More is Less: the Tax Effects of Ignoring Flow Externalities

Using a model of nonlinear decay of the stock pollutant, and starting from the same initial conditions, the paper shows that an optimal tax that corrects for both stock and ßow externalities may result in a lower tax, fewer cumulative emissions (less decay) and higher output at the steady state than a corrective tax that ignores the ßow externality. The “more is less” result emphasizes that setting a corrective tax that ignores the ßow externality, or imposing a corrective tax at too low a level where there exists only a stock externality, may affect both transitory and steady state output, tax payments and cumulative emissions. The result has important policy implications for decision makers setting optimal corrective taxes and targeted emission limits whenever stock externalities exist. JEL Classification: H21, Q25