A lower and more constrained estimate of climate sensitivity using updated observations and detailed radiative forcing time series R. B. Skeie^{1}, T. Berntsen^{1,2}, M. Aldrin^{3}, M. Holden^{3}, and G. Myhre^{1} ^{1}Center for International Climate and Environmental Research – Oslo (CICERO), Oslo, Norway ^{2}Department of Geosciences, University of Oslo, Oslo, Norway ^{3}Norwegian Computing Center, Oslo, Norway

Abstract. The equilibrium climate sensitivity (ECS) is constrained based on
observed near-surface 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 2.1 W m^{−2} with a 90%
credible interval (C.I.) of 1.3 to 2.8 W m^{−2}, excluding
present day total aerosol effects (direct + indirect) stronger
than −1.7 W m^{−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.

Citation: Skeie, R. B., Berntsen, T., Aldrin, M., Holden, M., and Myhre, G.: A lower and more constrained estimate of climate sensitivity using updated observations and detailed radiative forcing time series, Earth Syst. Dynam. Discuss., 4, 785-852, doi:10.5194/esdd-4-785-2013, 2013.