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A 2021 pledge by more than 100 nations to cut methane emissions from man-made sources by 30 percent by 2030 may not slow global warming as much as predicted, as new research shows that feedbacks in the climate system are amplifying methane emissions from natural sources, particularly tropical wetlands.
A new hot spot is the Arctic, where scientists recently found unexpectedly high winter methane emissions. And around the world, the increase in water vapor caused by global warming is slowing the rate at which methane decays in the atmosphere. If these feedbacks strengthen, scientists say, efforts to reduce methane from fossil fuels and other human sources could become obsolete.
Methane stores about 80 times more heat than carbon dioxide over a 20-year period. Scientists estimate that it is responsible for 20 to 30 percent of global warming since the beginning of the industrial age, when methane concentrations in the atmosphere were about 0.7 ppm. Since then, levels have risen sharply, peaking with the first fossil gas boom in the 1980s, then stagnating slightly before a huge increase began in the early 2000s. The amount of methane in the atmosphere reached about 1.9 ppm in 2023, almost three times the pre-industrial level.
About 60 percent of methane emissions come from fossil fuel use, agriculture, landfills and waste, with the rest coming from decaying vegetation in wetlands in the tropics and Northern Hemisphere. In a paper published July 30 in Frontiers in Science, an international team of researchers wrote that “rapid reductions in methane emissions this decade are essential to slow warming in the near future… and keep low-warming carbon budgets within reach.”
The scientists concluded that the abrupt increase in methane emissions in the early 2000s was probably mainly due to the response of wetlands to warming, with additional contributions from fossil fuel use. “This means that anthropogenic emissions must decline more than expected to reach a given warming target.”
Increasing rainfall – a well-documented effect of global warming – is causing wetlands to become larger and wetter. In addition, a warmer world encourages greater plant growth, which in turn means more decaying material that releases methane.
The increase in methane from natural sources should spur even greater efforts to cut emissions wherever possible, including from fossil fuel use and agriculture, said lead author Drew Shindell, a geoscientist at Duke University's Nicholas School of the Environment.
Recent measurements from a specially equipped jet show that methane emissions from oil and gas production in the U.S. are more than four times higher than EPA estimates and eight times higher than fossil fuel industry targets. Tackling methane emissions from anthropogenic sources is a critical part of the climate change equation, Shindell said, including emissions from agriculture.
“If we were to reduce these emissions, we would see a significant decline in atmospheric concentrations,” he said. “But reducing emissions from agriculture in particular is unlikely in the short term and perhaps not even in the long term.”
The study reiterated that rapid methane reductions are “essential to slow warming in the near future, limit overshoot by mid-century, and keep carbon budgets within reach for low warming rates.” The researchers noted that the cost of reducing methane emissions is small compared to many other climate mitigation measures and that “legally binding regulations and broad pricing are needed” to encourage the necessary drastic reductions.
Study finds new methane sources in dry permafrost
Scientists determine the source of methane by studying its carbon isotopes. Since 2007, these analyses show that the signal for methane from biological sources “has become significantly stronger,” says Euan Nisbet, an atmospheric scientist and methane expert at the University of Cambridge who was not involved in the new study.
“There are two explanations, both of which are probably correct,” he said. “One is that there are a lot more cows snorting. The other is that the natural wetlands are being activated. That happens first in the tropics, and then the permafrost melts in Canada, and suddenly you get all kinds of methane emissions from the Canadian and Siberian swamps when they get wet.”
Even cold, dry regions in the Arctic are contributing more to climate-warming methane pollution than previously thought, according to a paper published July 18 in Nature Communications. The paper examined dry permafrost areas known as Yedoma-Taliks highlands, which are found predominantly in northern Siberia. Thawing permafrost there is likely to accelerate methane production as microbes decompose organic material.