A new metric for assessing planetary surface habitability

Planetary surface habitability has so far been, in the main, considered in its entirety. The increasing popularity of 3-D modelling studies of planetary climate has highlighted the need for a new measure of surface habitability. Combining known thermal limits of Earth-based life with surface water fluxes, we introduce such a measure which can be calculated from the climatological output from general circulation model simulations. In particular, we pay attention to not only 'complex' life, but additionally the temperature limits of microbial and extremophilic life which have been vital to the generation of Earth's own biosignatures. This new metric is validated on Earth using ERA5 reanalysis data along with multiple datasets representing Earth-based life, as well as compared to the patterns of habitability of a model ensemble simulating an aquaplanet-Earth.