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.
[S]hortwave radiation is the main driver in the dynamics and plays a major role in the energy balance by affecting the longwave radiation field.”
“Our research supports the idea that clouds and albedo, which ultimately determine the SW radiation, are variables of the utmost importance for current climate change, in agreement with previous research about the changes in stratocumulus or energy imbalance in the last four decades for example. An increase in cloud coverage of 0.1 would, on average, lead to a 7% increase in spectrally integrated global average reflectance of shortwave radiation.”