When considering public support for domestic policies that contribute to a global public good, such as climate change mitigation, the behavior of other countries is commonly regarded as pivotal. Using survey experiments in China and the United States we find that other countries’ behavior matters for public opinion, but in a contingent manner. When citizens learn that other countries decrease their emissions, this leads to support for further domestic action. Yet, support for reciprocal behavior is not a necessary consequence of other countries increasing their emissions. Responding in-kind to emissions increases abroad depends upon the home country’s past behavior and who the other country is. Our results imply that the international context remains important, despite global climate policy now relying more on coordinated unilateral action and polycentric governance. They also show, however, that we need to pay greater attention to contingent effects of countries’ positive and negative behavior in this area.