Expert Assessments of Maritime Shipping Decarbonization Pathways by 2030 and 2050

Abstract International shipping conveys over 80% of global trade by volume and emits an estimated 3% of the world's greenhouse gases (GHGs). There are many potential pathways and barriers to decarbonizing the diverse and fragmented international shipping sector, with numerous uncertainties. Here, we employ expert elicitation, gathering perspectives from 149 world‐leading experts in maritime shipping and decarbonization, to characterize uncertainties in shipping decarbonization pathways. These experts predict a 30%–40% (25th–75th percentile range) carbon intensity reduction by 2030 compared to 2008, meeting the International Maritime Organization's (IMO) target. By 2050, they anticipate an approximate 40%–75% cut in GHG emissions, falling short of the IMO's 2050 net‐zero GHG goal. Responding experts see decarbonization occurring through three types of measures: operational, technological, and alternative energy sources. In the short‐term, decarbonization is predicted to be dominated by operational measures, while in the long‐term, it will be dominated by alternative energy, although there is no consensus on which fuels will dominate. Technological upgrades are expected to play crucial supporting roles. The experts believe that differences in business models and governance may lead to different decarbonization pathways by ship segment. The experts' qualitative responses highlight: alternative energy systems, ship fleet turnover, spillover effects from other sectors, reducing industry pessimism, and the supply chain as critical leverage points that can propel shipping toward sustainable decarbonization pathways. Navigating this transition demands support from key levers identified in this study: politics and policy, maritime governance, and contractual architecture.