"… As this paper then illustrates, when energy accumulates in the climate system due to an enhancement in atmospheric greenhouse gas concentrations, this accumulation is primarily due to an increase in absorbed solar radiation, rather than simply being due to an imbalance in the long-wavelength fluxes. However, this doesn’t somehow contradict that adding greenhouse gases to the atmosphere will cause the system to warm, or suggest that changes in clouds are causing most of the warming.
So, although I haven’t work through the Dübal and Vahrenholt paper in detail, the basic result they present seems broadly consistent with what is expected. That they find that most of the warming over the 2001-2020 period was due to a reduction in cloud albedo doesn’t really contradict our understanding of greenhouse warming and doesn’t suggest that most of the warming over this period was due to changes in clouds.
Most of the warming is almost certainly due to the human emission of greenhouse gases into the atmosphere. How clouds then respond to the subsequent warming then leads to most of the accumulated energy being due to an increase in absorbed solar radiation. If anything, as highlighted in the video in this [post (Can the ECS be less than 2 degrees? | …and Then There's Physics), this might actually be suggesting that equilibrium climate sensitivity is well above 2oC, rather than highlighting some major challenge to our understanding of greenhouse warming.
Links:
Outgoing longwave radiation – post I wrote explaining why most of the accumulated energy is due to increased absorded solar radiation.
Global warming due to increasing absorbed solar radiation – paper by Trenberth and Fasullo.
Shortwave and longwave radiative contributions to global warming under increasing CO2– paper by Donohue et al.