Navigating green Seas: An open-source tool for costing the development of green shipping corridors

• Open-source model for assessing green shipping corridors with low-carbon fuels. • Route-specific costs and emissions analysed for ammonia, methanol, and blends. • Methanol achieves $240–350/tCO 2 -eq – lowest abatement cost across all fuels. • Ammonia cuts 87–88% CO 2 -eq at $340–590/tCO 2 -eq with SCR and exhaust controls. • Shift to Methanol enables the lowest fuel-switch cost and emissions trade-off. The adoption of low-carbon ammonia and low-carbon methanol is widely regarded as a key, viable strategy for decarbonising the global maritime sector. While there exists analysis on the relative economic and environmental impacts of using alternative fuels, there is limited literature that integrates both environmental impact and economic analysis of the development of individual green shipping corridors. Moreover, as this industry transitions to the use of low-carbon fuels, the use of fuel additives to enable the blending of methanol and maritime fuels up to 20% (v/v) could potentially offer a low-cost, near-term option for reducing shipping emissions with minimal impact to current infrastructure. Herein, we present an open-source model that encompasses fuel storage, ship capital, and operating costs, developed to assist stakeholders in assessing the costs of shipping with ammonia, methanol, and methanol fuel blends for individual shipping trade routes. The model is applied to major global trade routes for container, bulk carrier and chemical tanker routes, accounting for 29% of total global shipping volume. Our analysis indicates that switching to ammonia or methanol fuel incurs carbon abatement costs of 590 US$/tonne CO2-eq and 350 US$/tonne CO2-eq , respectively, for a 100-year global warming potential. Our results show that decarbonisation costs scale with both trade volume and voyage distance, with high-volume bulk corridors offering the lowest marginal abatement costs per tonne-kilometre, while long-haul container trades face the highest cost premiums.