The world’s warming tropical wetlands are releasing more methane than ever before, research shows — an alarming sign that the world’s climate goals are slipping further out of reach.
A massive surge in wetlands methane — unaccounted for by national emissions plans and undercounted in scientific models — could raise the pressure on governments to make deeper cuts from their fossil fuel and agriculture industries, according to researchers.
Wetlands hold huge stores of carbon in the form of dead plant matter that is slowly broken down by soil microbes. Rising temperatures are like hitting the accelerator on that process, speeding up the biological interactions that produce methane. Heavy rains, meanwhile, trigger flooding that causes wetlands to expand.
Scientists had long projected wetland methane emissions would rise as the climate warmed, but from 2020 to 2022, air samples showed the highest methane concentrations in the atmosphere since reliable measurements began in the 1980s.
Four studies published in recent months say that tropical wetlands are the likeliest culprit for the spike, with tropical regions contributing more than 7 million tonnes to the methane surge over the last few years.
“Methane concentrations are not just rising, but rising faster in the last five years than any time in the instrument record,” said Stanford University environmental scientist Rob Jackson, who chairs the group that publishes the five-year Global Methane Budget, last released in September.
Satellite instruments revealed the tropics as the source of a large increase. Scientists further analyzed distinct chemical signatures in the methane to determine whether it came from fossil fuels or a natural source — in this case, wetlands.
The Congo, Southeast Asia and the Amazon and southern Brazil contributed the most to the spike in the tropics, researchers found.
Data published in March 2023 in Nature Climate Change shows that annual wetland emissions over the past two decades were about 500,000 tonnes per year higher than what scientists had projected under worst-case climate scenarios.
Capturing emissions from wetlands is challenging with current technologies.
“We should probably be a bit more worried than we are,” said climate scientist Drew Shindell at Duke University.
The La Nina climate pattern that delivers heavier rains to parts of the tropics appeared somewhat to blame for the surge, according to one study published in September in the journal Proceedings of the National Academy of Sciences.
But La Nina alone, which last ended in 2023, cannot explain record-high emissions, Shindell said.
For countries trying to tackle climate change, “this has major implications when planning for methane and carbon dioxide emissions cuts,” said Zhen Qu, an atmospheric chemist at North Carolina State University who led the study on La Nina impacts.
If wetland methane emissions continue to rise, scientists say governments will need to take stronger action to hold warming at 1.5 C (2.7 F), as agreed in the United Nations Paris climate accord.
WATER WORLD
Methane is 80 times more powerful than carbon dioxide (CO2) at trapping heat over a timespan of 20 years, and accounts for about one-third of the 1.3 degrees Celsius (2.3 F) in warming that the world has registered since 1850. Unlike CO2, however, methane washes out of the atmosphere after about a decade, so it has less of a long-term impact.
More than 150 countries have pledged to deliver 30% cuts from 2020 levels by 2030, tackling leaky oil and gas infrastructure.
But scientists have not yet observed a slowdown, even as technologies to detect methane leaks have improved. Methane emissions from fossil fuels have remained around a record high of 120 million tonnes since 2019, according to the International Energy Agency’s 2024 Global Methane Tracker report.
Satellites have also picked up more than 1,000 large methane plumes from oil and gas operations over the past two years, according to a U.N. Environment Programme report published on Friday, but the countries notified responded to just 12 leaks.
Some countries have announced ambitious plans for cutting methane.
China last year said it would strive to curb flaring, or burning off emissions at oil and gas wells.
President Joe Biden’s administration finalized a methane fee for big oil and gas producers last week, but it is likely to be scrapped by the incoming presidency of Donald Trump.
The Democratic Republic of Congo’s environment minister Eve Bazaiba told Reuters on the sidelines of the U.N. climate summit COP29 that the country was working to assess the methane surging from the Congo Basin’s swampy forests and wetlands. Congo was the largest hotspot of methane emissions in the tropics in the 2024 methane budget report.
“We don’t know how much [methane is coming off our wetlands],” she said. “That’s why we bring in those who can invest in this way, also to do the monitoring to do the inventory, how much we have, how we can also exploit them.”