Séminaire, par Jérémy Leconte
Mardi 8 avril 2014, 14:30, salle Daniel Chalonge (entresol)
Because the solar luminosity increases over geological timescales, Earth climate is expected to warm, increasing water evaporation which, in turn, enhances the atmospheric greenhouse effect. Above a certain critical insolation, this destabilizing greenhouse feedback can "runaway" until all the oceans are evaporated (the so-called runaway greenhouse instability). Through increases in stratospheric humidity, warming may also cause oceans to escape to space before the runaway greenhouse occurs. The critical insolation thresholds for these processes, however, remain uncertain because they have so far been evaluated with unidimensional models that cannot account for the dynamical and cloud feedback effects that are key stabilizing features of Earth's climate. With more than 1000 exoplanets discovered, the need to understand these processes goes beyond the boundaries of the Earth, as it is the main way to know which planet can harbor liquid water...
Here I will present the generic version of a global climate model that I have been developing specifically to quantify the climate response of terrestrial planets to increased insolation in hot and possibly extremely moist atmospheres. I will also show the application of this model to various extreme planetary climate questions: when will the Earth lose its oceans? How much does this runaway greenhouse limit depend on the spectral type of the star? And what happens when planetary tides have been strong enough to synchronize the rotation of the planet with its orbit, leaving one hemisphere permanently sunlit and the other in eternal darkness?
Extreme planetary climates: when will the Earth lose its oceans, how will other planets keep them?
Because the solar luminosity increases over geological timescales, Earth climate is expected to warm, increasing water evaporation which, in turn, enhances the atmospheric greenhouse effect. Above a certain critical insolation, this destabilizing greenhouse feedback can "runaway" until all the oceans are evaporated (the so-called runaway greenhouse instability). Through increases in stratospheric humidity, warming may also cause oceans to escape to space before the runaway greenhouse occurs. The critical insolation thresholds for these processes, however, remain uncertain because they have so far been evaluated with unidimensional models that cannot account for the dynamical and cloud feedback effects that are key stabilizing features of Earth's climate. With more than 1000 exoplanets discovered, the need to understand these processes goes beyond the boundaries of the Earth, as it is the main way to know which planet can harbor liquid water...
Here I will present the generic version of a global climate model that I have been developing specifically to quantify the climate response of terrestrial planets to increased insolation in hot and possibly extremely moist atmospheres. I will also show the application of this model to various extreme planetary climate questions: when will the Earth lose its oceans? How much does this runaway greenhouse limit depend on the spectral type of the star? And what happens when planetary tides have been strong enough to synchronize the rotation of the planet with its orbit, leaving one hemisphere permanently sunlit and the other in eternal darkness?