Runaway Cooling From Large Solar Reductions Modulated by Ocean Overturning Circulation and Heat Uptake

The climate system can respond asymmetrically to warming and cooling, yet this asymmetry remains underexplored. This study uses multi-century experiments with two coupled global climate models under idealized abrupt solar forcing changes of (Formula presented.) 1%, 2%, 4%, and 6%. In both models, cooling has a larger impact on surface temperature than warming, driven by the ice-albedo feedback. However, under strong cooling (−4%, −6% Solar), the models diverge significantly. One model undergoes runaway ice growth, while the other has slower ice expansion and even transient sea ice retreat in the north Pacific. The latter is linked to the development of a strong Pacific meridional overturning circulation, which transports heat northward and slows ice growth. The model with less ice growth also exhibits greater “cold uptake into” (or heat release from) the deep ocean. These findings motivate further investigation of inter-model differences in ocean-ice-atmosphere interactions and their impacts on climate feedbacks.