Objective estimation of the probability density function for climate sensitivity

Abstract

The size and impacts of anthropogenically induced climate change (AICC) strongly depend on the climate sensitivity, Δ T 2x . If Δ T 2x is less than the lower bound given by the Intergovernmental Panel on Climate Change (IPCC), 1.5°C, then AICC may not be a serious problem for humanity. If Δ T 2x is greater than the upper bound given by the IPCC, 4.5°C, then AICC may be one of the most severe problems of the 21st century. Here we use a simple climate/ocean model, the observed near‐surface temperature record, and a bootstrap technique to objectively estimate the probability density function for Δ T 2x . We find that as a result of natural variability and uncertainty in the climatic radiative forcing, the 90% confidence interval for Δ T 2x is 1.0°C to 9.3°C. Consequently, there is a 54% likelihood that Δ T 2x lies outside the IPCC range.