Why Shipping Is the Hardest Decarbonisation Problem in Transport
International shipping transports approximately ninety percent of global trade by volume and accounts for roughly three percent of global greenhouse gas emissions. Decarbonising shipping presents a combination of technical, economic, and regulatory challenges that make it arguably the most difficult emissions reduction problem in the transport sector. Aviation shares some of shipping's challenges but operates in a more concentrated regulatory environment and over shorter ranges than the largest container ships and bulk carriers whose trans-oceanic voyages require energy storage densities that no current zero-emission technology can match at acceptable cost. Road transport's decarbonisation is well advanced through electrification whose technology is mature and whose cost trajectory is well-established. Shipping's decarbonisation has no equivalent clear technical pathway. The energy density of the fuel required to propel a 20,000 TEU container ship across the Pacific Ocean exceeds what battery technology can provide by several orders of magnitude, and the alternative fuels whose energy density is sufficient, including ammonia, methanol, and hydrogen, each present their own cost, safety, and infrastructure challenges whose resolution requires investment and coordination across the entire maritime fuel supply chain.
The International Maritime Organization's revised greenhouse gas strategy, adopted in 2023, established targets for international shipping to reach net zero emissions by or around 2050, with indicative milestones requiring a twenty percent reduction in emissions intensity by 2030 and at least seventy percent by 2040. These targets are creating the regulatory certainty that ship operators, shipbuilders, and fuel suppliers need to make investment decisions about the technologies and fuels that will characterise the shipping fleet of the 2030s and beyond. The commercial consequence is a maritime industry that is investing in alternative fuel vessels at a pace that would have been difficult to predict three years ago, driven by the combination of IMO regulatory pressure, the Carbon Intensity Indicator requirements that are already affecting the commercial operation of existing vessels, and the customer pressure from major cargo owners whose scope 3 emissions commitments include the shipping of their products.
Alternative Fuels and the Infrastructure Race
Methanol has emerged as the near-term alternative fuel attracting the most shipbuilding orders, driven by the ordering activity of Maersk, which has committed to methanol-fuelled vessels as part of its net-zero pathway and has placed orders for a large fleet of methanol dual-fuel container ships. Methanol's commercial advantages over other alternative fuels include its liquid form at ambient temperature, which allows storage in conventional tank configurations without the cryogenic or pressurised containment that LNG, hydrogen, and ammonia require, and the existing commercial production base that gives methanol fuel availability at more ports than the other alternative fuels. The limitation is that current methanol production is primarily grey methanol whose carbon footprint is similar to conventional marine fuel. Green methanol, produced from renewable electricity and captured carbon dioxide, or bio-methanol from sustainable biomass, has the low carbon footprint that IMO targets require but is available in very limited volume at very significant cost premiums over grey methanol.
Ammonia is the alternative fuel attracting the most interest for the largest ship types whose long-range operation requires the energy density that methanol cannot provide at the volumes that practical tank sizes accommodate. Ammonia's energy density by volume is lower than conventional marine fuel but higher than methanol, and green ammonia whose hydrogen content is derived from renewable electrolysis is the zero-carbon fuel candidate that most large-ship decarbonisation pathways converge on for the deep-sea shipping segment. The challenges are the toxicity of ammonia that requires safety systems beyond those needed for conventional or methanol fuels, the immaturity of ammonia engine technology for the two-stroke engines that power large ships, and the near-complete absence of ammonia bunkering infrastructure at major shipping ports.
Wind Assist and Operational Efficiency
The commercial deployment of wind assist technology on commercial vessels, which can reduce fuel consumption and emissions from existing ships without fuel switching, is the maritime decarbonisation approach with the most immediate commercial return for existing fleet operators whose vessels are not yet ready for alternative fuel conversion. Rotor sails, rigid wing sails, and kite systems that harvest wind energy to supplement the main engine propulsion are being retrofitted to and specified on new tankers, bulk carriers, and container ships. The fuel savings that wind assist provides depend on the route, the wind conditions encountered, and the vessel type, but commercially documented savings of five to fifteen percent on fuel-intensive bulk carrier and tanker routes represent a commercial return that justifies the capital investment at current bunker fuel prices and carbon intensity requirements.
Top 10 Companies in Maritime Decarbonisation Globally
- Maersk: The most commercially committed major shipping line in maritime decarbonisation; its fleet of methanol dual-fuel vessels, green methanol offtake agreements, and its stated target of carbon-neutral operations by 2040 make it the reference case for how a major shipping operator can commercially commit to decarbonisation ahead of regulatory requirements.
- MAN Energy Solutions: Marine engine manufacturer developing ammonia and methanol engines for commercial shipping; its two-stroke ammonia engine development and its methanol retrofit kits for existing MAN engines are the products that determine how quickly the installed fleet of large ships can transition to alternative fuels.
- Wartsila: Marine technology company with engine, fuel system, and vessel management technology for alternative fuel vessels; its four-stroke ammonia engine development and its LNGPac and MethanolPac fuel containment systems are the enabling technologies for alternative fuel adoption across the medium-speed engine segment that Wartsila dominates.
- ClassNK / Lloyd's Register: Ship classification societies whose approval of alternative fuel vessel designs and whose safety standards for ammonia and methanol handling determine the regulatory framework within which alternative fuel vessels are built and operated; their technical requirements shape the engineering specifications of every alternative fuel vessel under construction.
- Norsepower: Finnish rotor sail manufacturer whose Rotor Sail technology is the most commercially deployed wind assist system for commercial shipping; its installations on tankers, car carriers, and cruise ships provide the operational performance data that demonstrates the commercial viability of wind assist across diverse vessel types and trade routes.
- Airseas: Airbus spin-out developing the Seawing automated kite system for cargo vessel wind assistance; its aerospace engineering approach to kite design and autonomous operation and its Airbus heritage create the technology credibility that novel maritime technology concepts require to attract shipping company investment.
- Yara Clean Ammonia: Yara's green ammonia business developing production, distribution, and bunkering infrastructure for shipping; its fertiliser production heritage creates the ammonia supply chain expertise and production infrastructure that green ammonia for shipping requires, making it the natural anchor of the maritime ammonia fuel supply chain.
- HH2E / Ørsted: Green hydrogen and ammonia production developers with maritime fuel supply as a target offtake market; their renewable energy access and production development experience position them as the fuel suppliers that shipping companies will need to contract with to secure green fuel volumes for their alternative fuel vessel fleets.
- Kongsberg Maritime: Norwegian maritime technology company with vessel automation, energy management, and hybrid propulsion systems; its vessel energy management software that optimises fuel consumption across conventional and alternative fuel systems is the operational technology that maximises the commercial return on alternative fuel vessel investment.
- Shell Shipping and Maritime: Energy major with LNG bunkering infrastructure and green fuel development programmes; its LNG bunkering network, methanol supply development, and biofuel blending programmes make it the fuel supplier with the broadest alternative fuel portfolio for the shipping industry, even as the company navigates its own complex decarbonisation transition.