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Maritime transport accounts for around 3% of global anthropogenic greenhouse gas (GHG) emissions (Well-to-Wake). These GHG emissions must be reduced by at least 50% in absolute values by 2050 to contribute to the ambitions of the Paris Agreement signed in 2015. Switching to zero-carbon fuels made from renewable sources (hydro, wind, or solar) is seen by many as the most promising option to deliver the desired GHG reductions. However, renewable energy is a scarce resource that gives a much larger GHG reduction spent within other sectors. This study explores how to reach the IMO 2050 GHG targets exclusively through energy efficiency measures. The results indicate that by combining wind-assisted ship propulsion (WASP) with a slender hull form, fuel consumption and GHG emissions can be reduced by 30–35%, at a negative abatement cost for speeds exceeding 8 knots. Where the cost saving increases with the speed because at higher speeds, the fuel accounts for a higher share of the total cost, which implies that the cost saving goes from zero at 8 knots, to 5% reduction at 11 knots average speed to 14% reduction of total cost with 15 knots average speed. In comparison, GHG reductions through zero-carbon fuels will increase transport costs by 50–200%.

Introduction

From the first days of our civilization, sea transport has enabled regional and global trades. Today, sea transport accounts for 80% of the global trade measured in ton-miles (UNCTAD 2021) and 3% of greenhouse gas (GHG) emissions measured Well-to-Wake (Lindstad et al. 2021). More than 40% of this sea trade is performed by dry bulkers, making them the real workhorses of the sea. Even though sea transport is energy efficient compared to other transport modes, all sectors need to reduce their GHG emissions by at least 50% in absolute values by 2050 to contribute to the Paris Agreement (UNFCCC 2015). According to Bouman et al. (2017), the desired energy and GHG reductions can be achieved through: Design and other technical improvements of ships; Operational improvements; Fuels with zero or low GHG footprints; or a combination of these.

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