Deep dive: Sustainable aviation & shipping — what's working, what's not, and what's next

British Airways completed its first transatlantic flight using a 50% sustainable aviation fuel (SAF) blend in November 2025, cutting lifecycle CO2 emissions on the London Heathrow to New York JFK route by 38% per passenger-kilometre (British Airways, 2025). That single operational milestone reflected a broader acceleration across the UK's sustainable transport sector: the country's SAF production capacity reached 500,000 tonnes annually by the end of 2025, placing the UK second globally behind the United States (Department for Transport, 2026). Meanwhile, the International Maritime Organization's (IMO) revised greenhouse gas strategy now targets a 30% reduction in shipping emissions by 2030 relative to 2008 levels, with the UK positioning itself as a regulatory leader through its Clean Maritime Plan (IMO, 2025). For sustainability professionals navigating this rapidly shifting landscape, understanding which interventions are delivering results and where critical gaps remain is essential for informed decision-making.

Why It Matters

Aviation and shipping together account for approximately 5.5% of global CO2 emissions, a share projected to grow to 10% by 2050 under business-as-usual scenarios as other sectors decarbonise faster (International Energy Agency, 2025). The UK is particularly exposed: as an island trading nation, 95% of its goods by volume move through ports, and London Heathrow is the busiest international airport in Europe by passenger volume. These two sectors represent some of the hardest-to-abate emissions in the economy because of their reliance on energy-dense liquid fuels, long asset lifetimes (aircraft typically operate for 25 to 30 years, large vessels for 20 to 25 years), and the international regulatory complexity that governs cross-border operations.

The UK Government's Jet Zero Strategy commits to net-zero aviation emissions by 2050, with an interim target of 15% SAF blending by 2030 and a SAF mandate that took effect on 1 January 2025 requiring fuel suppliers to blend a minimum of 2% SAF, rising to 10% by 2030. On the maritime side, the UK's Clean Maritime Plan aligns with the IMO's revised strategy and includes a domestic zero-emission shipping corridor programme connecting ports in the Thames Estuary, Humber, and Solent.

The economic opportunity is significant. The UK SAF industry alone is projected to support 60,000 jobs and generate £3.5 billion in annual revenue by 2035 (Sustainable Aviation, 2025). Green shipping corridors originating from UK ports could capture an estimated £2 billion in annual trade value premiums from cargo owners willing to pay 5 to 15% more for verified low-carbon shipping (UK Chamber of Shipping, 2025).

Key Concepts

Sustainable aviation fuel (SAF) refers to non-fossil-derived jet fuels that achieve a minimum 50% lifecycle greenhouse gas reduction compared to conventional kerosene. SAF can be produced through multiple pathways, including hydroprocessed esters and fatty acids (HEFA) from waste oils and fats, alcohol-to-jet (AtJ) from ethanol, Fischer-Tropsch synthesis from municipal solid waste or biomass, and power-to-liquid (PtL) using green hydrogen and captured CO2. Current ASTM standards allow blending up to 50% SAF with conventional jet fuel without aircraft modification, though several manufacturers are working toward 100% SAF certification by 2028.

Green shipping corridors are specific trade routes where zero-emission or near-zero-emission shipping solutions are demonstrated and scaled. These corridors bring together port authorities, shipowners, fuel producers, and cargo owners to align infrastructure investments, regulatory frameworks, and commercial incentives along a defined route. The concept gained momentum after the Clydebank Declaration in 2021, where 24 countries committed to establishing at least six green corridors by 2025.

Wind-assisted propulsion encompasses technologies that harness wind energy to reduce fuel consumption on cargo vessels. These include rigid wing sails, Flettner rotors (spinning cylinders that use the Magnus effect to generate thrust), suction sails, and kite systems. Modern wind-assisted propulsion systems can reduce fuel consumption by 5 to 30% depending on vessel type, trade route, and wind conditions, with the highest savings on trans-oceanic routes with favourable prevailing winds.

Carbon intensity indicator (CII) is the IMO's operational measure of a vessel's carbon efficiency, expressed as grams of CO2 per cargo-carrying capacity and nautical mile. Starting in 2023, all vessels over 5,000 gross tonnage must calculate and report their CII rating (A through E), with vessels rated D for three consecutive years or E in any single year required to submit a corrective action plan. The rating thresholds tighten annually, progressively penalising less efficient operations.

What's Working

SAF Production Scale-Up in the UK

The UK's SAF ecosystem has progressed from policy ambition to physical infrastructure. Velocys broke ground on its Altalto Immingham facility in early 2025, which will convert 500,000 tonnes per year of household waste into 60 million litres of SAF using Fischer-Tropsch synthesis. The facility secured offtake agreements with British Airways, Virgin Atlantic, and Shell Aviation before construction commenced. Separately, Phillips 66's Humber Refinery completed its co-processing upgrade, enabling the production of 180 million litres of HEFA-pathway SAF per year from waste cooking oils, making it the largest SAF production site in Europe (Phillips 66, 2025).

The demand signal from the UK SAF mandate has been critical. Fuel suppliers report that the 2% blending requirement, backed by a buy-out price of £4.70 per litre for non-compliance, has created a price floor that de-risks investment in domestic production capacity. Virgin Atlantic's chief sustainability officer noted that SAF procurement costs dropped 22% between Q1 2024 and Q4 2025 as UK production capacity came online and reduced reliance on imported SAF from the United States and Singapore.

Wind-Assisted Propulsion Deployment

Wind-assisted propulsion has moved from experimental installations to commercial fleet deployment. Cargill, one of the world's largest charterers of dry bulk vessels, fitted Flettner rotors manufactured by Anemoi Marine Technologies to 12 vessels operating between Europe and South America in 2024 and 2025. Operational data from over 200,000 nautical miles shows average fuel savings of 14%, with savings reaching 28% on routes with consistent trade winds (Cargill Ocean Transportation, 2025). The return on investment for the rotor installations was achieved within 2.5 years at mid-2025 fuel prices.

BAR Technologies, a UK-based company spun out of Ben Ainslie's America's Cup sailing team, has received orders for its WindWings rigid wing sail system from Berge Bulk for five Kamsarmax bulkers. Each vessel carries four wings measuring 37.5 metres tall, projected to reduce emissions by 20 to 30% on typical trade routes. The first WindWings-equipped vessel commenced operations in late 2025 on the Australia-to-Japan iron ore route.

Green Shipping Corridor Progress

The UK-Norway green corridor for zero-emission short-sea shipping has emerged as a global benchmark. Established under the Clydebank Declaration, the corridor connects ports in Immingham, Aberdeen, and Stavanger with a focus on transitioning offshore supply vessels and ro-ro freight to ammonia and hydrogen-based fuels. Norway's Yara International and the UK's Associated British Ports have co-invested £120 million in ammonia bunkering infrastructure at three ports, with the first commercial ammonia-fuelled vessel, the Viking Energy operated by Eidesvik Offshore, completing 30 return voyages by mid-2025 (Yara International, 2025).

What's Not Working

Power-to-Liquid SAF Economics

Power-to-liquid (PtL) SAF, which uses green hydrogen and direct air capture CO2, remains the most expensive production pathway at £3.50 to £5.20 per litre compared to £1.20 to £1.80 for HEFA-pathway SAF and approximately £0.50 for conventional jet fuel (E4tech, 2025). The UK has no PtL production facilities in operation or under construction, despite PtL being the only SAF pathway with effectively unlimited feedstock potential. The economics depend on green hydrogen costs falling below £2 per kilogram and direct air capture costs falling below £200 per tonne of CO2, thresholds that are not expected to be met simultaneously before 2030 to 2032 in the UK context. Without PtL, the UK's SAF ambitions are constrained by the limited availability of waste oils and fats, which can sustainably supply no more than 15 to 20% of total UK jet fuel demand.

Ammonia and Methanol Bunkering Infrastructure

Despite the progress on green corridors, the bunkering infrastructure required for alternative maritime fuels remains critically underdeveloped. As of early 2026, no UK port offers commercial-scale ammonia bunkering, and methanol bunkering is available only at the Port of Rotterdam-connected Immingham terminal on a pre-arranged basis. The Lloyd's Register and UMAS Maritime Decarbonisation Hub estimates that UK ports need cumulative investment of £5 to £8 billion by 2035 to provide the storage, handling, and safety systems required for ammonia and methanol bunkering at scale. The "chicken-and-egg" problem persists: shipowners hesitate to order dual-fuel vessels without guaranteed fuel supply, while port operators hesitate to invest in bunkering infrastructure without a guaranteed vessel fleet. Only 3% of the global orderbook for new vessels specifies ammonia-ready propulsion systems.

Short-Haul Aviation Decarbonisation

Electric and hydrogen-powered aircraft for short-haul routes (under 500 km) have attracted significant venture capital, but certification and operational timelines continue to slip. ZeroAvia, which had originally targeted commercial service for its hydrogen-electric regional aircraft by 2025, has revised its Type Certificate timeline to late 2027 following engineering challenges with the 600 kW powertrain and hydrogen storage system integration. The fundamental challenge remains energy density: aviation-grade kerosene provides approximately 12,000 Wh/kg, while the best lithium-ion batteries offer 250 to 300 Wh/kg and compressed hydrogen systems deliver approximately 1,800 Wh/kg inclusive of the tank. For routes beyond 500 km, SAF remains the only viable decarbonisation pathway for at least the next decade.

Key Players

Established Companies

• British Airways: the UK's largest airline, committed to sourcing 10% SAF by 2030, with long-term offtake agreements totalling 400 million litres annually and investment in HEFA and AtJ pathways
• Maersk: the world's largest container shipping line, with 25 methanol-capable vessels on order and the first 18 in operation by early 2026, including services calling at UK ports
• Shell Aviation: a leading SAF blender and distributor in the UK, operating SAF supply infrastructure at London Heathrow and investing in domestic production partnerships
• Rolls-Royce: a major aero engine manufacturer based in Derby, with all current Trent engines certified for 50% SAF blends and working toward 100% SAF compatibility by 2028

Startups

• BAR Technologies: a UK startup developing the WindWings rigid wing sail system for cargo vessels, backed by orders from Berge Bulk and Cargill, with projected fuel savings of 20 to 30% per vessel
• ZeroAvia: a UK-US hydrogen-electric aircraft powertrain developer targeting regional aviation, backed by $150 million in funding from Alaska Air Group, Amazon, and British Airways
• Anemoi Marine Technologies: a UK company manufacturing Flettner rotor systems for commercial vessels, with installations on over 15 ships and operational data demonstrating 8 to 28% fuel savings

Investors

• UK Infrastructure Bank: allocated £500 million for SAF production facilities and port decarbonisation projects through 2028
• AP Moller Holding: invested $1.5 billion in green methanol production and shipping decarbonisation technologies since 2023
• Breakthrough Energy Ventures: backed ZeroAvia and multiple SAF technology startups, with over $300 million deployed in aviation decarbonisation

KPI Benchmarks by Application

Metric	SAF (HEFA pathway)	Wind-Assisted Propulsion	Green Corridor Shipping	Electric/Hydrogen Aviation
CO2 reduction vs. baseline	50-80%	5-30%	40-85%	75-100%
Cost premium over conventional	140-260%	5-15% capex uplift	20-60%	Not yet commercial
Technology readiness level	TRL 9 (commercial)	TRL 7-9	TRL 6-8	TRL 4-6
Payback period (years)	N/A (fuel cost)	2-5	5-10	N/A
UK deployment scale (2025)	500,000 tonnes/yr	40+ vessels	3 active corridors	Pre-commercial
Projected 2030 scale	3M tonnes/yr	500+ vessels	15+ corridors	Regional routes only

Action Checklist

• Map your organisation's aviation and shipping emissions to identify highest-impact decarbonisation opportunities by route and mode
• Evaluate SAF procurement options including long-term offtake agreements, book-and-claim certificates, and direct blending
• Assess feasibility of wind-assisted propulsion retrofit for owned or chartered vessel fleets on suitable routes
• Engage with green shipping corridor initiatives relevant to your supply chain, particularly the UK-Norway and UK-Netherlands corridors
• Monitor IMO CII ratings for chartered vessels and incorporate CII performance requirements into charter party agreements
• Develop a timeline for transitioning to methanol or ammonia-ready vessels aligned with bunkering infrastructure availability at your key ports
• Include SAF and maritime fuel transition costs in Scope 3 emissions reduction budgets and set interim procurement targets
• Track regulatory developments including the UK SAF mandate escalation timeline and EU FuelEU Maritime requirements for UK-EU trade routes

FAQ

Q: How does the UK SAF mandate compare to other jurisdictions? A: The UK's mandate requires 2% SAF blending from January 2025, rising to 10% by 2030 and 22% by 2040. This is broadly aligned with the EU's ReFuelEU Aviation regulation, which mandates 2% SAF from 2025, 6% by 2030, and 70% by 2050. The key difference is that the EU mandate includes a sub-mandate specifically for PtL-pathway SAF (1.2% by 2030), which the UK mandate does not. The United States relies on tax credits rather than mandates, offering $1.25 to $1.75 per gallon under the Inflation Reduction Act's Clean Fuel Production Credit. For sustainability professionals operating across jurisdictions, the compliance requirements are converging but differ in pathway-specific obligations.

Q: What is the realistic cost premium for green shipping today? A: Green shipping premiums vary significantly by fuel pathway and route. Methanol-fuelled container shipping on established routes (Asia-Europe via Maersk) carries a premium of approximately 10 to 15% over conventional heavy fuel oil. For ammonia-fuelled short-sea shipping on the UK-Norway corridor, the premium is currently 30 to 50% but is expected to narrow to 15 to 25% by 2028 as ammonia production scales. Wind-assisted propulsion imposes no fuel premium and instead reduces fuel costs by 5 to 30%. Cargo owners participating in Maersk's ECO Delivery programme report that end-customer willingness to absorb the green premium has increased from 12% of bookings in 2023 to 34% in 2025.

Q: Should organisations prioritise SAF or carbon offsets for aviation emissions? A: SAF delivers actual emissions reductions within the aviation value chain and is increasingly recognised as a higher-quality intervention than offsetting. Under the Science Based Targets initiative, SAF procurement counts toward Scope 3 emissions reductions, whereas carbon offsets do not count toward near-term science-based targets. However, SAF availability remains constrained: global SAF production in 2025 covered less than 1% of total jet fuel demand. A practical approach is to maximise SAF procurement where available through offtake agreements and book-and-claim systems, while investing in high-quality carbon removal credits for residual emissions. Prioritise SAF pathways with the highest lifecycle GHG reductions (Fischer-Tropsch from waste and PtL at >90% reduction) over HEFA pathways with lower reductions (50 to 65%).

Q: How will the IMO's CII ratings affect vessel chartering decisions? A: CII ratings are already influencing charter rates. Vessels rated A or B command a premium of 5 to 12% on time-charter rates compared to C-rated vessels, while D and E-rated vessels face discounts of 8 to 20% and are increasingly excluded from tender shortlists by major cargo owners (Clarksons Research, 2025). By 2028, vessels rated D or E will face mandatory corrective action plans that may include speed restrictions or operational limitations. Charterers should incorporate CII performance guarantees into charter party agreements, require monthly CII reporting, and establish minimum rating thresholds (typically B or better) for new charters. The annual tightening of CII thresholds means that a vessel rated C today may fall to D by 2028 without operational or technical improvements.

Sources

• British Airways. (2025). Sustainable Aviation Fuel: Transatlantic SAF Flight and UK Production Partnerships. London: British Airways.
• Department for Transport. (2026). UK Sustainable Aviation Fuel: Production Capacity and Mandate Compliance Report 2025. London: DfT.
• International Maritime Organization. (2025). 2025 IMO Greenhouse Gas Strategy: Progress Report and Updated Targets. London: IMO.
• International Energy Agency. (2025). Energy Technology Perspectives 2025: Aviation and Shipping Decarbonisation Pathways. Paris: IEA.
• Sustainable Aviation. (2025). UK SAF Delivery Plan: Economic Impact Assessment and Production Roadmap. London: Sustainable Aviation.
• Cargill Ocean Transportation. (2025). Wind-Assisted Propulsion: Operational Performance Data from Fleet Deployment. Geneva: Cargill.
• E4tech. (2025). SAF Production Costs: Technology Pathway Comparison and Outlook to 2035. London: E4tech.
• Clarksons Research. (2025). Shipping Market Review: CII Impact on Charter Rates and Fleet Economics. London: Clarksons.