BYLINE: Elise Mahon

Newswise — MADISON –– Scientists have been measuring global methane emissions for decades, but the boreal arctic —with a wide range of biomes including wetlands that extend across the northern parts of North America, Europe and Asia — is a key region where accurately estimating highly potent greenhouse gas emissions has been challenging.

Wetlands are great at storing carbon, but as global temperatures increase, they are warming up. That causes the carbon they store to be released into the atmosphere in the form of methane, which contributes to more global warming.

Now, researchers — including the University of Wisconsin–Madison’s Min Chen and Fa Li — have developed a new model that combines several data sources and uses physics-guided machine learning to more accurately understand methane emissions in the region. The improved model shows these wetlands are producing more methane over time.

“Wetland methane emissions are among the largest uncertainty in emissions from natural systems,” explains Chen, a professor of forest and wildlife ecology in the UW–Madison College of Agriculture and Life Sciences. “There are bacteria that live in the soils under the water of wetlands. That’s the perfect limited oxygen environment that is suitable for methane production.”

The researchers recently published their findings in the journal Nature Climate Change.


What problem are researchers trying to solve?

  • Currently, models used to quantify methane emissions in the boreal arctic wetlands don’t agree on how much of the gas is being emitted and whether the amount is increasing over time.
  • Previously, to help moderate emissions of carbon and methane, a collaboration of scientists created the Global Methane Budget under the Global Carbon Project, which they hope will inform policymakers.
  • However, Chen says, if scientists want to quantify the global methane budget accurately, they need to have more certainty in how much methane is emitted by these wetlands.
  • So, he and other researchers collaborated to build a more accurate and reliable model to better understand the region’s methane contribution as global temperatures rise.


Why do scientists need more information on emissions from these wetlands?

  • The boreal arctic holds up to 50% of the world’s wetlands.
  • With rising global temperatures, the region spends less time frozen over and plants and microbes are growing and productive for longer periods of time. This creates conditions for more methane emissions.


How does the new model help?

  • The team created the largest dataset yet for the region, which allowed them to develop a more accurate data-driven model of the boreal arctic wetlands’ methane emissions.
  • Chen says that previous models did not account for the full complexity of the physical and chemical processes at play, such as substrate availability, microbial activity, and other environmental conditions that influence methane emissions.
  • This is because they relied on partial emissions data collected from either a network of towers around the region or from chambers that take readings from the ground and surface of the water.
  • Though the towers are a “gold standard for measuring the flux of greenhouse gasses between land and the atmosphere,” Chen says, in the boreal arctic, they’re mostly not located close to the largest methane emitters in the region. Meanwhile, the chambers are near these hotspots.
  • Whereas prior models then only had one part of the complete picture and had to extrapolate to estimate the full picture, the new model combines data from both the tower and chamber sources.
  • The scientists also used artificial intelligence to create additional constraints that better account for how environmental variables like precipitation influence methane emissions.


What the new model is uncovering

  • Researchers are finding that methane emissions in the region have increased over time.
  • They’ve also found that higher temperatures and increased plant productivity are the biggest drivers of increased methane emissions in the region. When plants are more productive, they increase the amount of carbon in the soil, which acts as fuel for the soil-microbes that produce methane.
  • By improving scientific understanding and the ability to project greenhouse gas emissions, researcher can more accurately estimate temperature increases in the future, Chen says.
  • The team hopes to apply their model on a global scale, a task which will require wrangling a much larger data set.


            This research was supported by a NASA Carbon Monitoring System grant (NNH20ZDA001N) and the Reducing Uncertainties in Biogeochemical Interactions through Synthesis and Computation (RUBISCO) Scientific Focus Area Project; the latter is sponsored by the Earth and Environmental Systems Modeling (EESM) Program under the Office of Biological and Environmental Research of the US Department of Energy Office of Science. This work was done in collaboration with researchers from Lawrence Berkely National Laboratory, University of Illinois Chicago, Stanford University, and the University of British Columbia.