EESA climate experts are exploring how wetland emissions of methane, a potent greenhouse gas, are evolving with climate change. Their new research, published today in the journal Nature Communications, examines the degree to which intra- and inter- seasonal changes in air and soil temperatures influence the amount of methane (CH₄) released into the atmosphere by wetlands, the largest natural source of methane emissions worldwide.

Although they did find some empirical relationships between methane emissions and temperature across nearly 50 sites worldwide, the scientists concluded that it will be necessary to disentangle factors controlling those empirical relationships in order to help climate scientists reliably predict how changes in temperature might affect future methane emissions and assess how changes in temperature are impacting the methane emitted by wetlands right now. The relevant factors include things like microbial activity, thermal and hydrological dynamics, and vegetation traits.

EESA postdoc fellow Kuang-Yu Chang led the team of researchers from 46 institutions around the world to analyze methane-temperature relationships measured across 48 global wetland and rice paddy sites to unravel factors controlling methane emissions to the atmosphere.

“We know that it’s important to discover better ways to quantify global methane emissions because of methane’s shorter lifespan in the atmosphere and how much more potent it is than carbon dioxide. But the reality is that it’s much more difficult to estimate global methane emissions than global carbon dioxide emissions,” Chang said.

In 2020, EESA scientists contributed to a groundbreaking report led by the Global Carbon Project which showed that the difference in global methane emissions between the early and late 2000s was equivalent to 189 million more cars on the world’s roads in the latter part of the decade. This new study led by EESA researchers tried to address a key question that is essential to helping slow down those emissions to curb climate change.

While it doesn’t linger as long, methane traps much more heat in the atmosphere than carbon dioxide on a molecule by molecule basis. In terms of global warming potential, methane is estimated to be 84 and 28 times stronger than that of carbon dioxide over 20 and 100 year periods, respectively.

“So if you reduce the amount of methane emissions put into the atmosphere now, the upside is way bigger than if you took the same amount of carbon dioxide emissions out because methane has so much greater a warming effect,” Chang said.

“This fact creates a real opportunity to rapidly mitigate climate change by reducing or regulating methane emissions. As the atmosphere continues to warm, determining the extent to which factors, temperature in particular, increase methane emissions from natural methane sources is critical to finding ways to help reduce these emissions.”

Using global ecosystem-scale observations archived in the FLUXNET-CH₄ database, the researchers applied machine learning methods to analyze relationships between methane emissions and temperature and tried to quantify these connections.

“We asked the question ‘What are the most important factors to include in the next-generation methane models that we use to predict global methane emissions over the next decades?’” said Chang.

Senior Scientist Bill Riley, another EESA contributor to the paper, added, “The Berkeley Lab group developed the wetland model in the current version of DOE’s Earth System Model (E3SM), so these analyses will directly contribute to our ongoing work at site to regional to global scales.”

The researchers concluded that it will be necessary to incorporate microbial dynamics into next-generation methane models as these processes are important and overlooked ecosystem features that could help improve predictions of the relationships between temperature and methane emissions at sites worldwide.