Higher temperatures increase methane emissions from freshwater environments

Rising global temperatures will lead to increasing natural emissions of greenhouse gas methane from freshwater environments – something that, in turn, could contribute to further warming of the Earth, as shown in a study now being published in Nature.

The study is based on data from hundreds of experiments and field measurements, and shows that methane emissions from wetlands, lakes, and rice fields is increasing with the increasing temperatures, in the same way as in laboratory experiments where methane formation in sediment was studied.

“This is very important information for understanding how nature and the natural emissions of greenhouse gases react to climate change,” says David Bastviken of Water and Environmental Studies at Linköping University, one of the initiators of the study.

“Even if we knew that increasing temperatures favour the micro-organisms that produce methane, we did not previously know whether this would lead to greater emissions into the atmosphere. But, unfortunately, that now seems to be the case.”

Our freshwater environments, including those created by people (e.g. dams and rice paddies) are already contributing more than half of the global methane emissions into the atmosphere; the results of the study mean that future greenhouse gas emissions from these environments has been underestimated.

“We hope that our study will contribute knowledge of how we should go further to better take the natural methane emissions in the climate models into consideration,” Mr Bastviken says.

Methane is one of the most important greenhouse gases; over 100 years, 1 kilogramme of methane yields 25 times the warming effect of 1 kilogramme of carbon dioxide in the atmosphere. Methane is produced primarily by a group of ancient micro-organisms called Archaea, and methane formation occurs during the breakdown of organic material in oxygen-free environments.

The article, which will be published in Wednesday’s issue of the leading scientific journal Nature, shows that carbon dioxide emissions from freshwater environments also increase if it gets warmer, but that methane emissions increase even more quickly. This means that the significance of methane for the climate could gradually increase compared with carbon dioxide in a warmer future.

The article is titled “Methane fluxes show consistent temperature dependence across microbial to ecosystem scales”. Its authors are Gabriel Yvon-Durocher, Andrew P. Allen, David Bastviken, Ralf Conrad, Cristian Gudasz, Annick St-Pierre, Nguyen Thanh-Duc and Paul A. del Giorgio.