Here’s a forgotten paper that deserves more attention: Idso 1998.
Rather than using an enormously complex global circulation model (or 22) to come up with a figure for climate sensitivity, Sherwood Idso does calculations from eight completely different natural experiments which all arrive at similar figures. In short, he reviewed 20 years of work to arrive at a prediction that if CO2 is doubled we will get 0.4°C of warming at most, and even he admitted, it might be an overestimate. Basically by the time CO2 levels double, he says we ought expect 0 – 0.4°C of warming, after feedbacks are taken into account. Idso started off assuming that the feedbacks were largely positive, but repeatedly found that they were negative.
Idso’s approach was novel. Instead of climate sensitivity to CO2, he estimates the sensitivity of the Earth to any factor. He calls it the “surface air temperature sensitivity factor“. Once something known heats or cools the Earth, how much do the net feedbacks amplify or dampen that initial change? Rather than trying to measure and capture every single feedback and process, and then calculate the end results, Idso finds situations where he can isolate a factor and calculate [...]