Mardi 30 avril 2013, 14:30, salle de l'entresol

Modéliser l'atmosphères de planètes fortement irradiées: comment sauver la terre du runaway greenhouse ?

Because current exoplanets detection methods are biased toward shorter
period orbits, most planets discovered to date have a higher equilibrium
temperature than the Earth. If water is available at the
surface, it could be evaporated, leading to the so-called runaway or moist
greenhouse that determines the inner edge of the traditional habitable
zone.

However, so far, emphasis has been put on 1D radiative convective models,
which cannot well predict the impact of clouds, or the non-linear effect
of spatial inhomogeneities which can dominate in the case of close in
exoplanets for which the rotation rate is synchronized with the orbital
motion.

Using a new "generic" 3D GCM developed at LMD for exoplanet studies,
I will first give new estimates of the critical flux above which runaway greenhouse
is triggered on an ocean-bearing world like the Earth. I will show that clouds have
a stabilizing feedback on the climate and thus push the inner edge of the habitable
zone closer to the star than usually inferred from 1D models.
I will also show how the classical runaway greenhouse can be avoided if water is
present only in limited amount. In particular, we will demonstrate that a bistable
climate regime can exist on these objects.