  Cycling of carbon dioxide between the atmosphere and interior of rocky
planets can stabilize global climate and enable planetary surface temperatures
above freezing over geologic time. However, variations in global carbon budget
and unstable feedback cycles between planetary sub-systems may destabilize the
climate of rocky exoplanets toward regimes unknown in the Solar System. Here,
we perform clear-sky atmospheric radiative transfer and surface weathering
simulations to probe the stability of climate equilibria for rocky,
ocean-bearing exoplanets at instellations relevant for planetary systems in the
outer regions of the circumstellar habitable zone. Our simulations suggest that
planets orbiting G- and F-type stars (but not M-type stars) may display
bistability between an Earth-like climate state with efficient carbon
sequestration and an alternative stable climate equilibrium where CO$_2$
condenses at the surface and forms a blanket of either clathrate hydrate or
liquid CO$_2$. At increasing instellation and with ineffective weathering, the
latter state oscillates between cool, surface CO$_2$-condensing and hot,
non-condensing climates. CO$_2$ bistable climates may emerge early in planetary
history and remain stable for billions of years. The carbon dioxide-condensing
climates follow an opposite trend in $p$CO$_2$ versus instellation compared to
the weathering-stabilized planet population, suggesting the possibility of
observational discrimination between these distinct climate categories.
