The future of a clean and sustainable shipping industry

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The shipping industry and climate change

Accounting for about 80% of the global goods trade, the international shipping industry is essential to world trade, with a projected 4.8% growth in 2021 (1-3). Greenhouse gas (GHG) emissions by the shipping industry account for  2-3% of global GHG emissions yearly; if it were a country, the international shipping industry would be the 7th biggest GHG emitter on the planet (4-6). Furthermore, the industry relies on heavy fuel oil (HFO) - a cheap fossil-based fuel. HFO combustion also releases sulfur oxides (SOx), which are harmful to both health (7) and the environment (8). This has led the International Maritime Organization to implement the 2020 Sulfur Cap regulation and 2050 carbon neutrality goal (4,8).

An engineering approach is effective but limited

Increased fuel efficiency and operationl optimisation have led to a 33% reduction in annual CO2 emissions from the shipping industry since 2007 (9). Some exemplary measures for fuel efficiency involve upgraded propulsion (c.a .20% fuel saving) (10) and efficient ship design (CMA-CGM’s bulbous bows design reduced CO2 emissions by 5-10% (11)). Meanwhile, reductions in CO2 emissions via operational optimisation have largely been achieved by the ‘slow steaming’ of ships (a 19% CO2 saving with a 10% reduction in ship speed) (12), ship maintenance (15) and optimal route planning (9,11,13). Notably, APM-Maersk achieved a 42% reduction in CO2 emissions with route-network optimisation and waste heat recovery (13). However, whilst they successfully reduce operating expenditure (9), these solutions do not fully address GHG emissions from fuel combustion itself, which still accounts for 1-2% of global GHG emissions (4,6,8).

Alternative liquid fuels: An imperfect but practical way to lower GHG emissions

Marine Gas Oil (MGO) is commonly used to stay within the sulfur emissions limit, but this does not address the GHG emissions issue (8,16). Alternative fuel sourcing is pivotal.  For example, the use of green liquified natural gas (LNG) in place of fossil-LNG reduces GHG emissions by almost 50% (17). However, methane leaks from green LNG usage are problematic, as methane is 30 times more potent a GHG than CO2 (13). LNG also requires a high initial investment, but is cheaper than heavy fuel oil in the long run (18). Encouragingly, the world’s first (and largest) LNG-powered container ship was revealed in 2019, signifying increased appetite for greener fuel solutions (11).

Biodiesels are practical alternative fuels that can reduce GHG emissions by 80% in comparison to fossil fuels (11,14,16). For example, biodiesel was recently deployed for the Rotterdam-Shanghai route, where it reduced CO2 emissions by 85% (13). However, there are some concerns regarding engine compatibilities, life-cycle analysis and the supply-consumption imbalance of biodiesel fuel that need to be addressed if biodiesel is to be adopted into the shipping industry (11,14,16).

Significant reductions in GHG emissions can also be achieved with green methanol sourced from carbon capture, though securing sustainable methanol feedstock can be challenging (13,14,17,19). Despite the lower overall investment in methanol compared to other green alternatives, there are several methanol-fuelled ships currently under development (14,17,19).

Ammonia is a carbon-free (19), scalable and renewable alternative fuel, but has drawbacks of toxicity, NOx emissions and poor engine performance (14). Currently, a dual-fuel concept (LNG-ammonia) is under development as a viable solution to adopt ammonia in the industry (14).

In addition, the adoption of green hydrogen (carbon-free) fuel cells in shipping can significantly reduce GHG emissions (19). Its limitations as a fuel source, however, stem from its fuel storage requirements and associated infrastructure costs (19). As a result, the current power capacity of hydrogen fuel cell ships is still relatively small (14). An alternative means of utilising hydrogen is to consider hydrogen as a precursor of other renewable fuels such as methanol, ammonia and LNG (14).

Figure 1. Well-to-propeller GHG emission of fossil-based and renewable-based fuels[14,15]. HFO = Heavy fuel oil; MGO = Marine gas oil; LNG = Liquified natural gas; LUC = Land use change; LH2 = Liquified hydrogen.

Electrification of ships is feasible but challenging

Full electrification of ships can reduce GHG emissions by up to 48% compared with conventional fuel-engine systems. Electrified ships are also more efficient, have lower maintenance costs and produce less noise (3,14,20). However, full electrification is currently feasible only in smaller ships (such as ferries), with container ships remaining under trial (13,14,20,21). Despite falling Li-Ion battery prices and increasing capacity, electrification would need to be 10-20 times more efficient to be practical in container ships, with solid-state batteries anticipated to be the next breakthrough development (3).

The cost of electrification is high, however, with ferry electrification incurring a 40% increase in Capital Expenditure (20). An alternative is to employ a hybrid system with power-optimisers, a load-demand manager and storage capacity for green energy generated onboard. This can result in a 20% fuel saving and a 57% increase in engine efficiency (10,20). For example, green electricity generated from wind turbines mounted on ships can be stored and used onboard with power production optimisation (22). A drawback is that the propulsion power supplied from purely stored energy is limited to a very short-range operation or an emergency period (14).


There are numerous promising solutions to realise a clean and sustainable future for the shipping industry. However, the competitive economic gap between traditional and sustainable solutions needs to be closed as the industry tends to favour mature, cheaper and established solutions (3,13,20). Hence, policymakers should look to develop and implement policies that incentivise and support sustainable solutions through carbon levies and subsidies for green fuels, creating a level playing field for industry players pioneering green solutions.


1: United Nations Conference on Trade and Development. "Review of Maritime Transport 2020". Accessed 23 Febuary 2021.

2: European Community Shipowners' Associations. "Shipping and Global Trade: Towards an EU external shipping policy". Accessed 23rd Febuary 2021.

3. The Motorship. "Looking ahead to renewable fuels". Accessed 23rd Febuary 2021.

4: International Energy Agency. "Tracking transport 2020". Accessed 23rd Febuary 2021.

5: European Commission. "Reducing emissions from the shipping sector". Accessed 23rd August 2021.

6: EDGAR. "Fossil CO2 emissions of all world countries, 2020 report". 30th October 2017.

7: Sofiev, Mikhail. et al. "Cleaner fuels for ships provide public health benefits with climate tradeoffs". Nature Communications, Volume 9. 2018.

8: International Maritime Organisation. "IMO 2020 – cutting sulphur oxide emissions". 2020.

9: Cariou, Pierre. et al. "Towards low carbon global supply chains: A multi-trade analysis of CO2 emission reductions in container shipping". International Journal of Production Economics, Volume 208, Pages 17-28. Febuary 2019.

10. Nuchturee, Chalermkiat. et al. "Energy efficiency of integrated electric propulsion for ships – A review". Renewable and Sustainable Energy Reviews, Volume 134. December 2020.

11: CMA CGM Group. "Our sustainability approach". 2019.

12: Transport and Environment. "Shipping and climate change". 2020.

13. Maersk. "Sustainability Report 2019". 2019.

14: Maritime Energy and Sustainable Development Centre of Excellence. "A study on the future energy options of Singapore harbour craft". Nanyang Technological University, 2020. Report-A Study on the Future Energy Options of Singapore Harbour Craft.pdf.

15: Maritime Energy and Sustainable Development Centre of Excellence. "Alternative fuels fo international shipping". Nanyang Technological University, 2020.

16: The MSC Group. "MSC Sustainability Report 2019". 2019.

17: Liu, Ming. et al. "Is methanol a future marine fuel for shipping?". Journal of Physics, Volume 1357, 2019.

18: Hoang, Anh Tuan and Pham, Van Viet. "Technological Perspective for Reducing Emissions from Marine Engines", International Journal on Advanced Science, Volume 9, Issue 6, 2019.

19: Maritime Energy and Sustainable Development Centre of Excellence. "Feasibility Study of Hydrogen as Fuel for PSV Applications". Nanyang Technological University, 2019.

20: Maritime Energy and Sustainable Development Centre of Excellence. "Electrification of Singapore harbour craft". Nanyang Technological University, 2020. Report-Electrification of Singapore Harbour Craft-Shore and Vessel Power System Considerations.pdf.

21: Rivera. "Breathing life into Yara Birkeland". 2019.

22: Paulson, Midhu and Chacko, Marianna. "Integrating wind electrical energy for the marine electrical power system" International Journal of Innovative Technology and Exploring Engineering, Volume 9, Issue 1, 2019.

PhD Student in Chemical Engineering at University of Cambridge, UK
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