The sum of surface accumulation and surface ablation. This is the sense in which the term is understood in descriptions of measurements by the glaciological method, in which the internal mass balance is treated separately. Recently, in estimates of ice-sheet mass balance by modelling, the term has been extended to include internal accumulation. This extended meaning is discouraged. The unambiguous term climatic mass balance is recommended for the sum of the surface mass balance and the internal mass balance.