Carbon markets
Mitigation Contribution (Article 6.4)
Definition
A mitigation contribution A6.4ER (or mitigation contribution unit, MCU) is a credit issued under the Paris Agreement Crediting Mechanism (Article 6.4) that the host country does not authorise for international transfer: the underlying emission reduction or removal counts toward the host Party's own NDC, and no corresponding adjustment is required. Authorised A6.4ERs, by contrast, become internationally transferred mitigation outcomes (ITMOs) with corresponding adjustments.
References
Supports definition and framing.
Overview
What it means
The distinction determines who may claim the reduction. MCUs can be purchased by domestic or voluntary buyers to finance host-country mitigation without double counting, and can potentially be authorised later if not yet transferred.
How it is used
Under rules finalised around COP29, project developers register activities with the Article 6. 4 Supervisory Body; buyers seeking voluntary claims without offsetting the host's target use MCUs, while compliance buyers seek authorised, correspondingly adjusted credits.
Why it matters
The authorised/unauthorised split is the core integrity mechanism of Article 6. 4 — it determines whether carbon finance adds to global ambition or merely relocates credit for the same tonne.