PNNL

Abstract

Marine cloud brightening through sea-salt injection has been proposed as a method of temporarily alleviating some of the impacts of anthropogenic climate change, as part of a set of technologies called geoengineering. We outline here a proposal for three coordinated climate modeling simulations to test aspects of this method, to be conducted under the auspices of the Geoengineering Model Intercomparison Project (GeoMIP). The first, highly idealized, involves a uniform increase in ocean albedo to offset an instantaneous quadrupling of CO2 concentrations from preindustrial levels. Results from a single model show an increased land-ocean temperature gradient, Arctic warming, and large shifts in annual mean precipitation patterns. The Arctic warming cannot be attributed to changes in Arctic sea ice extent or changes in meridional heat flux. The second experiment involves increasing cloud droplet number concentration in all low-level marine clouds to offset some of the radiative forcing of an RCP4.5 scenario. This experiment will test robustness of the effects of geographically heterogeneous radiative flux changes are. The third experiment involves injection of 100 Tg a-1 sea salt into the marine boundary layer between 30°S and 30°N, offsetting some of the radiative forcing of an RCP4.5 scenario. A single model study shows that radiative flux perturbations are largely confined to the latitudes in which injection occurs. In these single model simulations, the direct effect is stronger than the indirect effect. Cloud droplet number concentrations increased by only 9.1 cm-3 in the injection area.