Methane produced by oil exploration on the Fort Berthold Indian Reservation east of New Town, North Dakota, May 18, 2021. MATT BROWN/AP
It was a mystery that had fueled scientific debate and sparked concern on the front lines of the fight against the climate crisis. In 2020, concentrations of methane, a very potent greenhouse gas, experienced a spectacular increase (+ 50% compared to 2019), at that time the highest value recorded since atmospheric measurements began almost forty years ago. An unexpected jump when human activities were severely constrained by the restrictions related to the Covid-19 pandemic. A team of French, Chinese and American researchers has solved the mystery.
Their findings, published in Nature on Wednesday, December 14, highlight two main causes related to the decline in air pollution and the increase in methane emissions from wetlands under the influence of global warming. Two causes that could further exacerbate climate change in the form of runaway.
Methane, the second greenhouse gas after carbon dioxide, has a much higher warming potential than CO2: 28 times more in a hundred years and 82 times more in twenty years. It has been responsible for 30% of global warming since the pre-industrial era, and its emissions have skyrocketed in recent years, reaching around 600 million tons per year.
It comes 60% from human activities (agriculture, fossil fuels and waste) and 40% from natural sources (wetlands, etc.) “where microorganisms produce methane to feed themselves, in water-saturated and oxygen-poor areas,” recalls Marielle Saunois, researcher at the Laboratory of Climate and Environmental Sciences (LSCE) and one of the authors of the study. That Countless and diverse individual sources make the assessment of methane emissions more complex than that of CO2.
Higher natural emissions
From reviewing emission inventories, numerical models and measurements of atmospheric concentrations, scientists showed that half of the methane increase in 2020 compared to 2019 is explained by higher natural emissions, particularly in the northern hemisphere (tropics, boreal regions and Siberia). , which originate mainly from wetlands (swamps, bogs, etc.). “Microorganisms produce more methane in a warmer and wetter climate that we observed in 2020,” specifies Marielle Saunois.
The Arctic regions, whose permafrost (permanently frozen ground) is rich in methane, could also release more of it under the influence of warming, but this phenomenon played only a marginal role. “We are a long way from a methane bomb like we might have feared before,” assures Philippe Ciais, co-author of the study and climatologist at the LSCE.
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