International emissions trading
There can be civil or criminal penalties applied for non-compliance.

See for example:
https://www.gov.uk/government/publications/environment-agency-enforcement-and-sanctions-policy/annex-2-climate-change-schemes-the-environment-agencys-approach-to-applying-civil-penalties

https://www.daera-ni.gov.uk/articles/euets-fees-charges-and-civil-penalties

International trading schemes depend on international law. Membership of such schemes will depend on accepting an adjudication body to rule on breaches, as with any other international contractual agreement.