Clouds Increasingly Influence Arctic Sea Surface Temperatures as CO₂ Rises

Abstract

As Arctic sea ice retreats during the melt season, the upper ocean warms in response to atmospheric heat fluxes. Overall, clouds reduce these fluxes in summer, but how the radiative impacts of clouds on ocean warming could change as sea ice declines has not been documented. In global climate model simulations with variable CO2, the timing of sea ice retreat strongly influences the amplitude of cloud‐induced summer cooling at the ocean surface. Under pre‐industrial CO2 concentrations, summer clouds have little direct effect on maximum annual sea surface temperatures (SST). When CO2 concentrations increase, sea ice retreats earlier, allowing more solar radiation to warm the ocean. Clouds can counteract this summer warming by reflecting solar radiation back to space. Consequently, clouds explain up to 13% more variability in maximum annual SST under modern‐day CO2 concentrations. Maximum annual SST are three times more sensitive to summer clouds when CO2 concentrations are four times pre‐industrial levels.

Sensitivities of Vegetation Gross Primary Production to Precipitation Frequency in the Northern Hemisphere from 1982 to 2015

“…However, the rapid warming of the pan-Arctic has led to the melting of sea ice and increased precipitation. Clouds, fog, and water vapor have delayed the rise in surface temperature and hindered the photosynthesis of surface vegetation [67], which may have led to the negative correlation between the frequency of pan-Arctic precipitation and vegetation GPP. This study showed that precipitation in spring and summer did not affect GPP in cropland, possibly due to human activity (such as irrigation) in the primary growth period of crops.…”