Idealized Ocean Albedo Modification Simulations in the Geoengineering Model Intercomparison Project (GeoMIP)

Abstract:

I present preliminary results from the designed simulation G1ocean-albedo in the Geoengineering Model Intercomparison Project (GeoMIP). This simulation seeks to balance the radiative forcing from an instantaneous quadrupling of the CO₂ concentration by an increase in the albedo of the global oceans. This design is a highly idealized representation of marine cloud brightening proposals.

G1ocean-albedo requires an increase in global ocean albedo between 140 and 153%, depending upon the model. Models show that although top of atmosphere net radiative flux remains at 0 under G1ocean-albedo, global mean temperature increases by approximately 0.5 K. This is in contrast to experiment G1, in which solar irradiance was reduced to compensate for the radiative forcing of quadrupled CO₂; in G1, global mean temperature was unchanged for the duration of the simulation.

Similarly to experiment G1, G1ocean-albedo results in a positive temperature anomaly (as compared to the preindustrial control simulation) in high latitudes of approximately 1.0 K and a negative anomaly over the tropical oceans of approximately 0.5 K. Land temperatures are also increased on average by over 1 K. These features are attributed to feedbacks in the high latitudes, as well as changes in the land-ocean contrast. There is a Southward shift in the ITCZ associated with changes in the hemispheric temperature differences.