The Clean Development Mechanism (CDM) has allowed industrialized countries to buy credits from developing countries for the purpose of meeting targets under the Kyoto Protocol. In principle, the CDM simply shifts the location of emission reductions, with no net mitigation impact. Departing from this zero-sum calculus, the Cancun Agreements reached at the sixteenth session of the Conference of the Parties (COP) in 2010 called for "one or more market-based mechanisms" capable of "ensuring a net decrease and/or avoidance of global greenhouse gas emissions", an intention reiterated at COP 17 and COP 18. This article explores the extent to which the CDM may or may not already lead to such a "net decrease." It finds that the CDM's net mitigation impact likely hinges on the additionality of large-scale power projects, which are expected to generate the majority of CDM credits going forward. If these projects are truly additional and continue to operate well beyond the credit issuance period, they will decrease global greenhouse gas emissions. However, if they are mostly non-additional, as research suggests, they could increase global greenhouse gas emissions. The article closes with a discussion of possible means to increase mitigation benefit. (C) 2014 Elsevier Ltd. All rights reserved.