A new analysis by Drs. Wijngaarden and Happer (2020) suggests the “self-interference” saturation of all greenhouse gases in the current atmosphere substantially reduces their climate forcing power.
At the current concentrations, the forcing power for greenhouse gases like CO2 (~400 ppm) and CH4 (1.8 ppm) are already saturated. Therefore, even doubling the current greenhouse gas concentrations may only increase their forcings “by a few percent” in the parts of the atmosphere where there are no clouds. When clouds are present, the influence of greenhouse gases is even further minimized.
While the “consensus” model view is that doubling CO2 from 280 ppm to 560 ppm results in a surface forcing of 3.7 W/m², Wijngaarden and Happer find doubling CO2 concentrations from 400 to 800 ppm increases climate forcing by 3 W/m². This warms the surface by 1.4 K as it “hypothetically” cools the upper atmosphere by 10 K.
Equilibrium climate sensitivity (when positive feedback with water vapor is included) is identified as 2.2 K, which is within 10% of multiple other analyses.