Half of global methane emissions come from aquatic ecosystems

A new study from the Yale School of the Environment has revealed that marine ecosystems release more methane when they are altered by human activities. The researchers found that aquatic ecosystems are the source of half of global methane emissions.

In the atmosphere, methane is a powerful greenhouse gas that is capable of trapping much more heat than carbon dioxide. It is estimated that methane is responsible for 25 percent of all warming to date.   

The global contribution and importance of aquatic ecosystems as methane emitters has been underestimated, said study lead author Judith Rosentreter.

The experts reviewed methane fluxes from 15 major natural, man-made, and human-impacted aquatic ecosystems and wetlands. The analysis showed that the cumulative methane emissions from these aquatic ecosystems are potentially a larger source of methane than direct anthropogenic methane sources, such as farming and burning fossil fuels. 

According to the study, aquatic ecosystems and wetlands contribute at least half of the total methane emissions budget.

“An accurate accounting of the sources of methane from aquatic ecosystems, and if they are impacted by human activities, is important to understanding atmospheric methane concentrations,” said study co-author Professor Peter Raymond.

One particular issue that stood out to the researchers is how humans have impacted methane emissions from aquatic sources. “Anything human-driven or human-impacted had much higher fluxes than more natural sites,” said Rosentreter.

For example, coastal aquaculture farms have methane fluxes per area that are up to 430 times higher than non-converted coastal habitats, such as mangrove forests, salt marshes, or seagrasses.

The study authors noted that there are opportunities to reduce human-induced emissions with the right management techniques.

“The intense methane emissions from aquatic ecosystems offers opportunities for intervention providing potential quick wins in reducing greenhouse emissions, provided the much large role per molecule emitted of methane compared to carbon dioxide,” said study co-author Professor Carlos M. Duarte.

A new understanding of the amount of methane emissions coming from aquatic ecosystems will help inform new monitoring strategies.

“Reducing methane emissions from aquatic systems will be an important part of stabilizing the Earth’s temperature,” said study co-author Bradley Eyre.

The study is published in the journal Nature Geoscience.

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By Chrissy Sexton, Earth.com Staff Writer