  In our modeling of the long-term carbon cycle we find potential multiple
steady-states in Phanerozoic climates. We include the effects of biotic
enhancement of weathering on land, organic carbon burial, oxidation of reduced
organic carbon in terrestrial sediments and the variation of biotic
productivity with temperature, finding a second stable steady-state appearing
between 20 and 50 oC. The very warm early Triassic climate as well as an
oceanic anoxic event in the late Cretaceous may be the potential candidates for
an upper temperature steady-state. Given our results, the anthropogenic driven
rise of atmospheric carbon dioxide could potentially push the climate into
tipping points to a modestly higher temperature steady-state, instead of
relaxing back to pre-anthropogenic conditions.
