Growth and Mitigation Policies with Uncertain Climate Damage

We analyze an endogenously growing economy in which production generates greenhouse gas emissions leading to global temperature increase. Global warming causes stochastic climate shocks, modeled by the Poisson process, which destroy part of the economy's capital stock. Part of the output may be devoted to emissions abatement and thus damages from climate shocks may be reduced. We solve the model in closed form and show that the optimal path is characterized by a constant growth rate of consumption and capital stock until a shock arrives, triggering a downward jump in both variables. The magnitude of the jump depends on the Poisson arrival rate, abatement efficiency, damage intensity, and the elasticity of intertemporal consumption substitution. Optimum mitigation policy consists of spending a constant share of output on abatement, which is an increasing function of the Poisson arrival rate, the economy's productivity, polluting intensity of output, and the intensity of environmental damage. Optimum growth and abatement react sharply to changes in the arrival rate and the damage intensity, suggesting more stringent climate policies for a realistic world with uncertainty compared to the certainty-equivalent case. We extend the baseline model by adding climate-induced fluctuations around the growth trend and stock pollution effects, showing the robustness of our results.