates.

“The IPCC’s reports tend to be both conservative and consensus,” Bill McGuire, emeritus professor at University College London, told the network. “They’re conservative, because insufficient attention has been given to the importance of tipping points, feedback loops and outlier predictions; consensus, because more extreme scenarios have tended to be marginalized.”

Speaking to Axios, Lawrence Berkeley National Laboratory’s Michael Wehner similarly argued that climate scientists had erred in favor of less extreme predictions, in part out of concern that they might seem alarmist. But for anyone who has been tracking the IPCC’s reports over time, that the effects of climate change might extend beyond the projected estimates was always clear.

In 2003, John Houghton, then the IPCC co-chair, conceded that some people believed the temperature projections included in the group’s first report — released in 1991 and which informed the international Kyoto climate accord — showed that “the IPCC was far too conservative and should have been bolder” even then. In 2005, he adopted that position himself, telling a Senate committee that “IPCC reports have consistently proved to be too conservative” in their estimates.

Over and over this crops up. James Hansen, the scientist whose 1988 testimony before Congress kick-started the focus on climate change, described the IPCC as being overly cautious in a 2004 interview, specifically referring to its consideration of the potential ramifications of the collapse of the Arctic ice sheet. Michael MacCracken, head of the Climate Institute in Washington, previewed the IPCC’s 2007 report by noting that it had consistently erred on the side of less-bad outcomes.

“Scientists don’t like to be wrong, so they tend to discount the most uncertain things,” MacCracken told USA Today. “And that’s good, but policymakers and risk managers usually want to know the worst case, as well as the middle one, when they plan for things.”

In the aftermath of that report, the IPCC’s fourth, there was a broad array of critics opining that its estimates may not have accurately conveyed the dangers posed by warming. Some of that feedback was certainly a function of an activist movement newly empowered by the prominence of climate change in the political debate (largely a function of the release of “An Inconvenient Truth” the year prior), but much of the criticism came from scientists themselves — including some familiar names.

“I doubt that there have been any explicit attempts to influence the content,” McGuire said that year. “But I do worry that the conservative tenor may at least partly reflect a wish not to antagonize the U.S. government. In the future, the IPCC needs to say what it really feels about climate change.”

But McGuire wasn’t alone.

“At times it is frustratingly conservative,” University of Chicago climatologist David Archer told Inter Press Service that year.

In 2013, in advance of the fifth report, the New York Times reported on the broad sense that the IPCC was overly cautious, identifying two contentious issues — each of which was decided in favor of the more conservative position. Research from MIT and another group of American scientists found that the IPCC’s models were overly optimistic or ignoring the possibility of negative feedback loops, a situation in which one negative effect worsens another negative effect. (Thawing permafrost from rising temperatures in the Arctic, for example, can release more methane that contributes to warming.)

As the era of social media matured, those criticisms were made more publicly — though not always framed as a negative.

It is, of course, not necessarily the case that the IPCC’s tendency to lean toward the more conservative possibility is incorrect. If, for example, the level of fossil-fuel consumption is pushed downward, the worst-case scenarios of warming could be avoided. The BBC report over the weekend followed McGuire’s criticism with the opinions of University of Cambridge professor Mike Hulme.

“Science takes time to mature, and for uncertainties to be properly contextualized,” he said. “I think it is dangerous if people start trying to undermine IPCC reports before they are even published.”

It’s also useful to note that most people don’t get their understanding of the effects of climate change from closely parsing the massive IPCC reports on the predicted effects. What’s at issue here is less the accuracy of the report (though that is at issue) than the point Hulme makes: What danger is there in being overly alarmist on the subject?

In that case, ironically, the IPCC appears to err in favor of the outlier: An extreme position of alarm is the more dangerous path to take.

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