We investigate whether trade sanctions against outsiders can foster climate cooperation in self-enforcing international environmental agreements if outsiders retaliate. We find a threshold effect: In small coalitions incentives to be a coalition member decrease whereas in large coalitions they increase. Thus, trade sanctions can be an effective tool in climate policy only after a sufficiently large climate coalition has already been formed. Even if larger stable coalitions are achieved with trade sanctions, implications for global welfare can be adverse, because additional trade distortions trade off with the environmental gains. We identify the USA and Europe as essential members of stable coalitions if outsiders retaliate.

我们调查了针对外来者的贸易制裁是否可以在外来者报复的情况下促进气候合作，以自我执行国际环境协议。我们发现了一个阈值效应：在小联盟中，成为联盟成员的动机减少，而在大联盟中，它们增加。因此，只有在足够大的气候联盟已经形成之后，贸易制裁才能成为气候政策的有效工具。即使通过贸易制裁实现了更大的稳定联盟，对全球福利的影响也可能是不利的，因为额外的贸易扭曲会与环境收益进行权衡。如果外人进行报复，我们将美国和欧洲视为稳定联盟的重要成员。