This is very far from the same thing as projected temperature change between today and 2100. (cato-unbound.org)
Projected temperature changes over this century are too small to breach the latter two conditions. (link.springer.com)
If so, then the Stefan - Boltzmann equation applied to the observed temperature change (and projected temperature change under double CO2) should approximately tell you the total forcing incorporating climate system feedbacks? (realclimate.org)