Present-day and ice-covered equilibrium states in a comprehensive climate model


We show that in a comprehensive climate model both the current climate and a completely ice-covered Earth are stable states under today's total solar irradiance (TSI) and CO2 level. We employ the Max Planck Institute for Meteorology coupled atmosphere-ocean general circulation model ECHAM5/MPI-OM, at relatively high resolution (horizontally T63 in the atmosphere and 1.5 degrees in the ocean). Setting TSI to near-zero causes a transition from realistic present-day climate to a completely ice-covered state within 15 years; this state persists even when TSI re-assumes today's value. A break-up of the complete ice cover occurs with today's TSI and 100 times – but not with 10 times – today's atmospheric CO2 level. While TSI is near-zero, extremely strong meridional overturning ensues in both the Atlantic and the Pacific Oceans. Our results imply that a snowball Earth is possible, in principle, with inception possibly triggered by a brief dark spell

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