Abstract
The problem of calculating the global entropy production of the climate system is revisited. In the first place, means to set forth the entropy production due to absorption and emission of electromagnetic radiation are recalled. Some recent formulae to estimate the global entropy production are exposed as ill-founded, in spite of correct earlier treatments based on Planck's classic theory. A conceptual model of climate is used to ease the discussion of some pertinent rates that have been proposed. Formal simplicity may be achieved by the introduction of radiation temperatures put forward in recent years, so as to express the density of the entropy production rates in energy exchanges between matter and radiation as simple bilinear forms. It is argued that the Clausius-Duhem inequality of continuum mechanics, widely applied in meteorology, insufficiently represents the planetary thermodynamics when radiation fields play a role. It is the entropy inequality of modern continuum thermodynamics that truly reflects the second law of thermodynamics.
