A new CO2 climate sensitivity study suggests that, beyond the 300 ppm threshold, “any further increase of (anthropogenic) CO2 cannot lead to an appreciably stronger absorption of radiation, and consequently cannot affect the earth’s climate.”
Dr. Schildknecht is a Bielefeld University physics professor affiliated with the Max Planck Institute in Munich.
His equilibrium climate sensitivity estimate (0.5 or 0.6°C for a doubling of CO2 from 380 to 760 ppm) is identical to many other recent estimates (Stallinga et al., 2020, Ollila, 2019, Smirnov, 2017, Smirnov, 2020, Harde, 2016, Bates, 2016, Kissin, 2015, Abbot and Marohasy, 2017, Gervais, 2016).
“Based on new radiative transfer numerical evaluations, we reconsider an argument presented by Schack in 1972 that says that saturation of the absorption of infrared radiation by carbon dioxide in the atmosphere sets in as soon as the relative concentration of carbon dioxide exceeds a lower limit of approximately 300 ppm. We provide a concise brief and explicit representation of the greenhouse effect of the earth’s atmosphere. We find an equilibrium climate sensitivity (temperature increase ∆T due to doubling of atmospheric CO2 concentration) of ∆T ≃ 0.5°C. We elaborate on the consistency of these results on ∆T with results observationally obtained by satellite-based measurements of short-time radiation-flux versus surface-temperature changes.”
“The absorption reaches values close to 100% for a realistic CO2 content of 0.03%, it is concluded that any further increase of (anthropogenic) CO2 cannot lead to an appreciably stronger absorption of radiation, and consequently cannot affect the earth’s climate.”
“[T]he effect of an anthropogenic CO2 increase on the climate on earth is fairly negligible.”