  Convective and radiative cooling are the two principle mechanisms by which
the Earth's surface transfers heat into the atmosphere and that shape surface
temperature. However, this partitioning is not sufficiently constrained by
energy and mass balances alone. We use a simple energy balance model in which
convective fluxes and surface temperatures are determined with the additional
thermodynamic limit of maximum convective power. We then show that the broad
geographic variation of heat fluxes and surface temperatures in the
climatological mean compare very well with the ERA-Interim reanalysis over land
and ocean. We also show that the estimates depend considerably on the
formulation of longwave radiative transfer and that a spatially uniform offset
is related to the assumed cold temperature sink at which the heat engine
operates.
