Evidence for Radiative‐Convective Bistability in Tropical Atmospheres

Earth's energy balance requires that energy absorbed and emitted at the top of the atmosphere be equal; to first order this balance is maintained via the Planck feedback: outgoing longwave radiation increases as surface temperature increases. Failure of the Planck feedback to stabilize the climate is described by three generally independent phenomena: the super‐greenhouse effect, the runaway greenhouse, and multiple equilibria of radiative‐convective atmospheres. Here we use satellite observations and models to show that the existence of the super‐greenhouse gives rise to a radiative‐convective instability which is relevant to Earth's tropics. The super‐greenhouse is caused by the low troposphere becoming optically thick, causing a positive feedback on near surface temperature and moisture, driving deep convection, column moistening, and reduced outgoing longwave radiation. Aspects of the runaway greenhouse physics are implicated, but a local runaway greenhouse is avoided. These results have implications for understanding the response of the tropics to a warming world.