Imposing sanctions on noncompliant parties to international agreements is often advocated as a remedy for international cooperation failure, notably in climate agreements. We provide an experimental test of this conjecture in a collective-risk social dilemma simulating the effort to avoid catastrophic climate change. We involve groups of participants from two cultural areas that were shown to achieve different levels of cooperation nationally when peer-level sanctions were available. Here we

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... w that, while this result still holds nationally, international interaction backed by sanctions is overall beneficial. Cooperation by low cooperator groups increases significantly in comparison with national cooperation and converges to the cooperation levels of high cooperation groups. While the increase is only marginally significant without sanctions, it becomes sizable when sanctions are imposed. When sanctions are available, individuals are willing to cooperate above the level that would maximize expected payoffs. Revealing or hiding counterparts' nationality does not affect results.