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We study the international diffusion of carbon pricing policies and quantify its global benefits. We first empirically examine to what extent the adoption of carbon pricing in one country can explain the subsequent adoption of carbon pricing in other countries. We find robust and statistically significant evidence for policy diffusion. For two neighbouring countries, policy adoption in one country increases the probability of subsequent adoption in the other country on average by several percentage points. We then use Monte Carlo simulations to translate our empirical estimates into global emission reductions from diffusion. The results suggest that for many countries, emission reductions from policy diffusion can be larger than domestic emission reductions. Overall, our results provide additional support for the adoption of stringent climate policies, especially in countries where climate change mitigation might have been considered as being of relatively little importance because of relatively small domestic emissions.Despite the need for more stringent climate policies to achieve the Paris climate targets (IPCC 2021), many countries appear reluctant to ratchet up their mitigation efforts. This may partly be because the costs of mitigation are incurred domestically and immediately while most of its benefits will be reaped globally and in the future, but more ambitious climate action is also hindered by possible concerns about the limited effectiveness of domestic abatement efforts if other countries do not similarly reduce their greenhouse gas (GHG) emissions. This consideration is especially pertinent in relatively small countries. Indeed, in 2021 the smallest 90% of emitters contributed only about 20% of global GHG emissions. This narrow perspective neglects, however, that international leadership in climate change mitigation can yield substantial benefits beyond domestic emission reductions 1, 2 . For example, stringent climate policies at home can support international diffusion of technological innovations that reduce mitigation costs in other countries 3,4 . Furthermore, domestic climate policies can demonstrate political feasibility and certain benefits of carbon pricing 5 , and they can create incentives related to trade 6 and diplomacy 7 that can nudge other countries to adopt the same or similar policies. This latter process whereby adoption of a policy in one country increases the probability of adoption in other countries is usually referred to as policy diffusion 8 .Results from qualitative studies provide ample evidence for climate policy diffusion. For example, evidence has been described for strong mutual influences among the world's first adopters of carbon pricing policies in Scandinavia in the 1980s 9 . According to 10 , the subsequent adoption of carbon pricing by other countries can at least partially be explained with emulation of earlier policies and learning from prior experiences. International diffusion has also been actively promoted by early adopters themselves and through multilater...