International Shipping in a World below 2 °C

The decarbonization 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-1. Here we perform a multi-IAM analysis of international shipping and show the potential for decreasing annual emissions in the next decades, with reductions of 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 decarbonization of international shipping, with drop-in biofuels, renewable alcohols and green ammonia standing out as the main substitutes for conventional maritime fuels. While our results align with the 2018 emission reduction goal of the International Maritime Organization, their compatibility with the agency's revised target is still subject to a more definitive interpretation. International maritime shipping accounts for an important proportion of global CO2 emissions, but its role in a world with deep decarbonization has not been thoroughly examined. Through a multi-model comparison, this study reveals the necessity of reducing and stabilizing emissions from this sector in the next few decades.