Cloud albedo changes in response to anthropogenic sulfate and non-sulfate aerosol forcings in CMIP5 models

Abstract

Abstract. The effects of different aerosol types on cloud albedo are analysed using the linear relation between total albedo and cloud fraction found on a monthly mean scale in regions of subtropical marine stratocumulus clouds and the influence of simulated aerosol variations on this relation. Model experiments from the Coupled Model Intercomparison Project phase 5 (CMIP5) are used to separately study the responses to increases in sulfate, non-sulfate and all anthropogenic aerosols. A cloud brightening on the month-tomonth scale due to variability in the background aerosol is found to dominate even in the cases where anthropogenic aerosols are added. The aerosol composition is of importance for this cloud brightening, that is thereby region dependent. There is indication that absorbing aerosols to some extent counteract the cloud brightening but scene darkening with increasing aerosol burden is generally not supported, even in regions where absorbing aerosols dominate. Month-to-month cloud albedo variability also confirms the importance of liquid water content for cloud albedo. Regional, monthly mean cloud albedo is found to increase with the addition of anthropogenic aerosols and more so with sulfate than non-sulfate. Changes in cloud albedo between experiments are related to changes in cloud water content as well as droplet size distribution changes, so that models with large increases in liquid water path and/or cloud droplet number show large cloud albedo increases with increasing aerosol. However, no clear relation between model sensitivities to aerosol variations on the month-to-month scale and changes in cloud albedo due to changed aerosol burden is found.

Assessment of aerosol–cloud–radiation correlations in satellite observations, climate models and reanalysis

“…4, and show some interesting differences from the observational correlations. Contrary to the satellite observations and the findings by Bender et al (2016) and Frey et al (2017), R(L, cloud ) is not significantly positive in any of the ten regions, but actually negative for Iceland, Vanuatu, China, Peruvian and Namibian. R(L, f c ) is also in contrast with observations negative for all regions.…”

“…The importance of L for cloud in Sc regions, discussed e.g. by Bender et al (2016) and Frey et al (2017), is confirmed by positive correlations R(L, cloud ) in all five Sc regions. R(L, cloud ) is further positive for all regions except with L MAC in the US region.…”

“…The Canarian region, shows the greatest a and a variability, related to the dominance of desert dust and the a is also high in the Namibian region, that has a comparatively strong signal of black carbon from biomass burning (cf. Frey et al (2017)). The anthropogenically influenced regions (US, China) have distinctively larger N d than the other regions.…”

Ozone—climate interactions and effects on solar ultraviolet radiation

“…Model results have shown large increases in the albedo of clouds with increasing concentration of aerosols which are related to changes in the water content of clouds and in the size distribution of cloud droplets. 125 With respect to the origin of aerosols, anthropogenic sulfate aerosols had greater effect on albedo of clouds than non-sulfate aerosols.…”

The evolution of cloud microphysics upon aerosol interaction at the summit of Mt. Tai, China

“…Through Model experiments with the Coupled Model Intercomparison Project phase 5 (CMIP5), Frey et al (2017) found that the monthly mean cloud albedo of subtropical marine stratocumulus clouds increased with the addition of anthropogenic aerosols.…”