A new study by a team of climatologists "all but rules out" the worst-case "doomsday" U.N. climate change scenarios, significantly narrowing the range of the possible temperature increases, while also eliminating the low-end predictions. The study's findings, said one leading expert, are "reassuring," though scientists still warn that potentially "significant" changes are coming.
"Our study all but rules out very low and very high climate sensitivities," University of Exeter's Peter Cox, the study's lead author, said.
The U.N.'s worst-case predictions of an increase of 4.5 degrees Celsius by 2100 are almost certainly too high, Cox and his colleagues found. Rather than the widely variable range of 1.5 - 4.5 ºC (2.7 - 8.1 ºF) promoted by the U.N.'s Intergovernmental Panel on Climate Change (IPCC), the new study predicts much narrower change ranges of 2.2 - 3.4 ºC (4 - 6.1 ºF). The study's best estimate is that global temperatures will change by 2.8 ºC (5 ºF) by 2100.
"If accurate, it precludes the most destructive doomsday scenarios," AFP notes. The outlet cites two experts that welcome the results of the "more accurate estimate":
"These scientists have produced a more accurate estimate of how the planet will respond to increasing CO2 levels," said Piers Forster, director of the Priestley International Centre for Climate at the University of Leeds.
Gabi Hegerl, a climate scientist at the University of Edinburgh who, like Forster, did not take part in the research, added: "Having lower probability for very high sensitivity is reassuring. Very high sensitivity would have made it extremely hard to limit climate change according to the Paris targets."
Scientists admit that attempting to determine the "known unknown" of "equilibrium climate sensitivity" requires accounting for a wide range of notoriously difficult-to-predict factors, including, as Cox notes, the climate "tipping points," rapid changes in the climate that have occurred historically caused by the planet itself rather than more predictable external factors.
As MIT atmospheric physician Richard Lindzen explains in the video below, all the variables, or "known unknowns," make accurate predictions about the climate "impossible" — a reality the IPCC admitted in its 2007 report, which stated, "The long-term prediction of future climate states is not possible." Here's Lindzen discussing the science (and politics) behind climate change models: