This is basically a modified version of some earlier tweets.
Let me see whether I can delineate the “Aerosol forcing too high” thus “models too hot” argument:
If Nic Lewis’ value/range for aerosol forcing is correct then HadCM3 appears to be incompatible with observationally constraint estimates (see Figure B.1 in this pdf). These inferences are made from Harris et al.’s (2013) PPE results. That is HadCM3 is very unlikely to have a low climate sensitivity for such (low) values of aerosol forcing.
Therefrom it is concluded that models generally are likely to run too hot.
Is that about correct?