Kaleigh Harrison
A major study has uncovered an unexpected environmental side effect of global shipping: commercial vessels passing through shallow waters can trigger significant methane emissions. Researchers from Chalmers University of Technology in Sweden found that ship movements in coastal and port areas release methane at levels up to twenty times higher than in undisturbed zones — a revelation that could force a rethink in how shipping emissions are tracked and managed.
Unlike the better-known methane risks tied to liquefied natural gas (LNG) fuel systems, these emissions occur regardless of what a ship burns. The problem stems from the physical impact ships have on seabeds rich in organic sediments. As vessels move through these shallow zones, they create strong pressure changes and water mixing in their wake. This disruption allows trapped methane to escape into the atmosphere, creating short-lived but repeated pulses of emissions that, when aggregated, represent a serious climate threat.
Container ships and cruise vessels appear to be the main culprits, with their frequent movements in busy port areas driving repeated sediment disturbances. The study also found that ships using double propeller configurations — common on passenger ferries and some cargo carriers — tend to stir up more methane than single-propeller vessels, adding another layer of complexity for ship design and operational decisions.
A Global Challenge for Ports and Shipping Giants
The findings point to a global-scale challenge. While the research focused on the Baltic Sea, similar sediment conditions exist in most of the world’s major ports, from Singapore to Rotterdam. In fact, nine out of the ten busiest ports worldwide operate in shallow-water environments, suggesting this newly identified emission source is widespread.
The implications go beyond environmental compliance. Shipping companies may need to rethink route planning and operational strategies to mitigate these unintended emissions. Port authorities, too, could be pushed to incorporate seabed management and vessel movement guidelines into their climate action plans.
The Chalmers team plans to scale up their monitoring efforts, especially targeting large river delta ports and coastal hubs where methane production in sediments is highest. Future policy discussions may soon need to factor in this hidden methane source when setting emissions standards and incentives for greener shipping.