A new study finds the modeling-based claim that cloud cover changes are only responding to anthropogenic CO2 forcing as a feedback – and not functioning independently as a forcing – has (again) been contradicted by observations.
Since this is a water planet, and since clouds are formed when water vapor turns into water droplets, it is a tad disconcerting we are now being warned by the “expert” class that clouds may “disappear forever” as the Earth warms.
Image Source: indiatimes.com
Of course, even a casual observation of the seasonal cloud cover variations affirms that clouds increase in Arctic summer (warmer) and decrease in winter (cooler).
“Winter cloud occurrence…was 70%. It increased to over 80% the summer months and reached a 95% peak in September” (Maillard et al., 2021).
Image Source: Maillard et al., 2021
Further, a decline in cloud cover means more solar radiation is absorbed by the surface, leading to a net positive forcing (warming) because the shortwave effects of cloud albedo modulation exceed the longwave effects of clouds.
For example (staying with the Arctic), the increase in shortwave forcing associated with the decline in cloud cover in recent decades amounted to +7.3 W/m² positive imbalance from 1994-2017 over the Greenland ice sheet (Hahn et al., 2020). This is the dominant reason for the Greenland ice sheet melt over this period.
Image Source: Hahn et al., 2020
Now, another new study shows cloud cover clearly declined globally from 1983-2017. The mechanism driving the change in cloud cover is unknown, but other scientists have chalked it up to “internal unforced variability“.
The nearly 4 decades of falling cloud cover resulted in a net positive radiative forcing, heavily contributing to global warming over this period.
In contrast, IPCC climate models claim clouds only respond to (positive feedback) CO2 rise, or warming. But, as noted, the opposite occurs in observations: clouds increase as it warms, and increasing clouds leads to (net) cooling.
Therefore, the data clearly show “the cloud cover decrease could not have been caused by the increased surface temperature…and was not caused directly or indirectly by CO2” (Jonas, 2022).
So the models are wrong. Cloud feedback is negative. CO2 doesn’t cause the cloud changes, and thus an increase in shortwave forcing associated with a decline in cloud cover also occurs independently of CO2 or human influences. Consequently, “climate models and the IPCC over-estimate the effect of the atmospheric CO2 change.”