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3. A. H. Oort and J. P. Peixoto: Physics of Climate, American Institute of Physics, New York, 1992.
4. F. D’Isep and L. Sertorio: Maximum mechanical work from the steady energy circulation on a finite body, Il Nuovo Cimento 67, 1982.
5. We thank Professor Longhetto, University of Torino, for having provided these data.