CO2 and water vapor greenhouse effect impacts are not independent climate forcings . A new study affirms the “variance in the radiance in these channels is primarily controlled by…temperature” and “atmospheric absorption is strongly saturated in these [CO2, water vapor] channels”.
It has previously been established that greenhouse gas (water vapor, CO2) forcing “cannot be considered an independent component of the surface energy budget” because “anomalies in the downward longwave flux at the surface primarily arise as a consequence of surface temperature anomalies, rather than being the cause of those anomalies” (Singh and Polvani, 2020, Zeppetello et al., 2019).
Image Source: Singh and Polvani, 2020, Zeppetello et al., 2019
Feldman et al. (2015) admit they had to “construct” model-based spectra to simulate a CO2 signal in their seminal paper purporting to show CO2 changes cause temperature changes. This is because the temperature and water vapor levels primarily determine the overall longwave forcing (clear-sky) trends.
Image Source: Feldman et al., 2015
Now, a new study (Liu et al., 2022) affirms the overall trends in downwelling longwave radiation (DLR) from CO2 and water vapor are determined by temperature.
“In the opaque portions of the CO2 absorption band (centered at 667 cm−1) and H2O absorption band (1300 – 1800 cm−1), the overall radiance trends are caused by radiance change which is due almost entirely to the increases in the near-surface temperature because the atmosphere is already too opaque to reflect any gas concentration changes.”
This effectively means that greenhouse gases and associated impacts cannot be assumed to be the cause of temperature, but the consequence.