International shipping in a world below 2°C

The decarbonisation of shipping has become an important policy goal. While Integrated Assessment Models (IAMs) are often used to explore climate mitigation strategies, they typically provide little information on international shipping, which accounts for emissions of around 0.7 GtCO2/yr. We perform the first multi-IAM analysis of international shipping, drawing on the results of six global models. Results indicate the need for decreasing annual emissions in the next decades, with reductions up to 86% by 2050. This is primarily achieved through the deployment of low-carbon fuels. Models that represent several potential low-carbon alternatives tend to show a deeper decarbonisation of international shipping, with drop-in biofuels, renewable alcohols and green ammonia standing out as the main substitutes of conventional maritime fuels. While our results align with the 2018 emissions reduction goal of the International Maritime Organization, their compatibility with the agency’s revised target is still subject to a more definitive interpretation.