Assessing the climate footprint of LNG as a marine fuel: evidence from a high-resolution AIS-based emission model for Spain

LNG adoption in shipping is often presented as a route to lower air-pollutant emissions and meet tighter sulphur limits under IMO 2020 and EU in-port requirements. The climate side is trickier: LNG-related methane (CH₄) emissions depend heavily on CH₄ slip, and that matters more under new EU policies that price and regulate greenhouse gases (GHG) emissions. Since January 2025, the FuelEU Maritime applies well-to-wake GHG-intensity targets, while from January 2026, CH₄ emissions from maritime transport also fall under the EU Emissions Trading System.

Here we present results on shipping CH₄ emissions over Spain derived from a near-real-time, high-resolution Automatic Identification System (AIS)-based emission model developed within the RESPIRE-CLIMATE national project, which received formal endorsement from the WMO-IG3IS initiative. Using 2019–2025 AIS trajectories, we quantify CH₄ slip from LNG-fuelled ships using engine-type- and load-dependent emission factors. The system is fully operational and generates daily outputs per ship type on a 0.01°×0.01° grid.

Across Spanish waters, we detect a marked increase in LNG-related activity after 2022, consistent with Europe’s rapid shift in gas supply chains following the war in Ukraine. Spain is indeed a major LNG gateway in Europe, with roughly one-third of Europe’s regasification capacity, which supports high LNG carrier traffic and enables re-export flows.

A Barcelona case study shows how this trend intersects with intensified LNG operations, reaching 618 port calls of LNG-fuelled ships during 2023. Results highlight where and when CH₄ slips concentrate near ports and in traffic lanes and which ship types are driving the largest emission peaks. They also show how, for several major cruise and cargo ships, CH₄ slip can substantially change the CO₂-equivalent balance of LNG-fuelled ships under certain operating profiles.

The results presented in this study can contribute to the monitoring, reporting, and verification activities of GHG emissions from the maritime transport.