PNNL

Abstract

We analyzed output from the Geoengineering Model Intercomparison Project (GeoMIP) for the two most "realistic" scenarios which use the Representative Concentration Pathway of 4.5 Wm-2 by 2100 (RCP4.5) as the control run and inject sulfate aerosol precursors into the stratosphere. The first, experiment, G3, aims to balance radiative forcing of RCP4.5 at 2020 levels by injection of sulfate aerosols, and the second, G4, injects 5 Tg SO2 per year. We ask whether geoengineering by injection of sulfate aerosols into the lower stratosphere from the years 2020-2070 is able to prevent the demise of minimum annual sea ice, or slow spring snow cover loss. We show that in all available models, despite geoengineering efforts, September sea ice extents still decrease from 2020 to 2070, although not as quickly as in the Control Run. In two of the five models, total September ice loss occurs before 2060 despite geoengineering. Spring snow extent is increased from 2020 to 2070 compared to the Control Run although there is still a decreasing trend in 3 of 4 models. After the cessation of sulfate aerosol injection in 2070, the climate system rebounds to the warmer RCP4.5 state quickly, and thus any sea ice or snow retention as a result of geoengineering is lost within a decade.