1. Same as thermodynamic efficiency. 2. In climatology, an expression of the effectiveness of temperature in determining the rate of growth, assuming sufficient moisture. The idea was introduced by B. E. And G. J. Livingston (1913). It was applied by C. W. Thornthwaite (1948) in his system of climatic classification. The recognition of this general concept led to one of the first uses of the degree-day, that is, application to plant growth and relationship to the phenological effective temperature of about 42°F. Compare precipitation effectiveness.