Systematic review of the actual emissions reductions of carbon offset projects across all major sectors

Abstract

Net-zero targets have significantly increased carbon offset demand. Carbon offsets are issued based on ex-ante estimates of project emissions reductions, though systematic evidence on ex-post evaluations of achieved emissions reductions is missing. We synthesized existing rigorous empirical studies evaluating more than 2,000 offset projects across all major offset sectors. Our analysis shows that offset projects achieved considerably lower emissions reductions than officially claimed. We estimate that only 12% of the total volume of existing credits constitute real emissions reductions, with 0% for renewable energy, 0.4% for cookstoves, 25.0% for forestry and 27.5% for chemical processes. Our results thus indicate that 88% of the total credit volume across these four sectors in the voluntary carbon market does not constitute real emissions reductions. This offset achievement gap corresponds to almost twice the annual German CO2 emissions. We complement evidence from offset projects with 51 additional studies conducting ex-post evaluations of field interventions with settings comparable to offset projects. For cookstoves and forestry projects, these field interventions were more effective at reducing emissions than the voluntary offset projects, likely due to more careful intervention targeting, stricter monitoring and enforcement of intervention protocols.