Global emissions of methane, a greenhouse gas multiple times more potent than carbon dioxide, rose by 9 percent in the decade through 2017, putting Earth on a track to warm by more than 3 degrees Celsius by the end of the century, according to an international study scheduled to be released Wednesday.
Atmospheric levels of the gas — emitted by digesting cows, leaky gas pipelines and natural sources such as wetlands — have increased 2½ times from pre-industrial levels, researcher Marielle Saunois said in a press briefing in Paris. Human activity accounts for about 60 percent of methane emissions, led by growing herds of livestock and emissions linked to oil and gas production.
Methane’s warming potential over a century is 28 times that of an equivalent mass of CO2, the researchers said. The current path of methane emissions lies between the two warmest scenarios used in projections by the Intergovernmental Panel on Climate Change, implying large cuts are needed to meet Paris agreement targets. Warming by 3 degrees would be double the rate scientists have identified as needed to constrain the worst impacts of climate change.
“We’re on track for a scenario that is rather hot, and above 3 to 4 degrees,” Saunois said in her presentation of the study. “Emissions are rising, particularly in tropical zones.”
After stabilizing in the late 1990s and early 2000s, methane emissions have been rising since 2007, accelerating since 2014, according to the study. Average annual emissions of methane rose to an estimated 596 million tons in the period through 2017, from 546 million tons in the 2000-2006 period.
The study, the work of more than 90 researchers as part of the Global Carbon Project, was published in the journal Earth Systems Science Data. A related paper on methane sources published in Environmental Research Letters found agriculture and fossil fuels were the main drivers behind increased emissions.
Methane — chemical formula CH4 — is responsible for about 23 percent of all warming produced by greenhouse gases so far, the researchers said. Its lifetime in the atmosphere of around nine years makes the gas a good target for climate change mitigation. Stabilizing or reducing emissions would have an impact on global warming within a few decades, they said.
Tropical regions were the source of 64 percent of global methane emissions, while northern high latitudes contributed 4 percent. The study didn’t find a significant effect from melting permafrost, though Saunois said “if the permafrost melts strongly, the emissions will increase.”
Agriculture and waste represented 56 percent of anthropogenic methane emissions, mainly linked to growing numbers of ruminant livestock that burp it up as they digest, the study found. Contributions from Asia and Africa increased as livestock herds expanded there, Saunois said. Europe was the only region to lower methane emissions over the period, helped by a drop in dairy cattle numbers and changes in how farms store and treat manure.
Production and use of fossil fuels accounted on average for 35 percent of emissions linked to human activity. Oil and gas accounted for almost two-thirds of the fossil emissions, notably leaks during drilling of wells and from cast-iron natural gas distribution grids in older cities. Coal mining made up most of the remainder, mainly due to methane pumped from mine-ventilation shafts.
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