Ships Unleash Hidden Methane Emissions in Shallow Waters

A groundbreaking study from Chalmers University of Technology has revealed a startling environmental impact of ships that goes beyond fuel consumption. Researchers found that the movement of vessels through shallow waters significantly stirs up methane emissions, a potent greenhouse gas. In busy shipping lanes, methane emissions were found to be twenty times higher than in nearby undisturbed waters, suggesting that global methane estimates may have been underestimated for years.

Methane Emissions Triggered by Ship Movement

Amanda Nylund, a researcher at Chalmers University of Technology and the Swedish Meteorological and Hydrological Institute (SMHI), explained the mechanism behind these emissions. According to Nylund, “Our measurements show that ship passages trigger clear pulses of high methane fluxes from the water to the atmosphere.” This phenomenon occurs due to pressure changes and the mixing of water masses caused by ships passing through. Although these methane pulses are brief, their cumulative effect throughout the day is significant.

This revelation shifts the focus of emissions concerns from ships powered by liquefied natural gas (LNG) to the methane released from the seafloor itself, disturbed by ship traffic. This means that all types of vessels, regardless of their fuel source, contribute to methane emissions. The study highlights the need to reassess how emissions from maritime activities are monitored and reported.

Shallow Marine Environments: A Methane Hotspot

The research concentrated on shallow marine areas rich in organic matter, where oxygen-free sediments create ideal conditions for methane production. In these environments, methane accumulates naturally within the seafloor and typically escapes slowly in small bubbles. However, the passage of a ship alters this dynamic. The sudden pressure changes triggered by a vessel can cause large amounts of methane to be released from the sediments.

The mixing action created by a ship’s wake further accelerates the release of methane, allowing it to rise quickly to the surface and escape into the atmosphere. As ships frequently traverse these waters, the resulting methane emissions can accumulate to alarming levels.

The researchers initially discovered this phenomenon while conducting unrelated measurements in Neva Bay, part of the Baltic Sea. Their unexpected findings have now been published in *Nature Communications Earth & Environment*. Johan Mellqvist, a professor of Optical Remote Sensing at Chalmers, emphasized the importance of this discovery for improving global methane emission estimates, particularly given that many of the world’s largest ports are located in similar shallow waters.

Implications for Global Methane Emission Estimates

The study also examined emissions from various types of ships. Surprisingly, large cruise ships and container vessels produced the highest methane emissions, while smaller ropax vessels, which carry both passengers and cargo, also exhibited significant release rates. Conversely, larger bulk carriers showed lower emissions than anticipated, challenging the assumption that bigger ships always result in greater emissions.

The researchers suggest that ship design may play a role in these findings. Rickard Bensow, a professor of Hydrodynamics at Chalmers, noted that the double propellers on ropax vessels could contribute to their higher emissions.

Given the study’s findings, researchers are calling for urgent changes in how methane emissions from ships are monitored. They plan to expand their investigation to include major ports in river deltas, where similar methane risks may exist. Professor Ida-Maja Hassellöv, who will lead the follow-up project, stated, “It is very likely that we underestimate methane emissions in major ports around the world.”

This research could lead to significant changes in global climate strategies and shipping regulations, highlighting the need for stronger controls on ship routes and operations in sensitive coastal areas. The study underscores the hidden climate risks associated with maritime activities, revealing that ships do more than transport goods—they may also be contributing to greenhouse gas emissions with every wave they create.