Several more estimates of extremely low CO2 climate sensitivity have been added to the database in the last year.
The collection of scientific papers that assess a very low (under 1°C for a doubling of CO2) or a non-quantified, but negligible climate sensitivity has swelled to over 130. In 2015, when it was first published, there were only 50 papers on the list.
Here is the link to the database: 130+ Extremely Low CO2 Climate Sensitivity Papers
Over the years Dr. Boris Smirnov, physicist, has published nearly two dozen books on molecular, atomic, and gas physics.
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In 2020, Smirnov contributed both a scientific paper and Springer book on the physics of climate to the list. In both publications he concludes the equilibrium climate sensitivity (ECS) for a doubling of CO2 (280 to 560 ppm) is just 0.6°C.
Interestingly, he assesses the water molecules and droplets (gas and clouds) – 85% of the infrared radiation flux – serve to reduce rather than enhance the total net forcing from CO2 with feedbacks (1.3 W/m²) via their spectral interaction. He asserts the IPCC has been “wrong” to “ignore this information and give this wrong result” for the role of CO2 molecules in climate change and that the “basis of the Paris climate agreements is wrong”.
Smirnov, 2020 (2XCO2= 0.6°C)
“It is of interest to compare the energetic balance of the Earth with that as a result of human activity. The contemporary released power as a result of human activity is about 2 × 1013 W or to the average energy flux of 0.04 W/m2 that is approximately four orders of magnitude below the solar energy flux penetrating in the Earth’s atmosphere. … Let us define the Equilibrium Climate Sensivity (ECS), that is, the change of the global temperature as a result of the doubling of the concentration of CO2 molecules. This quantity may be used as a characteristic of the influence of the atmospheric composition on the global temperature. On the basis of data of Table 6.1, one can obtain for this value  ECS = (0.6 ± 0.3) °C.”
Smirnov, 2020 (2XCO2 = 0.6°C)
“The contribution to the total radiative flux for the real (standard) atmosphere is 51% due to water molecules, 29% due to water microdroplets (clouds), 18% due to CO2 molecules, and 2% due to CH4 and N2O molecules. In addition, 98% of the flux of infrared radiation at wavelengths below 12.5 µm is created by H2O and CO2 molecules, whereas 85% of the radiative flux at wavelengths above 12.5 µm is due to clouds. If the concentration of atmospheric CO2 molecules is doubled without a change the other atmospheric param-eters, the change of the radiative flux to the Earth due to CO2 molecules is 7.2 W/m2, whereas the change of the total radiative flux with accounting for screening fluxes from other components is 1.3 W/m2 that corresponds to the global temperature change of 0.6 ± 0.3 K. Usually climatological models do not account for the interaction between greenhouse that leads components to a six times larger temperature change. One can compare the latter value with results of NASA programs for the analysis of evolution of the carbon dioxide concentration and the global temperature. From this it follows that doubling of the concentration of atmospheric CO2 molecules is accompanied by the change of the global temperature according to (14). Thus, in the real atmosphere only a forth part of the global temperature change occurs due to variation of the concentration of CO2 molecules results from the greenhouse effect involving these molecules.”