Warming May Increase Freshwater Methane Emissions

By Tim Radford, Climate News Network

LONDON – British scientists have identified yet another twist to the threat of global warming. Any further rises in temperature are likely to accelerate the release of methane from rivers, lakes, deltas, bogs, swamps, marshlands and rice paddy fields.

Swamps, marshes, rice paddies and other freshwater ecosystems are sources of methane, which increases with the rise in temperatures.
Credit: vataeparksstaff, Wikimedia Commons via Climate News Network

Methane or natural gas is a greenhouse gas. Weight for weight, it is more than 20 times more potent than carbon dioxide over a century, and researchers have repeatedly examined the contribution of natural gas emitted by ruminant cattle to global warming. But Gabriel Yvon-Durocher of the University of Exeter and colleagues considered something wider: the pattern of response to temperature in those natural ecosystems that are home to microbes that release methane.

They report in Nature that they looked at data from hundreds of field surveys and laboratory experiments to explore the speed at which the flow of methane increased with temperature.

Microbes, algae, freshwater plants and animals are all part of an active ecosystem and take their nourishment from and return waste to the atmosphere. Healthy plants take carbon dioxide from the atmosphere with photosynthesis.

Most of the methane in freshwater systems is produced by an important group of microbes called Archaea that live in waterlogged, oxygen-free sediments and play an important role in decay.

Plant uptake of carbon dioxide is affected by temperature, and so is microbial methane production. Respiration also releases carbon dioxide. The questions the researchers set out to answer were: which gas is more likely to be released in greater quantities as temperatures rise? And is the outcome the same whether they examine the Archaea only, or all the microbes in an ecosystem, or the entire package of submerged freshwater life?

More Heat, More Methane

The answer is, the scientists say, that methane emissions go up with the mercury, and that the ratio of methane to carbon dioxide also goes up in step with temperature. And the result is the same whether you consider the microbes or the whole ecosystem.

Scientists say methane emissions go up with the mercury, and the ratio of methane to CO2 also goes up in step with temperature.
Credit: Mberjano/Flickr

“The discovery that methane fluxes are much more responsive to temperature than the processes that produce and consume carbon dioxide highlights another mechanism by which the global carbon cycle may serve to accelerate rather than mitigate future climate change,” says Dr. Yvon-Durocher.

This is not the end of the story. All such studies raise as many questions as they answer, and more research is necessary. The next puzzle is how to fit such findings into models of climate change. However, the researchers feel they have cleared up one point. Dr. Yvon-Durocher says:

“Our research provides scientists with an important clue about the mechanisms that may control the response of methane emissions from ecosystems to global warming.” 

Tim Radford is a reporter for Climate News Network.Climate News Network is a news service led by four veteran British environmental reporters and broadcasters. It delivers news and commentary about climate change for free to media outlets worldwide.