According to the research published online Wednesday in the journal Nature, they may be as much as 60 percent greater.
"Our study shows that leaks from oil and gas activities around the world are responsible for a lot more methane than we thought," said co-author Lori Bruhwiler, a National Oceanic and Atmospheric Administration (NOAA) research scientist, in a press statement.
Out of the 623 million tons of methane—which comes in second after CO2 for greenhouse gas potency—emitted by all sources annually, fossil fuels are responsible for 132 million to 165 million tons, or roughly 20-25 percent, the team lead by NOAA and the Cooperative Institute for Research in Environmental Sciences (CIRES) scientists found.
Using the emissions' "isotopic signatures," the researchers were able to determine if the they were from fossil fuels or other sources.
The study's abstract states: "Our findings imply a greater potential for the fossil fuel industry to mitigate anthropogenic climate forcing, but we also find that methane emissions from natural gas as a fraction of production have declined from approximately 8 percent to approximately 2 percent over the past three decades."
On the former point, Bruhwiler says that fixing leaks can help slash the emissions in the short term.
The latter finding, the researchers say, indicates that fossil fuel extraction is not behind the global uptick in methane emissions. But then, what is?
"We believe methane produced by microbial sources—cows, agriculture, landfills, wetlands, and fresh waters—are responsible for the increase, but we cannot yet pinpoint which are the primary drivers," lead author Stefan Schwietzke, a scientist with CIRES at the University of Colorado Boulder, said. "If the methane is mainly coming from cows or ag[riculture], then we could potentially do something about it. If it's coming from decaying vegetation in wetlands or fresh waters, then a warming climate could be the culprit, which means that it could be part of a self-reinforcing feedback loop leading to more climate change. Those are big ifs, and we need to figure them out."
A study published last month from watchdog group Oil Change International (OCI) in partnership with 14 other environmental organizations stated that "No new fossil fuel extraction or transportation infrastructure should be built, and governments should grant no new permits for them."
That's because "The potential carbon emissions from the oil, gas, and coal in the world's currently operating fields and mines would take us beyond 2°C of warming," the groups wrote.
"If the world is serious about achieving the goals agreed in Paris," said OCI executive director Stephen Kretzmann of the climate accord, "governments have to stop the expansion of the fossil fuel industry."