I am not, I cited NASA's GISS for the data.
NASA GISS: Science Briefs: Taking the Measure of the Greenhouse Effect
The logic is simple, all the past doubling s of CO2 from ~ 1ppm to 280 ppm, have had a fully equalized
warming of roughly .825°C per doubling step, why should we expect the current doubling step to be any different?
Let's look at the GISS's data another way, from the energy imbalance standpoint.
Total energy imbalance is listed at 150 W/m2, 20% of that is from CO2, or 30 W/m2.
Divide that 30 W/m2 by the 8 doubling steps and we get a value for each doubling step of 3.75 W/m2.
Let's use the ACS formula for CO2 forcing to see how close that number is to their doubling number?
Climate Sensitivity - American Chemical Society
The ACS gives an example of ΔFCO2 = (5.35 W·m–2) ln(265/185) = 1.9 W·m–2, but we just need the level for doubling CO2,
so 5.35 X ln(2)=3.708 W/m2, this is well within the margin of error for these type of measurements.
An analogy would be, do you have to be a mechanical Engineer to know if the car you purchased
with a stated MPG of 40, is actually performing close to that number?