We investigate the impact of three norms on the willingness of respondents (n=7,231) from India, S. Africa, China, the U.S., and the E.U. to contribute towards climate change mitigation in a threshold global public good game setting. We find robust evidence of a reciprocity norm as well as a social efficiency norm in all five samples, while the fairness norm was only detected in the S. African and the U.S. samples. We also find substantial heterogeneity in norm sensitivity between countries.