Target carbon's costs, policy designs, and developing countries

Common views hold that the efficient way to limit warming to a chosen level is to price carbon emissions at a rate that increases exponentially. We show that this Hotelling tax on carbon emissions is actually inefficient. The least-cost policy path takes advantage of the climate system's inertia to delay reducing emissions and allow greater cumulative emissions. The efficient carbon tax follows an inverse-U-shaped path and grows more slowly than the Hotelling tax. Economic models that assume exponentially increasing carbon taxes are overestimating the cost of limiting warming, overestimating the efficient near-term carbon tax, and overvaluing technologies that mature sooner. (JEL H23, Q54, Q58)

Leaded gasoline is still used globally for aviation and automotive racing. Exploiting regulatory exemptions and a novel quasi-experiment, we find that leaded gasoline use in racing increases ambient lead, elevated blood lead rates, and elderly mortality. The mortality estimates indicate that each gram of lead added to gasoline exceeds $1,100 in damages. Our setting allows us to rule out potential confounders, such as correlated pollutants or socioeconomic status. We provide the first causal estimates linking adult mortality to leaded gasoline, highlight the value of banning on-road leaded gasoline, and present policy-relevant cost estimates at the lowest ambient levels to date. (JEL I12, J14, L71, Q51, Q53)

Uncertainty is critical to questions about climate change policy. Recently developed recursive integrated assessment models have become the primary tools for studying and quantifying the policy implications of uncertainty. We decompose the channels through which uncertainty affects policy and quantify them in a recursive extension of a benchmark integrated assessment model. The first wave of recursive models has made valuable, pioneering efforts at analyzing disparate sources of uncertainty. We argue that frontier numerical methods will enable the next generation of recursive models to better capture the information structure of climate change and to thereby ask new types of questions about climate change policy.

Ozone levels in U.S. national parks are similar to those of U.S. cities, and are negatively associated with visitation.