New study sheds light on how much methane is produced by Arctic lakes and wetlands

When it comes to greenhouse gases, methane is one of the biggest contributors. Not only is it massively abundant, but it is about 25 times more powerful than carbon dioxide at trapping heat in the atmosphere.

This makes monitoring methane emissions crucially important, and particularly in the Arctic, which is now the fastest warming region on the globe.

A new study from Brown University helps shed light on actual atmospheric methane emissions from Arctic lakes and wetlands, which are important producers of the gas but remain largely unmapped. The results were published in Geophysical research letters.

Using NASA’s unprecedented high-resolution satellite and airborne imagery – harnessing the technology to overcome obstacles posed by the size of the region and the many natural land formations that are major producers of methane – two researchers have produced new estimates and found that these unmapped lakes are not the large methane emitters that previous research has made them out to be.

Instead of contributing about 40 percent of the region’s methane emissions, small, unmapped lakes contribute only about 3 percent, according to the study.

“What the research has shown is that these smaller lakes are the largest emitters of methane by area, meaning that even though they occupy a small part of the landscape, they have a disproportionate level of emissions” , said Ethan D. Kyzivat, who led the study as part of his Ph.D. at Brown.

“Traditionally, we don’t have a good idea of ​​how much land they occupy, but this new high-resolution data set has helped us expand that to ultimately make these estimates much more accurately.”

These new results contradict nearly 15 years of research based on older datasets with much lower resolution quality. In older data, the number of visible small lakes was statistically extrapolated to produce estimates for the region of the total number of unmapped small lakes and the amount of methane they emitted.

The new analysis of aerial imagery showed researchers, including Brown Professor Laurence C. Smith, that there are far fewer small, unmapped lakes than previously estimated, significantly reducing the cumulative amount of methane they were supposed to emit.

The study focuses on small lakes with an area of ​​about a tenth of a square kilometer or less, which is equivalent to about 20 football fields. Kyzivat, who is now a postdoctoral researcher at Harvard University, spent more than two years working on the study, initially compiling the data while working on his master’s degree, then analyzing and writing the paper while preparing his Ph.D. at Brown.

The project began as an effort to search for hidden lakes in the Arctic, but evolved as researchers examined the data more closely. The effort, which involved combining high-resolution airborne data with a global map of Arctic region lakes, also uncovered some unexpected but welcome results.

The work shows, for example, that many small and large lakes are still counted twice as wetlands. This double-counting inflates methane emissions estimates for the region, but with new discoveries of fewer small, unmapped lakes, researchers believe the problem is smaller than previously thought. thought before.

Another unexpected result comes from the methodology.

In the field of methane modeling, there are two widely held schools of thought. The first consists of “bottom-up” estimates, which model methane emissions based on maps of the Earth, as the researchers do here. The other method is “top-down” estimates, which model methane based on atmospheric measurements. According to Smith, for more than a decade there has been a troubling discrepancy between the numbers produced by these two methods.

The new figures from the analysis could help reconcile the two opposing views by bridging the difference between them.

“It’s probably been 15 to 20 years of disagreement, but the bottom line is that the satellite resolution is now there so the ‘bottom-up’ community can get a better look at how much methane is actually being emitted.” , said Smith, who is a professor of environmental studies and earth, environmental and planetary sciences.

“We can now see the smallest of these water masses and they are not as abundant as we extrapolate. The end result of all this is going to reduce the bottom-up estimates to make them more in line with predictions.” top-down estimates. This will unify these two communities.

For this reason, Kyzivat and Smith consider the study’s work a proof of concept and are now looking to expand their methane modeling technique to other parts of the world.

“The next step is to go global,” Kyzivat said.