Study finds fossil fuel methane emissions greater than previously estimated
But energy development is not responsible for global methane uptick
Methane emissions from fossil fuel development around the world are up to 60 percent greater than estimated by previous studies, according to new research led by scientists from NOAA and CIRES. The study found that fossil fuel activities contribute between 132 million and 165 million tons of the 623 million tons of methane emitted by all sources every year. That's about 20 to 25 percent of total global methane emissions, and 20 to 60 percent more than previous studies estimated.
However, the findings also confirm other work by NOAA scientists that conclude fossil fuel facilities are not directly responsible for the increased rate of global atmospheric methane emissions measured in the atmosphere since 2007.
"We recognize the findings might seem counterintuitive – methane emissions from fossil fuel development have been dramatically underestimated – but they're not directly responsible for the increase in total methane emissions observed since 2007," said lead author Stefan Schwietzke, a CIRES scientist working at ESRL's Global Monitoring Division.
The upward revision in the estimate of fossil fuel methane emissions comes despite improvements in industry practices that has reduced leaks from oil and gas facilities from about 8 percent of production to about 2 percent over the past three decades. Dramatic production increases have canceled out efficiency gains however, keeping the overall contribution from fossil fuel activities constant.
The research, published today in the journal Nature, analyzed the largest database of methane measurements ever assembled to determine how much methane is coming from fossil fuel development, natural geologic sources, microbial activity, and biomass burning.
After carbon dioxide, methane is the second largest contributor to global warming. While not as abundant or as long-lived as CO2, methane is 28 times more effective at trapping heat in the Earth's atmosphere over a 100-year time span. Reducing methane emissions from fossil fuel activities could be a cost-effective strategy to slow the rate of global warming during the next century, the authors said.
"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 NOAA research scientist. "The good news is that fixing leaking oil and gas infrastructure is a very effective short-term way to reduce emissions of this important greenhouse gas."
Schwietzke and his team, which included scientists from the University of Colorado and other universities, assembled a database roughly 100 times larger than previous ones. That improved the accuracy of their results, he said.
"A key message is that the number and comprehensiveness of measurements matter," said Schwietzke. "The models used to estimate methane emissions are very sensitive to the data we supply them with. Our method is based very strongly on empirical data to reduce the number of assumptions that influence results."
Methane emissions have distinct isotopic signatures that distinguish whether a sample came from fossil fuel development and natural geologic sources, microbial activity, or biomass burning.
Though the new estimates of fossil fuel emissions represent a major adjustment of the global methane budget, the study results support other research findings on another methane-related subject: what's causing the global uptick in atmospheric methane levels observed since 2007.
Isotopic analysis points to natural or human-caused microbial sources as the source of between 364 million to 419 million tons of methane per year, or 58 to 67 percent of methane released to the atmosphere each year, Schwietzke said. Total methane emissions from all sources increased by about 28 million tons per year between 2007 and 2013.
"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," he said. "If the methane is mainly coming from cows or ag, 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."
Future research, Schwietzke said, would benefit from enlarging the database to add samples from microbial sources like cows, agriculture, and wetlands. More data would help further reduce uncertainty about contributions from all methane sources, including fossil fuels, and would help better quantify the individual sources at continental scales.