Swamps, Dumps, and Cows Are Behind Rising Methane Emissions
Cows, not coal, are responsible for a big jump in methane emissions, according to new research.
The study found that leaks from oil, gas, and coal development and use have been emitting as much as 60 percent more planet-warming methane than previously thought, accounting for 20 to 25 percent of total global emissions.
But methane from agriculture production and wetlands, not fossil fuels, drove a 28-million-ton rise in atmospheric methane since 2007—to about 623 million tons a year—the researchers wrote in a study published Wednesday in the journal Nature.
Wetlands are the dominant natural source of this “biogenic” methane, while human-caused sources are mainly rice production, livestock—flatulent cows, largely—and landfills, said study lead author Stefan Schwietzke, a research scientist with the National Oceanic and Atmospheric Administration and the University of Colorado Boulder.
Methane is second to carbon dioxide as a leading driver of climate change. Although methane breaks down more quickly in the atmosphere than CO2, it is around 30 times more effective at trapping heat, making an accurate assessment of the amount and causes of methane emissions crucial to forecasting and blunting the worst impacts of global warming.
“Whether it is more wetlands or whether it is more cows and agricultural rise, we’re not sure yet,” Schwietzke said. “There are other studies that hint that it’s more likely tropical wetlands sources,” he added, where microbial activity may be increasing as a result of rising global temperatures because of climate change. “We can’t confirm this, but this is certainly a hypothesis.”
The researchers determined that fossil fuels emit 132 million to 165 million tons of methane annually—20 to 60 percent more than previously estimated. Thanks to better control of leaks in natural gas production, though, the oil and gas industry’s emissions dropped from 8 percent to 2 percent of production over the past 30 years. “But because the production of natural gas has increased so dramatically over that time, these efficiency gains have been counterbalanced,” Schwietzke said, and the industry’s total tonnage of emissions has remained roughly the same for the past three decades.
Fixing leaky energy infrastructure could be the best short-term solution for reducing methane, the researchers concluded, while more data from tropical wetlands are needed to better determine how much methane they may be producing.
To source current methane emissions, Schwietzke and his team compiled data from past research on methane concentrations in the atmosphere. Because fossil fuels create a different isotope of methane from microbial sources, the researchers were able to separate the two, creating a database with more than 10,000 data points, “the most comprehensive methane isotopic data set that has ever been compiled,” Schwietzke said. “Previous studies tried similar scientific methods, but these studies lacked the number and comprehensiveness of measurements.”
As methane also seeps naturally from fossil fuel deposits, the researchers compared contemporary levels of that isotope with preindustrial levels, which have been measured using air bubbles found in ice cores.
“Many scientists have done the measurements that we compiled, over multiple decades,” said Schwietzke. “We are standing on the shoulders of giants in being able to compile that—it is part of the scientific process.”