"Additional attention is urgently needed to quantify and reduce methane emissions," they wrote Monday in the Environmental Research Letters journal, summarizing the findings of a consortium of 81 scientists.

After rising slowly from 2000 to 2006, the concentration of methane in the air climbed 10 times more quickly 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 2015.

"Keeping global warming below two degrees Celsius (3.6 degrees Fahrenheit) is already a challenging target," they said, referring to the goal set in the 196 nation Paris climate pact, which entered into force last month.

"Such a target will become increasingly difficult if reductions in methane emissions are not also addressed strongly and rapidly."

With only 1 degree Celsius (1.8 F) of warming above pre-industrial era levels so far, the world has seen an uptick in extreme weather, including droughts, superstorms, heat waves and coastal flooding boosted by rising seas.

On current trends, average global temperatures are on track to jump by more than 3 degrees Celsius (5.4 F) 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 percent of warming.

But even as CO2 output has started to plateau, methane (CH4), responsible for about 20 percent of the increase in global temperatures, is soaring.

Indeed, the pace of recent emissions aligns with the most pessimistic scenarios laid out by the UN's top science authority, the Intergovernmental Panel on Climate Change.

CH4 is 28 times more efficient at trapping the sun's heat. As with carbon dioxide, Earth naturally absorbs and releases methane.