The transformation of Arctic clouds with warming

Abstract

The progressive loss of Arctic sea ice leads to increased surface emissions of Dimethyl Sulphide (DMS), which is the dominant local source of sulphate aerosols. We test the hypothesis that cloud condensation nuclei, derived from DMS, will increase cloud-top albedo in an earth-system global climate model. The earth-system model includes fully interactive ocean biology, DMS, atmospheric chemistry, aerosols and cloud microphysics. In an idealised warming scenario, the Arctic Ocean becomes ice-free in summer when atmospheric CO2 is increased by 1 % per year to four times the pre-industrial concentrations. The summer boundary layer near-surface inversion strengthens, increasing stratification with warming, whilst the autumn inversion weakens. We find that the dominant change in cloud albedo arises from the conversion of summer clouds from ice to liquid, reducing the solar flux at the surface by 27 W m−2. Only 1–2 W m−2 of the reduced solar flux is attributed to cloud condensation nuclei associated with sulphate aerosols derived from the 2–5 fold increase in DMS emissions that results from an ice-free ocean. We conclude that aerosol-cloud feedbacks originating from DMS production in the Arctic region are largely mitigated through increased wet deposition of sulphate aerosols by rainfall and as a result are not a significant component of changes in the surface radiation budget in our model.