Methane Emissions in Shipping Higher Than We Thought, Study Finds

• Ship movements in shallow, organic-rich waters can release methane emissions up to 20 times higher than in undisturbed areas.
• Methane fluxes are linked to ship-induced pressure changes and water mixing, not just LNG fuel usage.
• Researchers urge a reassessment of global methane estimates, particularly near major ports and coastal zones.

A recent study led by Chalmers University of Technology has uncovered a significant but previously overlooked source of methane emissions: the movement of ships through shallow waters. Researchers recorded methane levels up to 20 times higher in busy shipping lanes compared to nearby undisturbed areas. These findings highlight a hidden environmental cost of maritime transport that goes beyond traditional exhaust emissions, according to Innovation News Network.

Methane Pulses Triggered by Passing Vessels

According to Amanda Nylund, a researcher at Chalmers and the Swedish Meteorological and Hydrological Institute (SMHI), the passage of ships through shallow marine environments creates sudden pulses of methane being released from the seabed into the atmosphere. These emissions, though brief, accumulate throughout the day to significant levels. The pressure changes on the seafloor, combined with water turbulence created in the ships’ wake, facilitate the escape of methane bubbles from oxygen-deprived sediments rich in organic matter.

Fuel Type Not the Primary Factor

Although methane emissions from LNG-powered vessels have drawn scrutiny, the study reveals that these emissions are largely independent of the type of fuel used. In fact, even vessels not running on LNG were found to release considerable methane. The root cause lies not in combustion, but in how ship activity disturbs methane-rich sediments in shallow water regions. The findings suggest that the broader shipping industry’s contribution to greenhouse gas emissions may be underestimated.

Certain Vessel Types More Emission-Intensive

The research also identified patterns in methane emissions based on vessel type. Cruise and container ships were responsible for the most frequent and intense methane discharges. However, ropax vessels—which carry both cargo and passengers—also produced substantial emissions, likely due to their dual-propeller systems. In contrast, bulk carriers, despite their larger size, were associated with relatively lower emissions, indicating that vessel design and operational behavior may be more influential than size alone.

Implications for Global Methane Monitoring

This phenomenon was first discovered during unrelated measurements in Neva Bay, part of the Baltic Sea, and has prompted scientists to call for a reevaluation of where and how methane emissions are tracked. Professor Johan Mellqvist, who led the optical remote sensing work, noted that many of the world’s largest ports—located in similarly shallow, organic-rich waters—may also be hotspots for unaccounted methane emissions.

Call to Expand Global Methane Emission Assessments

With follow-up research already planned, scientists aim to quantify the broader implications of these findings. Ports in regions like China, Singapore, South Korea, Germany, and Europe’s North Sea coast are now under particular scrutiny. Professor Ida-Maja Hassellöv, who will lead the next phase of the study, emphasized the importance of including these areas in global greenhouse gas inventories, warning that current estimates may significantly underreport methane emissions from shipping activities in such environments.

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