[update from a reader 10/23/2021: Message: Regarding the quotation in Kenneth Richards’ Oct 18 article “2001-2019 Warming Driven By Increases In Absorbed Solar Radiation, Not Human Emissions.” While I am a climate skeptic, it worries me to see that the author quotes the Loed, et al report incorrectly. (https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021GL093047)
The full statement in the report is “This trend is primarily due to an increase in absorbed solar radiation associated with decreased reflection by clouds and sea-ice and a decrease in outgoing longwave radiation (OLR) due to increases in trace gases and water vapor.” Richards left out everything after the word “clouds.” CO2 is one of the trace gases, and according to this report, its heat-trapping propensity in the atmosphere is equally important as a cause of global warming as “decreased reflection by clouds.” I also note that there are theoretical connections between decreased cloud cover and increased levels of CO2.~cr]
By Kenneth Richard on 18. October 2021
Three new studies affirm the increase in absorbed solar radiation associated with decreased reflection by clouds (albedo) has been the “root cause” of the positive Earth Energy Imbalance and global warming since the early 2000s.
Scientists (Loeb et al., 2021) have determined the rather uncertain positive trend in Earth’s Energy Imbalance (EEI) from 2005 to 2019, 0.5 W/m² ±0.47 W/m² per decade−1, is “primarily due to an increase in absorbed solar radiation associated with decreased reflection by clouds.”
CERES satellite data indicate clouds and surface albedo account for 89% of the absorbed solar radiation trend in the 21st century, whereas anthropogenic greenhouse gases account for but a tiny fraction of the trends in combined absorbed solar radiation and greenhouse effect forcing (reductions in emitted thermal radiation) during this period.
This very small human emissions/greenhouse gas impact is represented by the red “Other” (“trace gases”) bars in the graph below. In emitted thermal radiation, graph (e) shows the greenhouse gas impact is effectively offset by the cloud influence; both factors are cancelled out by temperature changes. This leaves the increase in absorbed solar radiation shown in graph (d) due to natural variations in clouds and surface albedo (SFC) as the primary driver(s) of top-of-atmosphere (TOA) flux forcing during the last two decades.
Image Source: Loeb et al., 2021
Other scientists (Dübal and Vahrenholt, 2021) have also concluded that the positive TOA net flux (+1.42 W/m²) from increasing downwelling shortwave (SW) facilitated by a drop in cloudiness has been the “major driving effect,” “dominating influence,” and “major heating cause” explaining the 2001-2019 ocean heat content increase (240 ZJ).
The authors note these CERES satellite observations “conflict with the assumption further global warming originates mainly from the LW [longwave] radiation capture caused by greenhouse gases, i.e., a decline in outgoing LW.” In fact, the LW or greenhouse effect impact has been negative; it has contributed a net cooling influence (-1.1 W/m²) over the last two decades.
Image Source: Dübal and Vahrenholt, 2021
The summarizing text from another new study (Ollila, 2021) bluntly asserts the substantial increase in downwelling SW radiation from 2000-2019 demonstrates “there are natural climate drivers that have rapid and significant temperature impacts exceeding the anthropogenic drivers,” and that any temperature increase since 2015-’16 “cannot be due to anthropogenic reasons.”
Image Source: Ollila, 2021
These newer studies affirming the 21st increase in absorbed solar radiation has driven modern warming are further substantiated by a 2020 Nature journal paper (Delgado-Bonal et al., 2020) extending the positive (+3 W/m²) cloud-albedo SW impact back to 1980.