A lower and more constrained estimate of climate sensitivity using updated observations and detailed radiative forcing time series.

The equilibrium climate sensitivity (ECS) is constrained based on observed nearsurface temperature change, changes in ocean heat content (OHC) and detailed radiative forcing (RF) time series from pre-industrial times to 2010 for all main anthropogenic and natural forcing mechanism. The RF time series are linked to the observations of OHC and temperature change through an energy balance model and a stochastic model, using a Bayesian approach to estimate the ECS and other unknown parameters from the data. For the net anthropogenic RF the posterior mean in 2010 is 2.1Wm-2 with a 90% credible interval (C.I.) of 1.3 to 2.8Wm-2, excluding present day total aerosol effects (direct+indirect) stronger than -1.7Wm-2. The posterior mean of the ECS is 1.8 °C with 90%C.I. ranging from 0.9 to 3.2°C which is tighter than most previously published estimates. We find that using 3 OHC data sets simultaneously substantially narrows the range in ECS, while using only one set and similar time periods can produce comparable results as previously published estimates including the heavy tail in the probability function. The use of additional 10 yr of data for global mean temperature change and ocean heat content data narrow the probability density function of the ECS. In addition when data only until year 2000 is used the estimated mean of ECS is 20% higher. Explicitly accounting for internal variability widens the 90%C.I. for the ECS by 60 %, while the mean ECS only becomes slightly higher. [ABSTRACT FROM AUTHOR]