More methane will be released into the atmosphere as northern wetland areas thaw and more tropical wetlands warm up, according to new research that links atmospheric methane with wetland emissions.

Writing in the journal Global Change Biology, lead study author Merritt Turetsky, an integrative biology professor at University of Guelph, reports the results of one of the largest global methane-emissions analyses to date.

Methane is released into the atmosphere from a variety of sources, including agriculture and fossil fuel use, as well as natural avenues such as microbes in saturated wetland soils.

Atmospheric methane emissions had remained relatively stable for nearly a decade, but in 2007 levels were documented on the rise, and researchers began looking for reasons why.

Previous research had indicated that the largest release of wetland methane occurred in tropical climates, but Turetsky and his colleagues' research comes to a different conclusion.

"[Our] analyses show that northern fens, such as those created when permafrost thaws, can have emissions comparable to warm sites in the tropics, despite their cold temperatures. That's very important when it comes to scaling methane release at a global scale," he said in a news release.

Common northern ferns in Canada are one of the region's strongest sources of greenhouse gasses, Turetsky said, noting that as tundra covering high-latitude forests undergoes melting, it creates an ecosystem that produces a lot of methane.

Small temperature changes, such as those associated with thawing, can release more methane into the atmosphere, the researchers learned. However, soil moisture is also key in determining how much methane is emitted from soil microbes. More gas is emitted under warmer, wetter conditions.

The researchers considered nearly 20,000 field data measurements collected from 70 sites across arctic, temperate and tropical regions. 

Study co-author Narasinha Shurpali, from University of Eastern Finland, said that most methane studies just take a single site into account.

"Our synthesis of data from a large number of observation points across the globe is unique and serves an important need," Shurpali said.