Effect of land albedo, CO₂, orography, and oceanic heat transport on extreme climates

V. Romanova (1) , G. Lohmann (2, 3) , K. Grosfeld (2, 3)

1 Institute of Oceanography
2 Department of Bentho-pelagic processes
3 Department of Physics [Bremen]

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.

Domaines: Interfaces continentales, environnement; Sciences de la Terre

V. Romanova, G. Lohmann, K. Grosfeld. Effect of land albedo, CO₂, orography, and oceanic heat transport on extreme climates. Climate of the Past, 2006, 2 (1), pp.31-42. ⟨hal-00298045⟩