The radiative forcing value of aerosols and clouds in the AR6

This is my proposal for the report of U.S. Department of Energy by the name "A Critical Review of Impacts of Greenhouse Gas Emissions on the U.S. Climate"

Addition to 3.1.1

According to Fig. 3.1.2, which is a copy from Fig. 7.6 of the AR6, the ’The sum of the 'Aerosols, clouds and contrails' is -1,00 Wm^-2 in 2019. The same figure in the AR5 was -0.82 Wm^-2. It means that according to the IPCC science, the RF effect of clouds and aerosols has cooled the atmosphere by the RF value of 0.18 Wm^-2. This conflicts with the CERES observations, which show that the Absorbed Solar Radiation (ASR) due to decreased albedo has increased from 2011 to 2019 by 1.29 Wm^-2 (Ollila, 2024).

The temperature impact of the RF values can be estimated by comparing the data in Figures 7.6 and 7.7 of the AR6. The total RF in 2019 was 2.70 Wm^-2, and its temperature impact was 1.27 ºC. It means that using the IPCC’s simple climate model approach, the climate sensitivity parameter (CSP) is 0.47 K/(Wm^-2). It is a little bit smaller than the CSP value of 0.5 K/(Wm^-2) reported in previous Assessment Reports of the IPCC. By applying this CSP value, the ASR temperature effect would be for about 0.6 ºC (Ollila, 2024). If the whole impact of the observed ASR increased from 2001 to 2019 would be considered, the calculated temperature for the period 1750-2019 according to the IPCC science would be about 2.0 ºC.

Even though the IPCC has recognised the increased ASR trend in Figure 7.3 of the AR6, they have omitted this impact totally in the RF and temperature calculations presented in Figures 7.6 and 7.7. Probably the reason is the far too large impact of the ASR increase on the temperature according to the computer models, which apply the positive water feedback. In reality, the ASR change increased the real temperature from 2011 to 2019 by about 0.34 ºC, which was the main driver to increase the observed temperature of 0.85 ºC in 2011 to the observed temperature of 1.27 ºC in 2019 (Ollila, 2024).

References

Ollila, A. (2024). The 2023 record temperatures: correlation to absorbed shortwave radiation anomaly 

Science of Climate Change, Vol. 4.1. https://doi.org/10.53234/scc202403/15