Figure 7.

Forcing the model with step decreases of V (volcanic outgassing) that persist for different time periods. S = 1280 W m⁻². The dashed line indicates the position of the limit cycle bifurcation. Recall that anomalous increases in weathering are functionally equivalent to decreases in V. Since changes in carbon fluxes can only initiate glaciation via passage into the limit cycle regime (figure 5), the only perturbation that can create a single transient glaciation event is one that decays before one period of the limit cycle has elapsed (a). Otherwise, multiple iterations of the limit cycle result: after a short-lived post-deglaciation hothouse, glaciation ensues again (b).