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IN A University of Colorado lab, near a furnace running at 1100°C and machines adorned with Star Trek posters, lie rows of metal flasks holding clues to the cause of an alarming rise in a powerful greenhouse gas. They contain samples of air from around the world that ‘s team of methane detectives analyse to reveal whether the gas came from burning fossil fuels and wood, or from wetlands and cow guts.

The work isn’t merely academic. Pinpointing the sources of the methane has become an urgent task: the gas may be shorter-lived than carbon dioxide, but its warming effect is 28 times more potent and atmospheric concentrations of it have resumed climbing inexorably upwards since 2007, after seeming to plateau in the early 2000s. We still aren’t sure why.

Worryingly, according to preliminary data released this month, last year, methane levels made their biggest annual jump, by , since records started in 1983. “2020’s increase was double the 2007 growth. It’s even higher than the early 1980s, when the gas industry was going crazy. It’s really scary,” says at Royal Holloway London. It is possible the coronavirus pandemic had a role, but this is still being investigated.

Whatever the cause, methane levels have raced ahead of most climate scientists’ scenarios. Even new modelling for a , due out in August, predicts that methane concentrations will start to fall this year, says at the Victoria University of Wellington, New Zealand. But that isn’t happening in reality.

Since the pre-industrial period, methane has contributed about 16 per cent of global warming. Tackling it matters if we want to avert catastrophic climate change. “In the long-term, we absolutely must reduce CO₂ emissions. However, on shorter timescales, of 25 years, methane is a really potent greenhouse. It provides a huge lever for near-term climate [change] and is really one of the best ways of keeping temperature rises below 1.5°C,” says at the University of Washington in Seattle, referring to the 2015 Paris Agreement‘s tougher goal.

Fixing the problem requires knowing what is driving the surge. Methane in the atmosphere can be traced back to a thermogenic source – the burning of methane locked up in fossil fuels – a pyrogenic one, such as burning wood, or a biogenic one, meaning microbes in wetlands, rice paddies, livestock, permafrost and landfill sites. Michel’s team is analysing the ratio of two isotopes of carbon in methane samples to pinpoint the sources.

Some research has blamed the US fracking boom, which coincided with the rise in methane. However, the methane in air flasks that Michel’s lab has sampled in recent years has less carbon-13 and more carbon-12, implying the growth is from microbial sources such as wetlands and agriculture. “Fossil fuels are definitely part of the picture. But it’s hard to explain our data without having an increase in biogenic methane,” says Michel.

Michel’s spectrometers can’t tell us whether the source is more cows, or wetlands behaving differently. However, big annual swings in methane levels, like 2020’s, are unlikely to be due to anthropogenic sources, be it cattle or fossil fuel extraction, says at the US National Oceanic and Atmospheric Administration.

Wetland emissions vary widely depending on temperature and rainfall. Wetlands in the tropics, such as northern Zambia and the Amazon, appear to be behind the increase, says Nisbet, who has analysed air samples from these regions. “The tropics are getting warmer and wetter,” he says.

Microbes produce more methane when it is warmer, which raises fears of a “climate feedback”, where warming begets more warming because higher temperatures make wetlands emit more of the powerful greenhouse gas. “What if subtle changes to temperature and precipitation are increasing natural emissions of methane?” says Dlugokencky. “That would be consistent with the observed isotopic signals. It would also complicate the challenge of reducing greenhouse emissions to stabilise the climate.”

Last year was one of the three warmest years on record, so methane-belching wetlands could partly explain 2020’s record methane jump. Another possibility, which Turner is investigating, is that the big falls in nitrogen oxide air pollution caused by covid-19 lockdowns had the knock-on effect of reducing levels of hydroxyl radicals in the atmosphere. Nitrogen oxides play a role in the formation of this molecule, which removes methane from the atmosphere. “My guess is that it’s a combination of both human-caused and natural factors,” says Turner.

“2020’s increase in methane was double the 2007 growth. It’s really scary”

In the face of possible climate feedbacks and accelerating growth, methane can look like an impossible roadblock to reaching the Paris climate goals. But there is an upside. “It’s in many ways easier to do something about methane than CO₂ and N₂O [nitrous oxide, the third main greenhouse gas],” says at Duke University in North Carolina.

Most N₂O comes from fertiliser used for growing crops, while burning CO₂ is so entangled in our economies that eliminating it is slow and difficult. Moreover, CO₂‘s long-lived nature means, even if emissions stopped today, we wouldn’t see a halt in rising temperatures for many decades.

By comparison, reducing methane could make a big difference to temperatures quickly. A (UNEP) found that a 45 per cent cut in methane emissions by 2030 would avoid nearly 0.3°C of warming by the 2040s. Another concluded that pursuing only the easiest methane cuts could avoid 0.25°C of warming by 2100.

About half of our methane emissions come from the fossil fuel industry – oil, coal and gas – while the other half is from agriculture and waste sites, says at the Laboratory for Sciences of Climate and Environment in France. Saunois, who runs the report, says there is little sign of serious action to cut methane emissions yet. “But there is hope,” she says. A quick fix would be countries banning uncovered landfills as the European Union has done, she says.

Finding leaks in oil and gas pipes and wells could greatly reduce emissions, says Turner. And we don’t have to focus on all oil and gas fields, but mainly the industry’s “superemitters”. Just 1 per cent of the industry’s methane sources accounts for 30 per cent of its emissions, says Turner. Moreover, about 40 to 45 per cent of methane abatement has no net cost, because firms can sell the gas instead, according to .

There are signs that big firms are taking the issue more seriously than smaller ones. BP, ExxonMobil and others have methane leak-reduction targets for 2025. The problem is in 2019 these firms accounted for less than 2 million tonnes of the 75 million tonnes of methane the industry emitted.

Stronger regulation is coming. The EU , and the US senate last month approved President Joe Biden’s decision to . Our ability to spot methane leaks from space is also rapidly improving, thanks to a flurry of new satellites (see “Methane eyes in the sky“).

There are other benefits to reducing methane levels: Shindell’s UNEP report found each million-tonne cut in methane prevents about 1430 annual premature deaths from ozone air pollution globally.

As Dlugokencky says, many ways of cutting methane emissions from the fossil fuel industry – including a shift to renewable energy and electric cars – would also have the benefit of reducing enemy number one: CO₂ emissions. We just need to get on with it.

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