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The lead author said that one positive implication of the research is "if we can reduce our emissions, it's going to have more of an impact."
A study published Wednesday in the journal Nature found that extraction and use of fossil fuels may emit up to 40% more climate-heating methane than previously thought-underscoring humanity's ability to significantly limit global temperature rise by rapidly transitioning to renewable energy.
While methane doesn't stay in the atmosphere nearly as long as carbon dioxide, it is 84-87 times more potent over a 20-year period. The latest update from the World Meteorological Organization (WMO) in November 2019 showed that globally averaged concentrations of the top two greenhouse gases increased in 2018.
"If we stopped emitting all carbon dioxide today, high carbon dioxide levels in the atmosphere would still persist for a long time," explained University of Rochester researcher Benjamin Hmiel, lead author of the new paper (pdf). "Methane is important to study because if we make changes to our current methane emissions, it's going to reflect more quickly."
Hmiel's team focused on emissions of fossil methane, "which has been sequestered for millions of years in ancient hydrocarbon deposits." As Carbon Brief reported:
These are most commonly associated with the extraction and transport of fossil fuels-such as leaks from coal mining and flaring from oil and gas drilling-but they have "natural" sources as well.
There are four main ways that fossil methane escapes into the atmosphere naturally. These include onshore seeps (including oil and gas seeps, mud volcanoes, and gas-bearing springs), submarine (offshore) seeps, "diffuse microseepage" from oil and gas-bearing sedimentary rocks, and geothermal and volcanic formations.
The new study suggests that the amount of methane being emitted in these natural ways has been overestimated.
Specifically, the researchers concluded from examining air bubbles in ice cores from Greenland that "natural" fossil methane emissions are about 10 times lower and emissions from human activity-namely, fossil fuel use and extraction-are 25-40% higher than previous research has shown.
Their findings, Hmiel told Carbon Brief, suggest that "almost all fossil methane in the atmosphere today is from anthropogenic emissions originating from the extraction and use of fossil fuels." However, he added, that also "puts more of the emissions under our domain and agency."
As the lead author put it in the university's statement: "I don't want to get too hopeless on this because my data does have a positive implication: most of the methane emissions are anthropogenic, so we have more control. If we can reduce our emissions, it's going to have more of an impact."
Although he was not involved in the new research, Joeri Rogelj concurred with Hmiel in a statement. Rogelj, a lecturer at the Grantham Institute at Imperial College London, was coordinating lead author of a major climate report the United Nations' Intergovernmental Panel on Climate Change published in October 2018.
"This new study brings both good and bad news for our ability to keep global warming in check," Rogelj said Wednesday. "The bad news is that this study shows that human activities might well be responsible for a much larger share of the increasing methane concentrations in the atmosphere."
The good news is that this study "shows us where we can act on climate change," he continued. "Measures and policies to eliminate methane emissions from fossil fuels are well known, and in many cases even make sense from a narrow economic perspective. They range from eliminating leaking pipes, reducing or improving flaring, and evidently also a shift away from the extraction and use of fossil fuels towards renewable energy sources."
"What this study shows is that we can have a bigger impact on methane in the atmosphere than earlier thought. This allows us to set climate policy priorities right," Rogelj added. "Together with bringing down carbon dioxide emissions to zero, keeping methane emissions to as low as possible levels will result in stabilizing global warming. Trying to reverse our global warming contribution will require us to draw down carbon dioxide from the atmosphere."
Despite the optimistic response to the research from Rogelj and some other experts, a scientist who spoke with ScienceNews Wednesday indicated that more work needs to be done to understand methane emissions from human activity:
[S]uch ice core-based work is not yet proven to be the most accurate technique to estimate natural geologic emissions, says Stefan Schwietzke, an environmental scientist with the Environmental Defense Fund who is based in Berlin. The ice core information is useful because it gives an immediate global snapshot of methane emissions, but "it has the challenge of interpretation and a lot of very complex analysis," Schwietzke says.
Direct measurements of methane emitted from different seeps or over mud volcanoes suggest much larger natural emissions, he adds. The problem with this method, however, is that it's difficult to scale up from local measurements to a global number. "To really understand the magnitudes, these two methods need to be reconciled. That hasn't happened yet."
Schwietzke and other researchers have proposed using airborne remote sensing to try to reconcile the two techniques. Airborne measurements can give a bigger-picture estimate, while also identifying local hot spots. Scientists have already been using this work to identify sources such as leaking pipelines, landfills, or dairy farms. Similar projects are tracking methane emission hot spots in Arctic permafrost.
Ultimately, despite the debate over technique, Schwietzke agreed that human activity has dramatically increased atmospheric methane in recent decades and "reducing those emissions will reduce warming."
