This paper establishes a statistically and economically significant cross-country relationship between national responses to climate change and genetic distance, which is a proxy for countries’ dissimilarities in cultures, ancestry, and historical legacies associated with long-term exposure to divergent historical trajectories. It finds that countries that are genetically distant to the world-leading nation-state of climate change mitigation tend to experience barriers to the cross-border diffusion of climate change policies and hence exhibit worse responses to climate change. A potential explanation is that climate change polices are more likely to spread between closely related countries with more similar preferences for the provision of the public goods of environmental and climate protection. The findings imply that strengthening climate change mitigation requires overcoming obstacles to international policy diffusion.