In yet another new paper (Drotos et al., 2020), scientists determine the climate sensitivity to CO2 is “practically zero” the more the concentration rises. A ~4450 ppm CO2 concentration has cooler climates than observed in the pre-industrial (278 ppm) era. Why? A self-amplifying cloud feedback mechanism cools the Earth by magnitudes “as large as 10 K” upon warming saturation.
Earlier this year, scientists published a paper using mesocosms (controlled outdoor experiments) to demonstrate CO2 concentrations of 3200, 7500, and 16,900 ppm are associated with colder temperatures than in outdoor environments with 480 ppm CO2 concentrations.
Now, in another new paper (Drotos et al., 2020), several more scientists are asserting the Earth system has an internal, self-amplifying negative cloud feedback mechanism so powerful that
“at CO2 concentrations beyond four times the preindustrial value, the climate sensitivity decreases to nearly zero as a result of episodic global cooling events as large as 10 K”.
The cooling events spawned by the high CO2 concentrations lead to temperature “drops below the coldest values of the control [278 ppm pre-industrial CO2]” such that the climate sensitivity to CO2 doublings is “practically zero” over time.
“In particular, the climatological mean value of the global mean surface temperature practically stops responding to an increase in the CO2 concentration. This practically zero climate sensitivity suggests that the effect of a feedback on the global mean surface temperature may turn out to be as strong as the radiative effect of CO2.”
In other words, scientists have found yet another way the claimed “runaway greenhouse” response of the climate system to elevated CO2 turns out to be a false alarm.