This report draws on analysis of international law to explore the legal implications of action by one State or multiple States to reduce GHGs in the maritime sector outside of the International Maritime Organisation.

It finds that provided a few important legal and enforcement considerations are respected and built into the design of any policy measure, there are no legal obstacles to national or regional action, indeed, countries are obligated to take such action. If the IMO enacts regulations in line with the Paris Agreement countries could then be relieved of that obligation but countries cannot simply wait for ambitious IMO regulation to appear. The primary obligation for Paris Agreement signatories is to reduce shipping emissions nationally or regionally.