Difficult to Decarbonise? Options for Reducing Emissions from International Shipping

International shipping is responsible for 3% of global greenhouse gas emissions [6], roughly equivalent to the emissions produced by Germany [7]. Under a business-as-usual-scenario, these emissions are expected to increase between 50% and 250% by 2050 [1]. Failure to reduce maritime pollution would worsen our air quality and raise instances of acid rain [5], contributing to the acceleration of climate change. Even though deep-sea shipping was branded a “difficult to decarbonise” industry, the Paris Climate Agreement set this sector a target of zero emissions by 2050 [6]. The following will explore some pathways the shipping industry could take to strive toward decarbonisation.

Alternative fuels

At first glance, there is a range of alternative fuels for international shipping. But finding a fuel that can be produced sustainably and at a large enough scale to meet the global demand is far and few between [2]. Some replacement fuels, such as liquified natural gas, can actually have a worse impact on climate change than the fuel it replaces [2]. While this carbon-based liquid [6] has become a popular fossil-fuel replacement for shipowners [2], if not contained adequately, unburnt methane can escape into the atmosphere [6]. Sustainability maritime experts have therefore urged for investment elsewhere. In particular, importance is placed on sustainable hydrogen and ammonia fuels produced from sustainable resources [2]. Unlike liquefied natural gas, these fuels do not contain carbon and produce either water or water and nitrogen as a by-product [6]. The potential of green hydrogen has particularly caught experts’ attention, which splits water using renewable energy [6]. This zero-carbon, low-cost, and scalable fuel [6] enables large international ships to voyage across the ocean on a single refuel [2]. Despite the practical barriers in the way of change, renewable hydrogen can create significant cuts in emissions and steer the shipping sector towards zero emissions by 2050 [2].

Speed optimisation

The shipping sector is a complex and multifaceted one. Hone your knowledge of the industry with ‘Shipping Business Unwrapped: Illusion, Bias and Fallacy in the Shipping Business’ (Click on the image for link).

Considering that the maritime industry burns through 300 million tonnes of fuel per year [7], conserving fuel is vital to reducing emissions [3]. Optimising speed during a ship’s journey could save 20% of its fuel with a 10% speed reduction in a single voyage [3]. However, while the process is readily applicable to new and existing vessels and somewhat easy to implement, speed optimisation may lead to economic shortfalls [3]. This is because it could reduce the cargo that ships can transport annually [3]. Instead, ships could slow steam, meaning they sail at slower speeds for part of their journey where the time allows [3]. Not only can slow steaming mitigate this economic loss, but it can maintain fuel savings [3].

Ship design

In addition to speed optimisation, ships can be designed in particular ways to help reduce fuel consumption. Presently, a range of sails, wings and rotors are being developed to install into ships as wind-assisted technologies [2]. These devices will be used either on purpose-built ships or as retrofits for existing vessels [2]. However, while this technology does optimise fuel consumption, the reported emission savings are variable [6]. Factors such as the size and type of ships can influence the effectiveness, and there are difficulties applying this technology to large vessels [2]. Still, it is projected that wind-assisted technologies could create fuel savings of 15% to 50% when coupled with route optimisation, making progress towards the zero-emissions goal [6]. As Delphine Gozillon [2], Transport and Environment‘s Sustainable Shipping Officer, explains, for “full decarbonisation, a combination of wind energy and sustainable fuels seems an ideal scenario for small and medium-size ships”.

Rotor sails are designed to use the Magnus effect for propulsion. Read more about their use in our article Rob’s Corner: Alternatives for Greener Shipping (Click on image for link).

“Wind is free, and most readily available in the ocean which is the exact reason why we are working to develop offshore wind farms. The best way to use this energy is to propel vessels directly, instead of using it to make electricity, synthesize fuels, store, transport, and burn the fuels.” – Satchel Douglas, Head of Engineering, Aloft Shipping [8].

Even though there are options to reduce maritime emissions, decarbonisation will not come about by itself [2]. Uprooting a business-as-usual scenario will require strict regulations [2] to ensure the Paris Climate Agreement target of zero emissions is met. This way, shipowners can decide which methods they find most effective to implement and ensure the decarbonisation of the international shipping sector.


[1] Transport & Environment, “Ships,” 2022. [Online]. Available: https://www.transportenvironment.org/challenges/ships/. [Accessed 13 04 2022].

[2] IRENA, A pathway to decarbonise the shipping sector by 2050, Abu Dhabi: International Renewable Energy Agency, 2021.

[3] European Commission , “Reducing emissions from the shipping sector,” [Online]. Available: https://ec.europa.eu/clima/eu-action/transport-emissions/reducing-emissions-shipping-sector_en .

[4] Zero Carbon Shipping, “Decarbonizing the global maritime industry,” 25 October 2021. [Online]. Available: https://www.zerocarbonshipping.com/. [Accessed 13 04 2022].

[5] UK Parliament Post, “International shipping and emissions,” January 2022. [Online]. Available: https://researchbriefings.files.parliament.uk/documents/POST-PN-0665/POST-PN-0665.pdf.

[6] Sustainable Shipping Initiative, “Decarbonisation: Sustainability criteria for marine fuels,” 2020. [Online]. Available: https://www.sustainableshipping.org/our-work/current-work/sustainability-criteria-for-marine-fuels/.

[7] D. Gozillon, Interviewee, Shipping Decarbonisation Article April 2022. [Interview]. 10 April 2022.

[8] S. Douglass, Interviewee, Shipping Decarbonisation Article April 2022. [Interview]. 15 April 2022.

kees torn (https://commons.wikimedia.org/wiki/File:MULTRATUG_32_&_MARGRETHE_MAERSK_(48489921962).jpg), „MULTRATUG 32 & MARGRETHE MAERSK (48489921962)“, https://creativecommons.org/licenses/by-sa/2.0/legalcode
George E. Koronaios (https://commons.wikimedia.org/wiki/File:The_container_ship_PACOBA_in_the_Saronic_Gulf_on_July_27,_2021.jpg), https://creativecommons.org/licenses/by-sa/4.0/legalcode
Wilsca (https://commons.wikimedia.org/wiki/File:Norsepower_rotor_sails_modern_version_of_flettner_rotor.jpg), https://creativecommons.org/licenses/by-sa/4.0/legalcode