Based on 10 year averaging The Hadcrut4 data set,
https://www.metoffice.gov.uk/hadobs...time_series/HadCRUT.4.6.0.0.annual_ns_avg.txt
has increased .89 C since 1850.
For the purposes of temperature anomalies degrees K and degrees C are the same graduations,
but even with .7 C that only leaves .19 C for possible feedbacks to the known warming roughly 70 years earlier.
if your four-to-fivefold amplification from water vapour feedback existed, it has always been there,
so the .2C of warming before 1940 would be subject to those amplification factors,
I think Hansen said that 70% of ECS would be complete in 70 years.
If the amplification factor were fourfold, then that pre 1940 .2 C would be (.2 C X 4)*.7= .56 C.
the difficulty with that number, is there is only .19 C of unknown available,
and we still have not taken off the .308 W·m–2 from the TSI increase (roughly .09 C).