Calculating Sensitivity from the LGM
Despite the common misconception that estimates for equilibrium climate sensitivity (ECS) are only derived from model simulations (sometimes erroneously said to be model inputs), there are many ways to estimate ECS. Here on this blog, I've used the energy balance equation with empirical data, and despite varying levels of complexity in quantifying forcings, I keep coming up with a value for ECS of ~3.2°C for 2xCO2 . I consider these back-of-the-envelope calculations, fitting for a blogpost to show IPCC estimates are plausible and realistic, but not really for much else. All these types of equations cover a relatively short time period (~175 years) and can be significantly impacted by the uncertainties in the relevant forcings, most importantly aerosols. Some recent evidence suggests that scientists may be underestimating the cooling effect of aerosol pollution and thus underestimating ECS. In fact, Hansen published a paper recently suggesting that ECS could be as high as 4.8°C.[1] ...