Global emissions of methane have reached the highest levels on record, according to a new study.
This has been driven by coal mining, oil and natural gas production, cattle and sheep ranching and landfills, the researchers say, with more than half of all emissions now linked to human activities.
And unlike with carbon emissions, it’s unlikely they have fallen during the coronavirus pandemic.”We’re still heating our homes and buildings, and agriculture keeps growing,” says Rob Jackson from Stanford University, US, who heads the Global Carbon Project.
They show that methane emissions have been increasing by 50 million tonnes a year since the early 2000s, when concentrations in the atmosphere were relatively stable, reaching nearly 600 million tonnes in 2017, the last year for which complete data are available.
That’s akin to putting 350 million more cars on the world’s roads, the authors suggest.
Emissions have risen most sharply in Africa, the Middle East, China, South Asia and Oceania, with the US close behind. Only in Europe has there been a decrease over the past two decades.
“Policies and better management have reduced emissions from landfills, manure and other sources here in Europe. People are also eating less beef and more poultry and fish,” says Marielle Saunois of the Université de Versailles Saint-Quentin in France, lead author of the paper in Earth System Science Data.
Tropical and temperate regions have seen the biggest jump in methane emissions, the researchers say. Boreal and polar systems have played a lesser role.
And despite fears that melting in the Arctic may unlock a burst of methane from thawing permafrost, the researchers found no evidence of this through 2017.
Human-driven emissions are in many ways easier to pin down than those from natural sources, says Jackson.
“We have a surprisingly difficult time identifying where methane is emitted in the tropics and elsewhere because of daily to seasonal changes in how waterlogged soils are,” he says.
Aircraft, drones and satellites are making other work easier, however, and in particular show promise for monitoring methane from oil and gas wells, Jackson adds. “I’m optimistic that, in the next five years, we’ll make real progress in that area.”
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