Carbon markets are considered a key policy tool to achieve cost-effective climate mitigation1, 2. Project-based carbon market mechanisms allow private sector entities to earn tradable emissions reduction credits from mitigation projects. The environmental integrity of project-based mechanisms has been subject to controversial debate and extensive research1, 3, 4, 5, 6, 7, 8, 9, in particular for projects abating industrial waste gases with a high global warming potential (GWP).