That's actually a really good question. It does make me question the hypothesis, which is essentially, is the entropy any different to a lifeless planet just re-radiating solar energy. The answer is probably, not in the long term. You may be able to use the principle to determine what stage intelligent life is in though? If we were talking plants only, the re-emitted radiation would be expected to be reduced, as it is bound up in the growth. But our species is now expending that, so at this moment, solar re-radiation we would expect to be above lifeless levels.