Climate change mitigation is a global collective action problem, yet the shift from the Kyoto Protocol’s binding targets to the Paris Agreement’s voluntary nationally determined contributions has fundamentally changed how international cooperation works. My research in this area examines public support for unilateral versus reciprocal climate policy — whether citizens are willing to support domestic action even when other countries fail to do their part. Using survey experiments in countries including China and the United States, this work shows that public support for climate action is surprisingly resilient to information about other countries' non-compliance, with important implications for the political sustainability of the Paris approach.