Patrick Carlberg writes:
I can’t assess the validity of the values from the climate models presented in AR5 (mostly due to lack of time). But I can tell you there are tricks used in the way they interpret the statistical inference.
One of the key points in the new IPCC report is that the CO2 forcing level of confidence was increased from “High” to ”Very High”. The way this was done was by increasing the uncertainty. The means are about the same in AR4 and AR5 but the uncertainty interval has increased from 0.34 to 0.7.
In the same graph (In AR5) an estimate of the total anthropogenic radiative forcing is included. Given the uncertainty in the calculations there is no statistical difference between 1980 and 2011.
My guess is that if the 1950 values were included at the same level of confidence then there wouldn’t be any difference between 1950 and 2011 either.