PNNL

Abstract

We analyze simulated sea ice changes in seven different earth system models that have conducted experiment G1 of the Geoengineering Model Intercomparison Project (GeoMIP). The simulated response of balancing abrupt quadrupling of CO2 (abrupt4xCO2 ) with reduced shortwave radiation successfully moderates annually averaged Arctic temperature rise to about 1°C, with modest changes in seasonal sea ice cycle compared with the pre-industrial control simulations (piControl). Changes in summer and autumn sea ice extent are spatially correlated with temperature patterns, but not in winter and spring seasons. However there are changes of 20-30% in sea ice concentration in all seasons, and these will induce changes in atmospheric circulation patterns. In summer and autumn, the models consistently simulate less sea ice relative to pre-industrial simulations in the Beaufort and Russian Seas, and some models show increased sea ice in the Barents/Kara Sea region. Sea ice extent increases in the Greenland Sea, particularly in winter and spring, associated with changed sea-ice drift. Decreased sea ice cover in winter and spring in the Barents Sea is associated with a northeastward extension of the Atlantic cyclone path under G1. In comparison, the abrupt4xCO2 experiment shows almost total sea ice loss in September and strong correlation with regional temperatures in all seasons consistent with open ocean conditions. The tropospheric circulation displays a Pacific North America (PNA) pattern-like anomaly with negative phase in G1-piControl and positive phase under abrupt4xCO2-piControl. This large scale teleconnection may contribute to, or feedback on, the simulated sea ice cover change in winter.