Quantifying Changes in the Arctic Shortwave Cloud Radiative Effects.

The shortwave cloud radiative effect (SWCRE) is important for the Arctic surface radiation budget and is a major source of inter‐model spread in simulating Arctic climate. To better understand the individual contributions of various radiative processes to changes in SWCRE, we extend the existing Approximate Partial Radiative Perturbation (APRP) method by adding the absorptivity for the upward beam, considering differences in reflectivity between upward and downward beams, and analyzing the cloud masking effect resulting from changes in surface albedo. Using data from CMIP model experiments, the study decomposes the SWCRE over the Arctic surface and analyzes inter‐model differences in quadrupled CO2 simulations. The study accounts for the influence of surface albedo, cloud amount, and cloud microphysics in the response of SWCRE to Arctic warming. In the sunlit season, CMIP models exhibit a strong, negative SWCRE with a large inter‐model spread. Arctic clouds dampen the surface albedo feedback by reflecting incoming solar radiation and further decrease the shortwave radiation reflected by surface, a fraction of which is scattered back to the surface by clouds. Specifically, this accounts for the majority of the inter‐model spread in SWCRE. In addition, increased (decreased) cloud amount and cloud liquid water reduce (increase) incoming shortwave fluxes at the surface, but they are found to be not critical to the Arctic surface radiation budget and its inter‐model variation. Overall, the extended APRP method offers a useful tool for analyzing the complex interactions between clouds and radiative processes, accurately decomposes the individual SWCRE responses at the Arctic surface. Plain Language Summary: Clouds have a significant impact on how much sunlight reaches the Arctic surface. Here, we refine the method for decomposing sunlight changes into contributions from the variations in surface albedo, cloud amount, and other properties of clouds. The refined method is applied to various climate models in which carbon dioxide is abruptly quadrupled, trying to understand the inter‐model differences in the cloud‐sunlight interaction over the Arctic surface. In the sunlit season, the decrease in surface albedo due to melting sea ice is directly linked to the sunlight reduction by cloud, explaining notable inter‐model differences in total sunlight mediated by the cloud. Cloud reflection reduces incoming solar radiation, thereby mitigating the influence of surface albedo with less solar radiation reaching the surface. Also, clouds reflect less shortwave radiation from the surface due to decreased surface albedo. Changes in cloud amount and liquid water, while affecting incoming shortwave fluxes, are not found to be critical to the changes in the Arctic surface radiation budget produced by climate models. Overall, the refined method proves useful for breaking down the complex interactions between clouds and sunlight. It is a practical tool for understanding individual components of cloud‐sunlight interaction at the Arctic surface. Key Points: A SW radiative decomposition estimates how albedo, cloud fraction, and cloud reflectivity drive responses in SWCRE to increases in CO2Changes in surface albedo mostly determine the magnitude and the inter‐model spread of SWCRE changes observed in the CMIP modelsChanges in cloud fraction and reflectivity in CMIP models show minimal impact on the changes in shortwave cloud radiative effect [ABSTRACT FROM AUTHOR]