Uncertain Outcomes and Climate Change Policy

Focusing on tail effects, I incorporate distributions for temperature change and its economic impact in an analysis of climate change policy. I estimate the fraction of consumption w(τ ) that society would be willing to sacrifice to ensure that any increase in temperature at a future point is limited to τ . Using information on the distributions for temperature change and economic impact from studies assembled by the IPCC and from “integrated assessment models” (IAMs), I fit displaced gamma distributions for these variables. Unlike existing IAMs, I model economic impact as a relationship between temperature change and the growth rate of GDP as opposed to its level, so that warming has a permanent impact on future GDP. The fitted distributions for temperature change and economic impact generally yield values of w(τ ) below 2%, even for small values of τ , unless one assumes extreme parameter values and/or substantial shifts in the temperature distribution. These results are consistent with moderate abatement policies. JEL Classification Numbers: Q5; Q54, D81