Analysis of the Effect of Vessel Speed Reduction Policies on Carbon Dioxide Emissions in Nigerian Coastal Shipping

Speed reduction, often referred to as slow steaming, has emerged as one of the most immediately effective technical and operational measures for reducing maritime carbon dioxide emissions and is now referenced within the IMO's Carbon Intensity Indicator regulatory framework. This study analyses the potential effect of mandatory or incentivised speed reduction policies on carbon dioxide emissions from vessels engaged in Nigerian coastal trade. Drawing on a quantitative emissions modelling methodology, the study constructs a route-by-route emissions inventory for forty-five vessels operating on the principal coastal routes between Lagos, Warri, Port Harcourt, and Calabar, using noon report fuel consumption data for the years 2021 to 2023. The MEPC emissions factor methodology is applied to convert fuel consumption to carbon dioxide equivalent. Alternative speed scenarios representing ten, fifteen, and twenty percent reductions from average voyage speed are modelled, and their emissions impacts are calculated against the baseline inventory. Results indicate that a uniform fifteen percent speed reduction across the coastal fleet would achieve a carbon dioxide emissions reduction of between twenty-two and twenty-eight percent compared to the three-year baseline, with corresponding reductions in fuel expenditure that would be economically beneficial for operators at current bunker prices. The study contributes a quantified emissions model for the Nigerian coastal sector, which is absent from existing maritime decarbonisation literature. Keywords: slow steaming, carbon dioxide emissions, coastal shipping, emissions modelling, IMO Carbon Intensity Indicator