A water-cycle induced planetary scale bifurcation on Earth-like land planets
Due to their limited water inventories land planets are known to exhibit a very dry climate with all water permanently trapped in ice caps at the high latitudes (assuming low obliquity). By contrast, we demonstrate that in the presence of a mechanism that efficiently recycles water from high latitudes back to low latitudes, land planets exhibit an additional climate state, with intense low-latitude precipitation called here ‘Cold and Wet’(CW) state. For perpetual equinox conditions, we find that both the dry state and the CW state are stable below a certain threshold in background soil albedo while above only the CW state is stable. Starting from the dry state an increase in background soil albedo above the threshold initiates an abrupt planetary scale bifurcation to the CW state. This results in a sudden cooling of about 35°C globally which is of the order of the temperature difference between the present-day and the Snowball Earth state. In contrast to the Snowball Earth instability, we find that the abrupt bifurcation in our study is triggered by a combination of cloud and hydrological feedbacks and, a weakening of poleward moisture transport rather than by the snow-albedo feedback.