Greenhouse gas methane just hit record high – so where is it coming from?

The amount of methane in the atmosphere passed the alarming milestone of 1,900 parts per billion in January.

Experts have since called for measures to limit emissions of the greenhouse gas, which is thought to have contributed 0.5C of warming since pre-industrial times, according to Nature.

Natural gas has become more popular as a relatively ‘clean’ fossil fuel, with demand soaring by up to 50% in recent decades, but the problem is not simply due to the fossil fuel industry, according to Euan Nisbet, professor of Earth sciences, Royal Holloway University of London.

Writing for The Conversation, Nisbet said: "Agriculture, producing about 150 million metric tons a year, is the largest overall source. As are urban landfills and sewage systems, contributing about 70 million metric tons annually."

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Nisbet says that scientists can monitor the sources of atmospheric methane by studying the proportion of two different isotopes of carbon - carbon-12 and carbon-13.

‘Biogenic’ methane, which comes from vegetation is high in carbon-12, while methane from fires and fossil fuels is richer in carbon-13.

"For two centuries, rapidly expanding gas, coal and oil industries steadily drove atmospheric methane richer in carbon-13. Since 2007, that trend has reversed, and the proportion of carbon-13 in atmospheric methane has decreased. Although fossil fuel emissions may still be growing, soaring methane emissions are now primarily the result of faster-growing biogenic sources," said Nisbet.

Nisbet added that the warming climate is leading to wetlands emitting more methane from rotting vegetation.

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He said that there are several obvious measures governments can take to combat methane emissions.

"Methane's short lifetime means that cutting emissions quickly reduces the greenhouse impact. Gas leaks are obvious targets, both at wells and in leaky street pipes. Ending the coal industry is an urgent global priority, not just to cut methane but also CO2 and air pollution.

"In the short-term, removing methane from coal mine air ventilation and cattle barns can be done as easily as certain pollutants are removed from car exhausts. Emissions from biodigesters will need stricter government regulation."

Research last year found that greenhouse gas emissions from dead trees in ‘ghost forests’ are known informally as ‘tree farts’ — but they are helping to drive climate change.

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‘Ghost forests’ often form when rising sea levels force salt water into forests, leaving dead and dying trees, still standing.

Researchers from North Carolina State University found that standing dead or dying trees in coastal wetland areas release greenhouse gases.

The researchers found that while dead and dying trees don’t release as much greenhouse gas as soil, they increase emissions from the ecosystem by about 25%.

Graduate student Melinda Martinez, of North Carolina State University, said: “Even though these standing dead trees are not emitting as much as the soils, they’re still emitting something, and they definitely need to be accounted for.”

“Even the smallest fart counts.”

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