An Estimate of Equilibrium Climate Sensitivity From Interannual Variability

Estimating the equilibrium climate sensitivity (ECS; the equilibrium warming in response to a doubling of CO₂) from observations is one of the big problems in climate science. Using observations of interannual climate variations covering the period 2000 to 2017 and a model‐derived relationship between interannual variations and forced climate change, we estimate that ECS is likely 2.4–4.6 K (17–83% confidence interval), with a mode and median value of 2.9 and 3.3 K, respectively. This analysis provides no support for low values of ECS (below 2 K) suggested by other analyses. The main uncertainty in our estimate is not observational uncertainty but rather uncertainty in converting observations of short term, mainly unforced climate variability to an estimate of the response of the climate system to long‐term forced warming.