How Ship Movements are Silently Supercharging Methane Emissions

By Muhammad OsamaReviewed by Laura ThomsonMay 22 2025

In a recent article published in the journal Communications Earth & Environment, researchers comprehensively explored methane (CH₄) emissions triggered by ship passages in coastal and estuarine environments, focusing on Neva Bay, Russia. The goal was to address the often overlooked contribution of maritime activities to greenhouse gas release and highlight the need to include ship-related impacts in existing emission inventories for effective climate mitigation strategies.

Environmental Implications of Maritime Methane Release

CH₄, the second most potent greenhouse gas after carbon dioxide (CO₂), significantly impacts climate change due to its high global warming potential. Estimates indicate that 35-41% of global emissions originate from aquatic systems, particularly estuarine and shallow coastal regions. These are driven by natural processes such as ebullition and diffusion, influenced by factors like pressure changes and water mixing. External factors, including tidal shifts and human activities, can intensify these emissions.

Ships contribute to CH₄ emissions through fuel combustion and sediment disturbance. Vessel-induced turbulence and pressure variations trigger their release from the seafloor, an effect largely absent from current emission inventories. Therefore, understanding these emissions is essential for improving budget assessments and climate strategies.

Investigating Ship-Triggered Methane Emissions

In this paper, the authors quantified emissions in Neva Bay, a busy maritime zone with high levels of CH₄. They conducted two campaigns in 2011 and 2012, combining atmospheric measurements with computational models to assess the effects of vessel movements.

The researchers used high-precision Picarro cavity ring-down spectrometers (CRDS) to measure CH₄ and CO₂ concentrations in ship plumes. A total of 464 ship passages were recorded, with 220 meeting quality standards for comprehensive analysis. Observations included environmental parameters such as wind speed, water temperature, and salinity, alongside ship-specific data from the Automatic Identification System (AIS).

Computational fluid dynamics (CFD) modeling, primarily using Detached Eddy Simulation (DES), simulated hydrodynamic interactions caused by ships, focusing on pressure changes near the seabed and turbulence from ship wakes. These simulations were validated against observed concentrations to estimate emissions. Furthermore, a mixture modeling framework was applied, utilizing logistic regression to detect CH₄ emissions and log-normal regression to quantify levels, emphasizing the role of vessel size, speed, and draught.

Key Findings on Methane Emission Patterns

The outcomes showed that ship-induced CH₄ emissions in the Neva Bay shipping lane were substantially higher than reported estimates for similar environments. The authors measured an average CH₄ flux of approximately 11.1 mmol m^-2 day^-1, 10 to 1,000 times greater than global estuarine values and comparable to major aquatic CH₄ hotspots.

During a 24-hour sampling period, 79 emission plumes were detected, amounting to roughly 120 kg daily. About 28% of ship passages were linked to significant release events, particularly from large vessels like container ships and cruise liners, with some exceeding median values by more than ten times. CH₄ emissions also contributed to a 22% increase in CO₂ equivalents compared to emissions from ship fuel combustion alone.

A strong correlation between ship-induced pressure changes and CH₄ release was also observed, with a threshold of approximately 60 mbar identified as critical for triggering emissions. These pressure fluctuations and turbulence from ship wakes facilitated CH₄ release from sediments, particularly in shallow waters. Overall, the results highlight the previously overlooked role of maritime traffic in enhancing CH₄ emissions.

Practical Applications for Sustainable Maritime Practices

This research has significant implications for clean technology and environmental management. It highlights the urgency of revising current emission inventories to include shipping lanes when assessing CH₄ levels in coastal and estuarine environments. Operational changes, such as utilizing smaller and slower vessels, could help reduce emissions and underwater noise, benefiting marine ecosystems. This study provides detailed guidance for policymakers, maritime authorities, and environmental agencies, potentially leading to effective regulations for reducing greenhouse gas emissions at sea.

Conclusion and Future Directions

The study demonstrates that maritime activities play a key role in CH₄ emissions in coastal regions, a source often overlooked in climate assessments. The flux triggered by ship movements was comparable known emission hotspots, highlighting the role of including shipping lanes in future climate evaluation frameworks.

Future work should focus on direct field measurements of pressure shifts, sediment gas fluxes, and how environmental variables like salinity and temperature affect release rates.

As shipping grows globally, tracking and managing its environmental footprint will be essential. A more detailed understanding of these processes will help guide mitigation strategies and contribute to more sustainable maritime operations.

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