A groundbreaking British study throws cold water on the U.N.’s most extreme climate-change scenarios, finding little chance that the planet will heat up by 4 to 5 degrees over the next century.
The UN International Panel on Climate Change has predicted for 25 years that global temperatures are likely to increase between 1.5 and 4.5 degrees Celsius by 2100, but the latest research narrows the range to 2.2-3.4 degrees Celsius.
“Our study all but rules out very low and very high climate sensitivities, so we now know much better what we need to,” said University of Exeter professor Peter M. Cox, the lead author of the study, in a press release.
The study, published Thursday in the journal Nature, calculates equilibrium climate sensitivity [ECS] using “the variability of temperature about long-term historical warming, rather than on the warming trend itself,” according to the abstract.
The approach produced a central estimate of an increase of 2.8 degrees Celsius with a 66 percent confidence level, lowering the standard uncertainty in climate sensitivity by about 60 percent.
University of Leeds professor Piers Forster lauded the paper for its “ingenious approach to rule out high estimates,” calling it “the first convincing evidence that we are not living in a world in which ECS is greater than the range of values thought likely by the IPCC.”
“The idea underpinning this work is so enviably simple that it will make climate scientists ask, ‘Why didn’t I think of that?’” said Mr. Forster in a companion article in Nature.
The study’s conclusions about ECS, defined as the global warming that would occur if carbon dioxide levels in the atmosphere were instantly doubled, also improve the chances of meeting the goals of the Paris climate accord.
“If the upper limit of ECS can truly be constrained to a lower value than is currently expected, then the risk of very high surface-temperature changes occurring in the future will decrease,” said Mr. Forster. “This, in turn, would improve the chances of keeping the temperature increase well below 2 °C above pre-industrial levels.”
The research also has implications for the climate-change movement, said University of Colorado Boulder professor Roger A. Pielke Jr.
“If your climate advocacy is grounded in ‘[it’s] gonna be bad, really bad’ arguments, then new science (‘not as bad’) puts you in an awkward position,” he said on Twitter. “No doubt some catastrophists will today feel a need to diss the new study lest they give evil deniers due.”
Mr. Cox, a professor of climate system dynamics, was a lead author of Chapter 7 of the IPCC’s fourth assessment report on climate change.
“Climate sensitivity is high enough to demand action, but not so high that it is too late to avoid dangerous global climate change,” said Mr. Cox in the release, which was reprinted on the climate website Watts Up With That.