While it typically remains in the atmosphere for much less time than CO2, methane is more potent – about 86 times more per unit of mass over 20 years, the paper noted.
“Particularly during the last few years, we’ve seen quite dramatic growth rates of methane,” said Pep Canadell, head of CSIRO’s Global Carbon Project and one of the paper’s authors.
Emissions of the gas from natural sources of methane, such as wetlands, termites or volcanoes, barely budged from the average over 2000-2006 to 2017, at about 367 million tonnes a year, the paper said.
By contrast, fossil-fuel sources had risen about 27 per cent to 135 million tonnes annually, with coal-linked methane emissions up 51.7 per cent and those from oil and gas up 16.7 per cent.
Methane from farming, such as rice cultivation and cattle, rose 12.7 per cent during the period to 213 million tonnes, annually, the paper found.
China was a big source of the extra methane as its coal industry expanded, Dr Canadell said. The Oceania region, which includes Australia, also featured as one region where both fossil fuel and agriculture-sourced methane has increased.
In North America, fossil-fuel development contributed about 80 per cent of the extra methane from that region.
Stanford University’s Rob Jackson, the paper’s lead author, said gas use “is rising quickly here in the US and globally”.
“It’s offsetting coal in the electricity sector and reducing carbon dioxide emissions, but increasing methane emissions in that sector,” he said. “The US and Canada are also producing more natural gas, and as a result, we’re emitting more methane from oil and gas wells and leaky pipelines.”
Proponents of the gas industry had long dubbed it a “transition fuel” to wean economies off coal, citing its lower warming impact when burnt. However, leakage of methane can nullify any advantage, given the potency of the gas in the atmosphere.
“Moving from one fossil fuel to another fossil fuel is not a pathway to net-zero emissions that we have collectively agreed on,” Dr Canadell said, referring to the 2015 Paris climate accord that sets a path for carbon neutrality by the second half of the century.
Methane was “not under any kind of policy” to be curbed, creating opportunities for governments to act, he said.
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Peter Hannam writes on environment issues for The Sydney Morning Herald and The Age.