Voluntary participation can improve multilateral environmental governance. We model voluntary participation of states in unanimously approved federal environmental policy. A Pareto-improving federal emission price coexists with state-level emission pricing. Federal revenues are distributed equally per capita (egalitarian), in proportion to states' historical emission levels (sovereignty), or states’ actual payments (juste retour). We find that the existence of Pareto-improving uniform federal prices depends on wealth differences, transfer rules, and on whether or not states anticipate transfers. Sovereignty transfers work in all cases. Differences in wealth can undermine egalitarian transfers. Juste retour transfers render federal policy ineffective if states anticipate them. The richest state prefers the lowest Pareto-optimal federal price (“minimum price”) as it becomes the largest net-donor. Adding different population sizes, the richest and largest (smallest) state prefers the minimum price with sovereignty and juste retour transfers (egalitarian transfers). Therefore, rich states brake and simultaneously make possible passing unanimous federal policy.

自愿参与可以改善多边环境治理。我们模拟各州自愿参与一致批准的联邦环境政策。帕累托改进的联邦排放价格与州级排放定价共存。联邦收入按人均（平等主义）平均分配，与各州的历史排放水平（主权）或各州的实际支付（juste retour）成比例。我们发现帕累托改善统一联邦价格的存在取决于财富差异、转移规则以及各州是否预期转移。主权转让适用于所有情况。财富差异会破坏平等转移。如果各州预期，Juste retour transfer 会使联邦政策失效。最富有的州更喜欢最低的帕累托最优联邦价格（“最低价格”），因为它成为最大的净捐助者。加上不同的人口规模，最富有和最大（最小）的国家更喜欢具有主权和正义回归转移（平等转移）的最低价格。因此，富裕的州会阻止并同时使通过一致的联邦政策成为可能。