Using an atmospheric general circulation model of intermediate complexity coupled to a sea ice – slab ocean model, we perform a number of sensitivity experiments under present-day orbital conditions and geographical distribution to assess the possibility that land albedo, atmospheric CO2, orography and oceanic heat transport may cause an ice-covered Earth. Changing only one boundary or initial condition, the model produces solutions with at least some ice-free oceans in the low latitudes. Using some combination of these forcing parameters, a full Earth's glaciation is obtained. We find that the most significant factor leading to an ice-covered Earth is the high land albedo in combination with initial temperatures set equal to the freezing point. Oceanic heat transport and orography play only a minor role for the climate state. Extremely low concentrations of CO2 also appear to be insufficient to provoke a runaway ice-albedo feedback, but the strong deviations in surface air temperatures in the Northern Hemisphere point to the existence of a strong nonlinearity in the system. Finally, we argue that the initial condition determines whether the system can go into a completely ice covered state, indicating multiple equilibria, a feature known from simple energy balance models.

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runaway icealbedo surface air temperatures icecovered earth orography orbital conditions nonlinearity energy balance freezing ice slab ocean geographical land icefree oceans land albedo atmospheric co2 orography and oceanic heat transport covered atmospheric general circulation model earths glaciation system

G. Lohmann,K. Grosfeld,V. Romanova,.Effect of land albedo, CO2, orography, and oceanic heat transport on extreme climates. 2 (1),.

G. Lohmann,K. Grosfeld,V. Romanova,"Effect of land albedo, CO2, orography, and oceanic heat transport on extreme climates" 2

G. Lohmann,K. Grosfeld,V. Romanova,"Effect of land albedo, CO2, orography, and oceanic heat transport on extreme climates"