International Climate Agreements under the Threat of Solar Geoengineering

The possibility of overshooting global emissions targets has triggered a debate about the role of solar geoengineering (SGE)-using technologies to reflect solar radiation away from Earth-in managing climate change. One major concern is that SGE technologies are relatively cheap and could potentially be deployed by a single country (the "free driver"). We develop a model to analyze how opportunities to deploy SGE impact global abatement and the effectiveness of international environmental agreements (IEAs). We show that noncooperative abatement may increase or decrease under the threat of SGE, depending on how damaging the free driver's level of deployment is to others. When free-driver externalities are significant, other countries have additional incentives to abate-called anti-driver incentives-to reduce the free driver's deployment. We also show that compared to a world without SGE opportunities, stable IEAs can be large (small) if anti-driver incentives are relatively strong (weak).