Marine fuel choices and related life cycle environmental impacts under global shipping policies.

Policies can drive the energy transition in the shipping sector, which accounts for 3% of global greenhouse gas emissions. Various shipping policies are explored using a sector-coupled global energy system model with a detailed shipping module and considering environmental impacts from a life cycle perspective. While the proposed 'IMO net-zero framework' drives biofuel use, it may not be adequate for the broader adoption of low-carbon fuels required to achieve net-zero emissions targets. A combined levy and global fuel standards mechanism could accelerate the uptake of low-carbon fuels, as compared to the proposed IMO policy. In most policies, ammonia is a cost-effective fuel for ships, whereas electrification is preferred for vessels with the possibility to bunker daily. Ammonia derived from bioenergy with carbon capture, yielding negative emissions, and e-ammonia, are crucial to reach global climate targets. This energy transition risks having other environmental impacts, including land use and mineral resource depletion.