Recent estimates of low climate sensitivity were flawed

An atmospheric model simulation showing various types of aerosol particles. White marks sulfate aerosols from volcanoes and fossil fuel emissions. Red is dust, green is smoke, and blue is sea salt.

William Putman, NASA/Goddard

Earth’s climate system is a complex beast. In order to discuss it, we often rely on simple measures like climate sensitivity—an estimate of how much warming we can expect to get from a given increase in greenhouse gas concentrations. Unfortunately, measuring the climate sensitivity isn’t that simple. Among other complications, you have to pick the timeframe you’re interested in. The climate system is sluggish in some ways, so the longer you give it to respond, the greater its response will be.

A few recent studies generated some hub-bub (partly through a popular article in The Economist) by coming up with low values for climate sensitivity based on analyzing the observed temperature change of the last few decades. Opponents of the scientific consensus on climate change seized on this to argue that carbon dioxide’s impact is small and projections of future change are exaggerated.

Apart from the danger of reading too much into the slower surface warming of the last decade (which appears to mostly be the result of natural variability) this thinking suffers from another problem: those low values appear to be wrong.