Stockholms Universitet : Challenges in adding up the sources of methane

The greenhouse gas methane has many natural sources, and understanding how large each of those sources are remains an unfinished task. This is important when trying to predict future methane emissions and global warming. A new study from researchers at Stockholm University shows how double-counting of methane sources, particularly wetlands and lakes, might be occurring in research. The study has been published in Geophysical Research Letters.

Wetland edges at Stordalen Mire, near Abisko in northern Sweden. Photo: Brett Thornton.

'When we calculate how much methane is emitted, now or in the future, we have two ways to do that - either we look at how much is in the atmosphere and calculate backwards to the sources, or we add up all the sources. A problem is that those two methods can give us very different results', says Brett Thornton at the Department of Geological Sciences and Bolin Centre for Climate Research, Stockholm University, who led the study.

'The difficulty is that if you have one group of researchers studying methane emissions from lakes, and one group studying wetlands- what happens if the definitions of wetlands include very shallow lakes? Then we may be counting methane emissions twice', says Martin Wik, also at the Department of Geological Sciences and Bolin Centre for Climate Research, Stockholm University.

One of the common tools geoscientists use for identifying methane sources are isotopes (different varieties of carbon and hydrogen atoms) which are more or less abundant in a sample of methane depending on where and how that methane was produced. But the tool isn't perfect: in the Arctic, many sources produce methane with similar isotopic signatures.

'We can do better, but only if we develop better ways to distinguish Arctic methane sources, and have the models to better represent the measurements,' says Patrick Crill, Professor at the Department of Geological Sciences, Stockholm University.

About methane

Although the growth in global carbon dioxide concentrations has been slowing, methane emissions are now rising faster than at any time during the past two decades. Methane is about 30 times better at trapping heat than carbon dioxide on timescales of a century. Methane emissions to the atmosphere are expected to increase if the Earth's climate warms, particularly in sub-Arctic and Arctic regions.

About the study

The study was a collaboration between Brett Thornton, Martin Wik, and Patrick Crill who are part of the Trace Gas Biogeochemistry group at the Department of Geological Sciences, Stockholm University, a laboratory that has been involved in methane measurements for the past 15 years.

Link to the study.

Brett Thornton and Patrick Crill also recently participated in a major international project, which aimed to improve the understanding of variations and recent changes in atmospheric methane across the globe.