“Radiative” or “rapid” adjustments refer to the response of the climate system to an instantaneous radiative forcing, independent of surface temperature changes. These adjustments occur over timescales from hours (e.g. aerosol–cloud interactions) to months (e.g. stratospheric temperature changes), often overlapping with feedback mechanisms – making their separation in realistic scenarios challenging. Controlled simulation experiments can thus help isolate adjustment processes and improve understanding relevant to more complex cases like volcanic eruptions or ongoing climate change.

The abrupt-solm4p experiment of the Cloud Feedback Model Intercomparison Project (CFMIP), part of the 6th Coupled Model Intercomparison Project (CMIP6), simulates an instantaneous 4 % reduction in the solar constant from a pre-industrial state on 1 January 1850. This study analyses changes in climate variables, cloud properties, and radiative fluxes across different timescales (hours, days, months and up to 150 years) to identify adjustment mechanisms and characteristic fingerprints for a shortwave forcing scenario.

The four participating models show rapid adjustments of $\mathrm{3.57}\pm \mathrm{0.46}\mathrm{W}{\mathrm{m}}^{-\mathrm{2}}$, offsetting ∼ 35 % of the initial forcing. Distinct local patterns include initial rapid surface cooling – especially over Antarctica and the Southern Hemisphere. Stratospheric cooling slows the polar night jet, disrupts the polar vortex, and increases Arctic cloud cover, causing local warming. Within the first month, the troposphere cools more quickly than the ocean surface, decreasing vertical stability and enhancing cloud cover over oceans, while tropical land regions show the opposite change. On monthly timescales, high clouds shift downward due to reduced convective heating.