Planck feedback ($\partial (\sigma T^4)/\partial T=4\sigma T^3$)

The Planck feedback is the stabilizing increase in outgoing thermal radiation when temperatures rise, with other properties held fixed. For a blackbody the local derivative is $4\sigma T^3$, so a colder emitter has a smaller absolute radiation increase per kelvin. The atmospheric response requires radiative transfer, and cannot be obtained by replacing the entire climate system with a single surface blackbody.