The ocean has carried human commerce for millennia. Today, roughly 90% of global trade moves by sea — approximately 11 billion tonnes of cargo annually, according to the United Nations Conference on Trade and Development (UNCTAD). But this invisible backbone of globalisation comes at a steep environmental price. The international shipping industry is responsible for nearly 3% of global greenhouse gas (GHG) emissions, a figure the International Maritime Organization (IMO) warns could surge to 17% by 2050 if left unchecked.
That warning has sparked one of the most ambitious industrial transformations underway anywhere on earth.
The Scale of the Problem
To appreciate why shipping is a hard nut to crack, consider the numbers. A single ultra-large container vessel (ULCV) like the Ever Ace — operated by Evergreen Marine and capable of carrying 23,992 TEUs (twenty-foot equivalent units) — burns roughly 250 tonnes of heavy fuel oil (HFO) per day at sea. HFO is the residual sludge left after crude oil refining, and it contains up to 2,500 times more sulphur than road diesel. When burned, it emits sulphur oxides (SOₓ), nitrogen oxides (NOₓ), particulate matter, and carbon dioxide in quantities that dwarf most land-based industries.
The IMO’s 2020 Sulphur Cap — formally MARPOL Annex VI Regulation 14 — slashed the permissible sulphur content in marine fuel from 3.5% to 0.5%, forcing carriers to either switch to low-sulphur fuel oil (LSFO), install exhaust gas cleaning systems (scrubbers), or pivot to cleaner alternative fuels. It was a significant regulatory moment, but it barely scratched the carbon problem.
The IMO 2023 Strategy: A Defining Commitment
In July 2023, the IMO revised its GHG strategy with considerably more teeth. The new framework targets net-zero GHG emissions from international shipping by or around 2050, with checkpoints requiring at least a 20% (striving for 30%) reduction in total GHG emissions by 2030 compared to 2008 levels, and at least 70% (striving for 80%) by 2040.
Critically, the strategy introduces the concept of the “basket of measures” — a mix of carbon intensity indicators (CII), the Energy Efficiency Existing Ship Index (EEXI), and future economic measures like a carbon levy. The CII, which came into force on 1 January 2023, requires all vessels above 5,000 GT to calculate and report their annual carbon intensity and receive a rating from A (best) to E (worst). Ships rated D or E for three consecutive years must submit a corrective action plan.
This is not merely paperwork. A ship with poor CII ratings can face charter restrictions, port-state scrutiny, and financing difficulties in an era where ESG (Environmental, Social, and Governance) criteria are reshaping access to capital.
Alternative Fuels: The Race for the “Silver Bullet”
No single fuel has emerged as the universal solution, giving rise to what industry analysts at DNV term the “multi-fuel future.”
Liquefied Natural Gas (LNG) has seen the broadest early adoption. CMA CGM, the French container giant, operates a fleet of over 30 LNG-powered vessels and has contracted for more. LNG reduces CO₂ emissions by roughly 20–25% compared to HFO on a tank-to-wake basis. However, methane slip — uncommitted methane venting from engines — partially erodes this benefit on a well-to-wake lifecycle basis, a concern that remains technically active.
Methanol is gaining significant traction. Maersk, the world’s second-largest container line by capacity, accepted delivery of the Laura Mærsk in 2023 — the world’s first large container vessel capable of running on green methanol. The ship’s MAN B&W ME-LGIM dual-fuel engine can operate on both conventional fuel and methanol. Maersk has since ordered 25 more methanol-ready vessels. The appeal lies in methanol’s liquid state at ambient temperatures (requiring less complex cryogenic infrastructure than LNG or liquid hydrogen) and its potential for genuinely carbon-neutral production via renewable electricity and captured CO₂.
Ammonia is viewed by many naval architects and fuel chemists as the most promising long-term vector, since it contains no carbon whatsoever. Japan’s NYK Line and MAN Energy Solutions are jointly developing ammonia-fuelled two-stroke engines, with commercial deployment targeted for the mid-2020s. The challenges are significant — ammonia is toxic, requires careful handling protocols under the IGC Code, and its combustion produces NOₓ — but its volumetric energy density and established production infrastructure (via the Haber-Bosch process, ideally powered by renewables) make it compelling.
Hydrogen, while theoretically perfect, faces the most severe infrastructural and energy density barriers. Liquid hydrogen must be stored at –253°C, demanding insulated cryogenic tanks that consume disproportionate cargo space.
Wind-Assisted Propulsion: Old Technology, New Ambition
The industry is also revisiting something ancient: wind. Wind-Assisted Ship Propulsion (WASP) technologies — rotor sails, rigid wing sails, and kite systems — are being retrofitted onto existing vessels with measurable results.
Cargill, one of the world’s largest commodity traders, partnered with BAR Technologies to install a WindWings system — 37.5-metre rigid composite wing sails — aboard the bulk carrier Pyxis Ocean in 2023. Sea trial data published in early 2024 showed fuel savings averaging around 11% over a transatlantic voyage, with peaks above 30% on favourable wind routes. At scale across a global bulk fleet, such savings translate to millions of tonnes of CO₂ annually.
Norsepower’s Rotor Sails — large vertical cylinders that exploit the Magnus effect to generate thrust — have been installed on vessels operated by Viking Line, Maersk Tankers, and Anglo-American’s ore carriers. The technology requires no crew training changes, produces no emissions of its own, and can be retrofitted without drydocking in some configurations.
Port Decarbonisation: The Shoreside Equation
Ships spend a surprising fraction of their operating hours at berth, engines running to power onboard systems. Cold ironing — or shore power / Alternative Maritime Power (AMP) — allows vessels to plug into the port’s electrical grid and shut down auxiliary diesel generators.
The Port of Los Angeles, handling over 9 million TEUs annually, has one of the world’s most advanced shore power networks, with over 90% of container vessels using AMP at berth as a regulatory requirement under the California Air Resources Board (CARB) framework. The Port of Rotterdam — Europe’s largest — is rapidly expanding its shore power grid as part of its commitment to becoming a carbon-neutral port by 2050, including hydrogen bunkering infrastructure for early-mover vessels.
Finance and the ESG Imperative
Capital flows are increasingly restructuring the incentive architecture. The Poseidon Principles, signed by over 30 major maritime lenders representing more than $250 billion in shipping finance, commit signatories to aligning their loan portfolios with the IMO’s decarbonisation trajectory. Banks including Citi, Société Générale, and DNB now require borrowers to disclose and improve the climate alignment of their fleets, with non-compliant vessels facing potential financing restrictions or higher borrowing costs.
The European Union’s extension of the Emissions Trading System (EU ETS) to maritime transport from 2024 adds a direct carbon price to voyages into, out of, and within EU ports. Ships must surrender ETS allowances (EUAs) for 50% of emissions on extra-EU voyages and 100% on intra-EU voyages, with the share rising over time. This creates a quantifiable financial penalty for carbon-intensive operations and directly improves the economics of alternative fuels.
The Road — or Sea — Ahead
Shipping’s decarbonisation is neither simple nor cheap. The Energy Transitions Commission estimates the additional investment required to decarbonise shipping by 2050 at roughly $1–1.4 trillion, predominantly in fuel production, bunkering infrastructure, and newbuild vessels. For an industry that operates on thin margins and 25-year asset lifetimes, the transition demands unprecedented coordination between shipowners, charterers, fuel producers, port authorities, and regulators.
Yet the direction is irreversible. The combination of tightening IMO regulations, the EU ETS, growing cargo-owner ESG requirements, and the accelerating economics of green fuels means the age of cheap, dirty bunker fuel is drawing to a close — perhaps faster than many expected.
The sea doesn’t change. But the ships sailing it are beginning to.
References: IMO GHG Strategy 2023; MARPOL Annex VI; DNV Energy Transition Outlook 2023; Maersk Sustainability Report 2023; BAR Technologies WindWings Sea Trial Data 2024; Poseidon Principles Framework; EU ETS Maritime Regulation 2023; UNCTAD Review of Maritime Transport 2023.
