Short answer up front: using liquefied natural gas (LNG) instead of heavy fuel oil (HFO)/VLSFO can cut tail-pipe CO₂ and air-pollutant emissions by roughly 15–25% on a tank-to-wake basis for modern engines — but upstream methane emissions and methane “slip” in engines can erase much or all of that climate benefit if they’re not tightly controlled.
The real climate outcome depends on engine type, fuel supply chain leakage, the time-horizon you use (20-year vs 100-year GWP), and policy/infrastructure action to curb methane. I’ll walk through the numbers, the current uptake, and pragmatic next steps.
When burned, LNG (mostly methane) produces far lower sulphur oxides and particulates than HFO and also reduces NOx and CO₂ per unit of energy:
SOx & PM: LNG is essentially sulfur-free, so SOx and particulate emissions drop ≈90–99% compared with HFO, benefitting port and coastal air quality.
NOx: NOx falls substantially with modern gas engines and after-treatment options, though exact reduction depends on engine tuning and exhaust treatment.
These air-quality improvements are why ports and liner operators favour LNG for vessels that call frequently in populated areas.
There are two different comparisons to keep clear:
Tank-to-wake (TtW) — CO₂ produced by combustion onboard.
Well-to-wake (WtW) — TtW + upstream supply chain emissions (fuel production, liquefaction, transport), including methane leaks.
Typical ranges from peer studies and industry analyses:
TtW CO₂: LNG engines (especially 2-stroke slow-speed and some modern dual-fuel designs) commonly show ~18–28% lower CO₂ emissions than HFO on a tank-to-wake basis for the same propulsion work.
WtW (net climate) outcomes: When upstream methane and engine methane slip are included, net WtW GHG reductions typically shrink to a single-digit percentage or, in some estimates, disappear entirely — results range from a small net benefit to a net penalty depending on assumptions. Conservative academic estimates show maximum lifecycle benefit ≈15% (100-yr GWP) under best-case methane control, while industry studies report up to ~23% WtW reduction under favourable conditions (low supply leaks, advanced engines).
Why results vary so much: methane is a powerful short-lived greenhouse gas. Using the IPCC AR6 metrics, 1 tonne of methane ≈ 81× CO₂ over 20 years (GWP₍20₎) or ≈28–30× over 100 years (GWP₍100₎) — so modest methane emissions can overwhelm CO₂ savings, especially on near-term (20-year) horizons.
Two methane sources matter:
Engine methane slip: unburned methane exhausted from the engine. Measured slip varies with engine technology; a consolidated study found average measured slip ~3.8% across engines, with a wide spread by engine type. At that level, methane slip materially reduces or negates LNG’s climate advantage on a 20-year horizon.
Upstream (supply chain) methane leaks: from production, processing and liquefaction. Recent global assessments show these can be substantial but also largely reducible: the IEA estimates LNG supply emissions could be cut by >60% with today’s technologies, and cutting methane leaks is the single largest lever.
Bottom line: control both slip and supply leakage and LNG gives consistent climate benefits; fail to control them and LNG can become worse than low-sulphur fuel oil over short horizons.
The fleet is growing fast:
DNV reported 641 LNG-powered ships in operation at end-2024, with record deliveries (169) in 2024 and an orderbook that could double LNG numbers by the end of the decade.
Industry coalition SEA-LNG puts active LNG vessels at >2% of the global fleet, rising to ~4% by vessel numbers or ~6% by DWT once the orderbook is included; many large container operators are switching to LNG-capable newbuilds (large orders from MSC, CMA CGM, Maersk, Hapag-Lloyd).
Bunkering infrastructure: LNG bunkering availability in ~198 ports worldwide and dozens of LNG bunker vessels are now operating — infrastructure is expanding but remains uneven geographically.
Market commentary expects LNG bunker volumes and dual-fuel vessel orders to continue rising as owners prepare for upcoming regulatory and carbon-intensity metrics.
Think of LNG as a transition / bridging fuel that can deliver air-quality wins immediately and climate wins if two conditions are met:
Technology choice on ships — high-pressure, low-slip engine designs and methane-abatement hardware (oxidation catalysts, aftertreatment) should be specified at build. Proper fuel-handling and tank design reduce boil-off and slippage.
Supply-chain mitigation — rigorous measurement, monitoring and abatement of methane upstream (leak detection & repair, reduced flaring, best practices in liquefaction and transport). The IEA shows most supply reductions are feasible and many at low/no net cost.
Additional actions that magnify benefits:
Use of bio-LNG/e-methane (when available) can deliver far deeper lifecycle reductions (bio-LNG projects claim up to ~80% cut vs HFO in best cases).
Port incentives and carbon pricing to reward verified lower-GHG bunkers.
Mandates for methane measurement and reporting across the LNG value chain to stop “invisible” leakage.
Mandate low-slip engine standards for newbuilds (limit slip, and require catalytic oxidisers where needed). (Technical studies and engine tests show big variation — standardisation matters.)
Require verified methane intensity reporting for LNG bunkers (measure, report, third-party verification). IEA modelling shows supply cuts of >60% are achievable if implemented.
Scale bio-LNG and e-methane pilot projects in major bunkering hubs to provide near-term low-carbon drop-ins. SEA-LNG and tech suppliers report early commercial availability and projects underway.
Link port/market incentives to verified lifecycle GHG (not fuel name), avoiding lock-in to any fuel that isn’t demonstrably low-GHG. ICCT and other analysts warn that unconditioned LNG uptake can derail near-term climate gains.
Accelerate research & retrofits for existing fleet (methane abatement kits, improved fuel systems), since many LNG vessels will be active for decades.
LNG offers clear air-pollution benefits today and potential climate benefits — but those climate benefits are conditional. Without strict methane control (both onboard and upstream) the near-term climate impact may be neutral or even negative (especially using short-term GWP₍20₎).
If regulators, ports and industry push the three pillars — low-slip engines, verified low-methane supply, and accelerated availability of bio/e-methane — LNG can play a meaningful bridging role while zero-carbon fuels (green ammonia, hydrogen, e-fuels) scale up. The fleet and bunker infrastructure are expanding quickly, but the climate outcome will be decided upstream and in engine rooms, not by the fuel label alone.