ON THE CONCEPT OF GREEN NATIONAL INCOME

The present paper generalizes the Weitzman/Hartwick approachto national income accounting. We first establish a close generalrelation between the current value Hamiltonian of an optimalcontrol problem and the optimal value of the objective integralif the time argument does not enter the constraints and entersthe objective function only as a discount factor. This resultis applied to a simple economic model covering most models foundin the literature on national income accounting involving pollutionand non-renewable resources. We critically review the usefulnessof net national product as a welfare indicator and as an indicatorfor sustainability.