In the linked Real Climate article, Michael E. Mann and Gavin Schmidt, discuss the Sherwood et al 2014 paper on climate sensitivity. The attached image (see caption below) indicates that the effective ECS that Sherwood et al 2014 discuss is in the range of 4 C; however, as the following extract indicates the true ECS is about 10% higher than the value Sherwood et al 2014 present; which implies that the true ECS is likely in the range of 4.4 C.
http://www.realclimate.org/index.php/archives/2014/01/a-bit-more-sensitive/Sherwood, S.C., Bony, S. and Dufresne, J.-L., (2014) "Spread in model climate sensitivity traced to atmospheric convective mixing", Nature; Volume: 505, pp 37–42, doi:10.1038/nature12829
Extracts: "First, ECS is the long term (multi-century) equilibrium response to a doubling of CO2 in an coupled ocean-atmosphere model. It doesn’t include many feedbacks associated with ‘slow’ processes (such as ice sheets, or vegetation, or the carbon cycle). See our earlier discussion for different definitions. Second, Sherwood et al are using a particular estimate of the ‘effective’ ECS in their analysis of the CMIP5 models. This estimate follows from the method used in Andrews et al (2011), but is subtly different than the ‘true’ ECS, since it uses a linear extrapolation from a relatively short period in the abrupt 4xCO2 experiments. In the case of the GISS models, the effective ECS is about 10% smaller than the ‘true’ value, however this distinction should not really affect their conclusions."
Caption: "Figure (derived from Sherwood et al, fig. 5c) showing the relationship between the models’ estimate of Lower Tropospheric Mixing (LTMI) and sensitivity, along with estimates of the same metric from radiosondes and the MERRA and ERA-Interim reanalyses."
