Figure 5.

Schematic illustrating the two dynamical routes to glaciation. The parameter space of generalized volcanic outgassing V_g and generalized stellar flux S_g follows the regime plot in figure 1. Changes in carbon cycle fluxes and radiative fluxes can be straightforwardly mapped into this space; for example, an increase in weathering corresponds to a decrease in V_g and an increase in albedo corresponds to a decrease in S_g. Route A is a crossing of the limit cycle boundary due to decreases in V_g and/or S_g. Route B is a transient rate-induced glaciation triggered by sufficiently fast decreases in S_g; this is accessible anywhere in the parameter space. A decrease in V_g which does not cross the limit cycle boundary does not lead to glaciation. (Online version in colour.)