I dont think it is so much the change. it is more the behaviour. I for one cannot quantify it. One of the IPCC lead authors (Trenberth) was not able to quantify it. However he did say that equilibrium was still decades away. And that would have been based on the latest computer models. CMIP5. How wrong it turned out.
in regards to forcings i believe 1.6 to 1.8 would be fair to say
