Escaping Damocles' Sword: Endogenous Climate Shocks in a Growing Economy

We consider a growing economy which is subject to recurring, random, uninsurable, and potentially large and long-lasting climate shocks leading to destruction of infrastructure, land degradation, collapse of ecosystems or similar loss of productive capacity. The associated damages and the hazard rate are endogenously driven by the stock of greenhouse gases. We highlight the important role of the relative risk aversion and provide analytical solutions for the optimal climate policy, the growth rate and the saving propensity of the economy. We stress the importance of jointly determining these variables, especially if the objective is to formulate meaningful policy prescriptions. If, for example, the growth rate or the saving rate are assumed to be exogenous, and thus independent of the characteristics of climate shocks and economic fundamentals, then future economic developments in the face of climate change and, consequently, the future mitigation efforts will deviate from the optimal paths. In a quantitative assessment we show that with log-utility and under favorable technological and climatic conditions the abatement expenditure represents only 0.5% of output, equivalent to $37 per ton carbon. Under less favorable conditions, coupled with a relative risk aversion which exceeds unity, the abatement propensity increases to 2.9%, equivalent to $212 per ton carbon, and it jumps to a striking 16% in the pessimistic scenario involving severe shocks and low efficiency of abatement technology.