Ships Trigger Hidden Methane Emissions from Seabed todayheadline

Ship traffic in shallow coastal waters generates massive methane emissions simply by moving through the water—a previously unrecognized source of greenhouse gas pollution that could affect global climate calculations.

Swedish researchers discovered that ship passages trigger methane releases twenty times higher than nearby undisturbed areas, with emissions caused by pressure changes and water mixing rather than ship fuel choice.

The findings suggest that all ships, regardless of fuel type, contribute to methane emissions through their physical presence in methane-rich waters. This challenges current understanding of shipping’s climate impact and reveals gaps in greenhouse gas accounting methods.

The Pressure Connection

Researchers from Chalmers University of Technology observed clear pulses of methane escaping from water to atmosphere as ships passed through shallow areas. The mechanism works like this: when ships move through water, they create pressure changes on the seafloor that force methane bubbles out of sediments more easily.

“Our measurements show that ship passages trigger clear pulses of high methane fluxes from the water to the atmosphere. This is caused by pressure changes and mixing of the water mass,” explained Amanda Nylund, researcher at Chalmers University of Technology and the Swedish Meteorological and Hydrological Institute.

The study measured pressure changes of 30-60 mbar beneath ships—similar to pressure variations known to trigger methane release in other marine environments. Combined with turbulent mixing in ship wakes, these pressure drops create perfect conditions for methane escape.

Surprising Scale of Emissions

The research team studied ship traffic in Russia’s Neva Bay and found remarkable emission levels:

• Daily methane emissions reached 120 kg from just 5.5 kilometers of shipping lane
• Methane flux was 11 times higher than typical coastal areas globally
• Container and cruise ships triggered the most frequent large emissions
• Even smaller ferry vessels generated substantial methane releases

All Ships Are Culprits

Unlike methane slip from liquefied natural gas engines—a known issue affecting only certain vessels—these emissions occur regardless of fuel type. Any ship moving through methane-rich sediment areas can trigger releases, making this a universal shipping impact.

The study revealed that ship size, speed, and design all influence emission magnitude. Ships longer than 250 meters always triggered emissions, while vessels under 125 meters rarely did. Speed mattered too—ships traveling faster than 12 knots generated the largest methane pulses.

Interestingly, the research uncovered technical details not emphasized in initial reports: twin-propeller vessels like passenger ferries created particularly large emissions, possibly because dual propellers affect larger water volumes and enhance gas exchange efficiency.

Climate Implications

Methane packs 27 times more warming potential than carbon dioxide over a century, making these emissions climatically significant. The researchers calculated that ship-triggered methane represented 22% additional warming compared to the ships’ fuel combustion emissions.

“Even if the pulses are short, the total amount during a day is significant,” Nylund noted. The phenomenon was discovered accidentally during other measurements, highlighting how easily such emissions can be overlooked.

The timing couldn’t be more relevant. As shipping works toward net-zero emissions by 2050, these newly identified methane sources will represent an increasing percentage of total shipping climate impact—particularly since they’re not addressed by current emission reduction strategies.

Global Hotspots

The discovery has worldwide implications because nine of the world’s ten largest ports sit in waters with similar conditions to Neva Bay. Major ports in China, Singapore, South Korea, and European hubs like Rotterdam and Antwerp likely experience comparable methane emissions.

“The next step is to estimate how large these effects can be globally,” said Ida-Maja Hassellöv, Professor of Maritime Environmental Science at Chalmers, who will lead follow-up research starting this autumn.

The study suggests that current methods for measuring coastal methane emissions systematically underestimate totals by avoiding shipping lanes—precisely where some of the largest emissions occur.

As global shipping traffic continues growing, understanding and potentially mitigating these hidden emissions becomes crucial for accurate climate accounting and effective environmental policy.

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