Adjusted Net Savings needs adjusting: reassessing human and resource factors in sustainability

We extend Stiglitz’s 1974 theoretical model of closed-economy growth with a non-renewable resource, by adding resource discovery; human capital, some of it created outside GDP; knowledge capital, which generates positive spillovers; and depreciation of all capitals. We assume exponential growth always, not just asymptotically, and thus derive consistent sectoral shares of expenditure and wealth. We give three calibrations of this model using data for 1995-2014, when global economic aggregates grew approximately exponentially, and calculate the Adjusted Net Savings (ANS) sustainability indicator in each. In all three, “human factors” in ANS – spending on education and R&D, the value of total factor productivity (TFP) growth, and stocks dilution by population growth – and the resource component differ markedly from the World Bank’s ANS estimates; so its ANS methodology ideally needs adjusting, in order to better inform countries’ policymaking. Inspired by earlier estimates, our third calibration assumes three times the World Bank’s estimated expenditures on human and knowledge capital investment, and that half human capital investment is in measured GDP. This eliminates any TFP growth needed to explain observed 1995-2014 growth, and reconciles conflicting estimates of the resource’s output power, while population dilution and resource discovery remain as significant ANS components.