International Climate Agreements under The Threat of Solar Geoengineering

The possibility of overshooting global emissions targets has triggered a public debate about the role solar geoengineering (SGE) - using technologies to reflect solar radiation away from Earth - may play in managing climate change. One major concern is that SGE technologies are relatively cheap, and could potentially be deployed by a single nation (the “free driver”) that could effectively control the global climate. Another concern is that SGE opportunities may alter countries’ incentives to cooperate on abatement. Here we develop a game-theoretic model to analyze how opportunities to deploy SGE impact global abatement and the effectiveness of international environmental agreements (IEAs) on climate change. We show that non-cooperative abatement levels may increase or decrease under the threat of SGE, depending on how damaging the free-driver’s level of deployment is on others. We also show the stability of IEAs that govern abatement is challenged by two competing strategic incentives. One is a familiar free-rider incentive, which is the benefit a country earns by leaving an agreement and lowering its abatement. The other incentive is the benefit a country earns by joining an agreement and increasing abatement in order to motivate the free-driver to reduce its level of deployment. We introduce the term anti-driver to describe this second incentive. Ultimately, we find that if the anti-driver incentives are high enough, the threat of SGE can expand both the depth (i.e., abatement level) and breadth (i.e., participation level) of stable IEAs compared to a world without SGE.