It is commonly assumed that a coordinated international legal response would be the best way to mitigate climate change. Finding an effective solution for all key countries and sectors is, however, proving to be a considerable challenge. This article focuses on attempts to address sectoral emissions from international aviation and maritime transport outside the United Nations Framework Convention on Climate Change (UNFCCC). It highlights that emissions from these two sectors are growing significantly and have been discussed under the auspices of the International Civil Aviation Organization and International Maritime Organization for nearly two decades without an effective multilateral solution. The article argues that the lack of global agreement on how to address emissions from these two sectors has increased the temptation for independent action. Most notably, the European Union has already included emissions from all flights to and from European airports, including those by foreign airlines, into its emissions trading scheme and is in the process of considering measures to address emissions from international maritime transport. This has sparked both a heated political row and legal debate on the permissibility of unilateral trade measures to mitigate climate change. Against this background, the article analyzes whether and how independent action can promote mitigation action in these sectors, and whether it should be seen as unhelpful climate unilateralism or useful ‘minilateralism’ and migration of legal norms that serve to advance the ultimate objective of avoiding dangerous anthropogenic climate change.