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A more thorough way to estimate how much the world's boreal-Arctic wetlands and lakes contribute to current and future harmful methane emissions has been developed in part by University of Alberta researchers.

The research, in Nature Climate Change, uses a novel approach to estimate future methane emissions, by taking into account both the direct effects of warming, such as longer summers and increased microbial activity, and the effects of permafrost thaw, which is creating new, often high-emission wetlands and lakes following landscape collapse.

The study is also one of the first to consider emissions from both wetlands and lakes in a unified framework, which avoids errors that occur when they are modeled separately.

The comprehensive new method represents a vital step forward in the ability to model and better understand how such emissions could increase in a warming climate, says scientist McKenzie Kuhn, who led the study to earn a Ph.D. in Land and Water Resource Management from the Faculty of Agricultural, Life & Environmental Sciences (ALES).

"It's an important tool that will help us more accurately determine emissions reductions goals; while there is no way to stop natural methane emissions, understanding their magnitude and response helps better inform how much we should reduce human sources of methane emissions to curb climate warming."

To create their improved modeling approach, Kuhn, co-author David Olefeldt, a professor in ALES, and an international research team compiled data from 189 prior studies, representing decades of field research, on methane emissions from wetlands and lakes.

The studies dated back to the 1970s, representing a total of 1,800 sites from around the world. The massive amount of information on methane emissions was then merged with the Boreal–Arctic Wetland and Lake Dataset, a map developed a few years ago by Kuhn, Olefeldt and other researchers to model such emissions.

The new method distinguishes several wetland and lake classes and accounts for their different methane emissions, addressing a "key shortcoming" of past approaches, where the assumption was that all wetlands have the same emissions, says Olefeldt.

"Merging the two datasets was crucial, as different types of wetlands and lakes have very distinct methane emissions."

For example, drier types of wetlands can have very low methane emissions, while others with thawed soils have much higher emissions. Similarly, some lake types, such as those on the Canadian shield, generally have very low emissions, while smaller ponds in peatland or tundra areas with rapid thaw have much higher emissions.

"Our study shows that a better representation of distinct wetland and lake classes greatly improves our ability to model boreal-Arctic methane emissions."

The researchers found that the net annual circumpolar methane emission from 1988 to 2019 was 20 to 40% lower than previous estimates, because their new approach more accurately characterized different types of wetland and lake ecosystems, including lower-emitting environments, such as permafrost bogs, regular bogs and glacial lakes.

These estimates are important when comparing with previous projections, which have yielded generally higher emissions, and when looking at the global methane budget. The study found that current boreal-Arctic methane emissions amount to 26 million tonnes per year, or about 15%, of the global methane emissions from wetlands and lakes.

"This helps us more accurately attribute methane in the atmosphere to appropriate sources and helps us better understand their role in the global methane budget," Kuhn says.

The more targeted approach also allowed the researchers, for the first time, to take into account scenarios where permafrost thaw causes transitions from one type of wetland or lake to another, and compare that to the direct effect of climate warming.

The study projects that under a moderate warming scenario, these methane emissions could increase by about 31% by the year 2100, primarily driven by rising temperatures, rather than the thawing of permafrost.

As a result, the research highlights that methane emissions from the boreal-Arctic region are especially sensitive to climate change, given the combined effects of warming and thaw.

"This means that climate warming could significantly enhance methane emissions from the region and could be a bigger source of global methane emissions in the future," Kuhn notes.

Closer to home, Canada has a large proportion of the world's boreal-Arctic wetlands, including two major peatland regions, the Hudson Bay Lowlands, and the Mackenzie River Basin, so the study provides valuable insight into how methane emissions from these areas will change due to climate warming and permafrost thaw, Olefeldt says.

"That information is crucial when setting global and national targets for greenhouse gas emissions, since there's a risk of overshooting climate targets if you don't account for rising methane emissions from wetlands and lakes.

"If that were to happen, Canada would need to reduce human emissions of greenhouse gases even more than our current national goals, if we are to avoid warming above the 1.5 C goal set in the Paris Agreement," he notes.