Methane is a worse greenhouse gas than carbon dioxide Gary Greenberg/Getty
Levels of a powerful greenhouse gas jumped again last year, continuing a surge in the past few years that researchers still cannot fully explain.
Atmospheric concentrations of methane climbed by 10.77 parts per billion in 2018, the second highest annual increase in the past two decades, according to .
Methane is a shorter-lived but much more powerful greenhouse than carbon dioxide. The amount finding its way from human and natural sources, which can include everything from oil and gas wells to wetlands, has been rising since 2007. The rate has accelerated in the past four years.
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Researchers 聽that if methane levels keep increasing at current rates then the Paris climate deal鈥檚 goals – of limiting global warming to 2掳C and pursuing efforts to keep below 1.5掳C – would be very difficult to meet.
Euan Nisbet of Royal Holloway University of London says researchers are very worried about the latest rise. Perhaps even more concerning is the fact no one is entirely sure what is driving the trend.
鈥淭he disturbing aspect is, we do not know which processes are responsible for methane increasing as rapidly as it is,鈥 says Ed Dlugokencky of the US’s National Oceanic and Atmospheric Administration.
Keith Shine at Reading University echoes that view. 鈥淭he fact that growth rates in the atmospheric concentrations of methane are approaching the levels we saw in the 1980s, after a period of relatively slow growth, is deeply concerning. The fact that we don鈥檛 understand the reasons for this surge deepen that concern.鈥
One possibility is that a warmer world is causing more methane to be released from wetlands in the tropics, fuelling even more warming. That would suggest a feedback loop is underway. 鈥淚鈥檓 not sure but it looks as if the warming is feeding the warming,鈥 says Nisbet. More evidence is needed to prove the idea though. Methane emissions chart New 女生小视频 / NOAA
Rebecca Fisher of Royal Holloway University of London says: 鈥淲e still do not know whether the growth is primarily an increase in ‘natural’ emissions, such as from warmer or wetter wetlands, or increased anthropogenic emissions such as rice agriculture or fossil fuels.鈥 It could also be a change in the atmospheric sinks of methane or, she says, most likely a combination of reasons.
The methane surge gains added significance from the fact researchers have been that the gas has a more powerful warming effect than previously thought. In the first report by the UN climate science panel, in 1990, one tonne of methane was considered to have 21 times the聽聽of one tonne of carbon dioxide. That was upgraded to 28 times聽, and could rise as high as 35 times in the next big assessment in 2022.
Article amended on 28 May 2019
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