A surge in methane emissions pushed atmospheric levels to a record high last year, which researchers say is a “very concerning” development for the planet.
The average atmospheric concentration of methane, a potent warming gas, recorded its biggest ever one-year jump last year, according to data from the US National Oceanic and Atmospheric Administration.
“In the last couple years we’ve seen a very, very large annual increase,” said Xin Lan, atmospheric scientist at the NOAA global monitoring laboratory. “That’s the large signal that gets us really concerned.”
Global average methane concentrations reached 1,896 parts per billion in 2021, up 15 per cent on the average during the 1984-2006 period, and 162 per cent higher than pre-industrial levels, NOAA said.
Methane emissions derive from natural sources as well as human activities. The gas leaks from gas pipelines and coal mines, and is produced by cattle, landfills, waste treatment facilities, wetlands and rice paddies.
The cause of the methane surge that began 15 years ago has not yet been identified. One hypothesis is that more methane is being emitted as the planet warms, as rainfall increases in methane-producing tropical wetland areas.
The chemical composition of atmospheric methane suggests emissions from biological sources have risen faster than those from fossil fuels.
By measuring the ratio of carbon 12 to carbon 13 found in methane molecules in the atmosphere, scientists can tell that natural sources, also known as “microbial” sources, have been increasing fast.
A UN Environment Program study published last year concluded that roughly a third of human-related methane emissions come from fossil fuel industries and about a fifth comes from waste and water.
“To figure out what sources are contributing to [the increase], is really an ongoing research question,” said Lan. “The challenge . . . is that we still can’t separate the human contributions to microbial sources, like livestock and waste, from the natural wetland [sources],” she said.
Carbon dioxide is the biggest single contributor to global warming but methane is much more potent, with about 80 times the warming potential of carbon dioxide on a 20-year basis. It also has a shorter lifespan in the atmosphere than CO2.
The world has warmed about 1.1C since pre-industrial times, with methane contributing about one-third of that.
Durwood Zaelke, president of the US-based Institute for Governance and Sustainable Development think-tank, said reducing methane emissions was the fastest way to slow global warming.
Last year, more than 100 countries pledged to cut their methane emissions by 30 per cent this decade.
The latest data are a worrying sign that the planet itself has started to emit more methane, Zaelke added.
“The most disturbing part is that the increases from natural sources is going to be harder to control,” he said. “How do you control methane emissions from a wetland?”