It takes 10 years and 22 ppm for CO2 to amass just 0.2 W/m² in total surface energy flux. In contrast, short-wave cloud radiative forcing fluctuations vary in amplitude by ±300 W/m² within hours.
Earth’s surface energy imbalance is said to have been positive, +0.6 W/m², during the first decade of this century (Stephens et al., 2012). Problematically, the uncertainty in this assumptive estimation is ±17 W/m², which means the imbalance could be anywhere from -16.4 W/m² to +17.6 W/m².
Image Source: Stephens et al., 2012
As Sedlar and colleagues emphasize in a new study, clouds “directly modify the solar and infrared radiation reaching the surface,” and the “net result of these energy fluxes determines the warming and cooling processes at the surface.”
Quantitatively, shortwave cloud forcing modulates Earth’s surface radiative flux in magnitudes that vary by ±300 W/m² and up to 600 W/m².
“As clouds typically attenuate shortwave radiation, CRFSW at the surface is negative, resulting in a relative cloud cooling effect (e.g., Ramanathan et al., 1989). The CRFSW observed for the two low cloud types shows a wide range, from quite strong, −600 W/m², to quite modest near 0 W/m² (Figure 10a). Subsequently, THFs respond to the modification of SWD by the cloud type. Under low stratiform periods, individual scatter points of Hs + Hl were frequently observed between 0 and 300 W/m² and correspond to a median CRFSW (black square within blue scatter) approximately −300 W/m².”
Image Source: Sedlar et al., 2022
Another new study (Padmakumari et al., 2022) suggests the amplitude of shortwave cloud radiative forcing perturbs the surface energy imbalance in magnitudes reaching 1000 W/m².
“CES induced positive shortwave cloud radiative forcing (CRF) varied up to +400 W/m² (warming effect), while negative CRF varied up to −1000 W/m² (cooling effect).”
Image Source: Padmakumari et al., 2022
Meanwhile, it takes about 22 ppm of CO2 concentration changes to impact Earth’s surface energy budget by a grand total of 0.2 W/m² (Feldman et al., 2015). Extrapolated, it would take a 110 ppm CO2 concentration change to affect the surface energy imbalance by 1 W/m².
Image Source: Feldman et al., 2015
For advocates of the position that CO2 is the primary driver of changes to Earth’s highly uncertain surface energy imbalance (and, therefore, climate change), it must be assumed that cloud properties remain static over time, allowing cloud shortwave radiative effects to perpetually cancel out to zero over decades and centuries.
Given the shortwave cloud radiative forcing magnitudes identified in the scientific literature, this assumption is extremely unrealistic.