PARIS • A decade-long surge of the potent greenhouse gas methane threatens to make the fight against global warming even harder, according to top researchers.
"Additional attention is urgently needed to quantify and reduce methane emissions," said a summary of the findings of a consortium of 81 scientists in the Environmental Research Letters journal yesterday.
After rising slowly from 2000 to 2006, the concentration of methane in the air climbed 10 times more quickly in the following decade, according to that study, which was published in the peer-reviewed Earth System Science Data.
The unexpected - and largely unexplained - increase was especially sharp in 2014 and last year.
"Keeping global warming below 2 degrees Celsius is already a challenging target," the scientists said, referring to the goal set in the 196- nation Paris climate pact which took effect last month. "Such a target will become increasingly difficult if reductions in methane emissions are not also addressed strongly and rapidly."
On current trends, average global temperatures are on track to jump by more than 3 deg C by 2100, even if national carbon-cutting pledges annexed to the Paris Agreement are honoured. Without those pledges, the increase would be much higher.
To date, efforts to keep the planet from overheating have focused mostly on the main greenhouse gas, carbon dioxide, a by-product of burning fossil fuels that accounts for at least 70 per cent of warming.
But even as CO2 output has started to plateau, methane (CH4) emissions - responsible for about 20 per cent of the increase in global temperatures - are soaring.
Indeed, the pace of recent emissions aligns with the most pessimistic scenarios laid out by the United Nations' top science authority, the Intergovernmental Panel on Climate Change.
CH4 is 28 times more efficient than carbon dioxide at trapping the sun's heat. As with carbon dioxide, the Earth naturally absorbs and releases methane.
Even if scientists agree that total emissions of methane are rising sharply, they are uncertain as to why. Today, some 60 per cent of methane originates from human activity; the rest from wetlands and other natural sources. About a third of human-generated methane is a byproduct of the fossil fuel industry.
Researchers point to a surge in coal-generated power in China, along with leakage from the natural gas fracking boom in the US.
But coal-fired plants and fracking leaks are not sufficient to account for the jump in emissions.
A more likely culprit, the study concluded, is livestock production and agriculture, which together account for nearly two-thirds of man-made methane emissions.
A third possibility is a slowdown in the natural chemical reaction in the atmosphere that breaks down CH4.