1. Fig. 1 Generic bifurcation diagram illustrating the Snowball Earth hysteresis.
Generic bifurcation diagram illustrating the Snowball Earth hysteresis. Ice-line latitude as a function of solar or CO2 radiative forcing in a one-dimensional (1D) (meridional) energy-balance model of the Budyko-Sellers type (3, 4), showing three stable branches (red, green, and blue solid lines) and the unstable regime (dashed line). Yellow dots are stable climates possible with present-day forcing. Black arrows indicate nonequilibrium transitions. In response to lower forcing, ice line migrates equatorward to the ice-albedo instability threshold (a), whereupon the ice line advances uncontrollably to the equator (Eq) (b). With reduced sinks for carbon, normal volcanic outgassing drives atmospheric CO2 higher over millions to tens of millions of years (73) until it reaches the deglaciation threshold (c). Once the tropical ocean begins to open, ice-albedo feedback drives the ice line rapidly poleward (in ~2 ky) (327) to (d), where high CO2 combined with low surface albedo creates a torrid greenhouse climate. Intense silicate weathering and carbon burial lower atmospheric CO2 (in 107 years) (164) to (e), the threshold for the reestablishment of a polar ice cap. The hysteresis loop predicts that Snowball glaciations were long-lived (b and c), began synchronously at low latitudes (a and b), and ended synchronously at all latitudes under extreme CO2 radiative forcing (c and d). The ocean is predicted to undergo severe acidification and deacidification in response to the CO2 hysteresis. Qualitatively similar hysteresis is found in 3D general circulation models (GCMs). Pco2, partial pressure of CO2; wrt, with respect to.
Paul F. Hoffman et al. Sci Adv 2017;3:e
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