All adrift: aviation, shipping, and climate change policy

All sectors face decarbonization for a 2 °C temperature increase to be avoided. Nevertheless, meaningful policy measures that address rising CO 2 from international aviation and shipping remain woefully inadequate. Treated with a similar approach within the United Nations Framework Convention on Climate Change (UNFCCC), they are often debated as if facing comparable challenges, and even influence each others' mitigation policies. Yet their strengths and weaknesses have important distinctions. This article sheds light on these differences so that they can be built upon to improve the quality of debate and ensuing policy development. The article quantifies '2 °C' pathways for these sectors, highlighting the need for mitigation measures to be urgently accelerated. It reviews recent developments, drawing attention to one example where a change in aviation mitigation policy had a direct impact on measures to cut CO 2 from shipping. Finally, the article contrasts opportunities and barriers towards mitigation. The article concludes that there is a portfolio of opportunities for short- to medium-term decarbonization for shipping, but its complexity is its greatest barrier to change. In contrast, the more simply structured aviation sector is pinning too much hope on emissions trading to deliver CO 2 cuts in line with 2 °C. Instead, the solution remains controversial and unpopular - avoiding 2 °C requires demand management. Policy relevance The governance arrangements around the CO 2 produced by international aviation and shipping are different from other sectors because their emissions are released in international airspace and waters. Instead, through the Kyoto Protocol, the International Civil Aviation Authority (ICAO) and the International Maritime Organization (IMO) were charged with developing policies towards mitigating their emissions. Slow progress to date, coupled with strong connections with rapidly growing economies, has led to the CO 2 from international transport growing at a higher rate than the average rate from all other sectors. This article considers this rapid growth, and the potential for future CO 2 growth in the context of avoiding a 2 °C temperature rise above pre-industrial levels. It explores similarities and differences between these two sectors, highlighting that a reliance on global market-based measures to deliver required CO 2 cuts will likely leave both at odds with the overarching climate goal.