[Wonder Warthog]

"That concept made it into the computer game "Sim City", but obviously one wonders what kind of long term heating of the atmosphere would result."

None (directly). The wavelength chosen for transmission will be one to which the atmosphere is transparent. Now, indirectly, ALL of the energy will ultimately show up as heat in the atmosphere. Thermodynamics, y'know.

[SunkenCiv]

IOW, no extra heating -- since the light converted in orbit would have been intercepted by the Earth anyway -- and actually cooling -- because the best available photovoltaics are only 30 per cent efficient.