[Lead]
An international team of researchers, including scientists from Utrecht University and the University of Maryland, has reconstructed the concentration of clumped isotopes of methane in air from the past for the first time. This provides new insights into how atmospheric methane concentrations have changed since the start of the industrial era, around 1850. For the study, the scientists used air roughly forty years old, preserved in compacted snow (firn) in Greenland. The results were published in Science Advances .
[Intro]
Methane is the second most important greenhouse gas after CO2, responsible for around thirty percent of global warming to date. Atmospheric methane concentrations are rising, but it is not yet fully understood why that happens.
Human fingerprint
The researchers' measurements and analyses showed that the concentration of clumped methane isotopes, rare methane molecules with two heavy atoms clustered together, has changed significantly over the past decades. At first, the researchers couldn't fully explain this shift, but after running model simulations of the atmosphere spanning the last thousand years, they were able to pinpoint a cause. "Since the start of industrialisation, humans have disrupted the balance between methane emissions and breakdown so profoundly that it's visible in our measurements," explains Malavika Sivan, first author of the study.
Malavika Sivan , former researcher at IMAU and first author of the study: “ Since the start of industrialisation, humans have disrupted the balance between methane emissions and breakdown so much that it's visible in our measurements .”
Methane balance
The clumped isotope signal reflects the balance between how much methane is emitted and how much is removed from the atmosphere. That balance determines whether atmospheric methane concentrations keep rising or start to fall. With this information, researchers can reconstruct the methane balance over time, and going forward, allowing them to check whether measures taken to reduce methane emissions are working.
That matters, says Thomas Röckmann, professor of Atmospheric Physics and Chemistry. "Reducing methane concentrations is one of the fastest ways to slow global warming in the short term." Continued human emissions and possible climate feedback from natural sources could drive further increases. "Policy initiatives like the Global Methane Pledge, which aims for a thirty percent cut in methane emissions by 2030 compared to 2020, might help slow or reverse that trend," Röckmann explains.
Thomas Röckmann , professor of Atmospheric Physics and Chemistry: “ Reducing methane concentrations is one of the fastest ways to slow global warming in the short term .”
A surprising measurement
The research was prompted by an unexpected finding: the researchers measured clumped methane isotopes in the current atmosphere. The occurrence of these molecules was far higher than in methane from known sources such as wetlands, agriculture, and fossil fuels. Those sources couldn't account for such a strong signal.
The team concluded that the clumped isotope signal must originate from methane removal: when methane breaks down in the atmosphere through reactions with other substances. These clumped molecules react slower than normal methane molecules. “Following this, we wondered if we could use these clumped methane signatures to learn how the removal reactions changed in the atmosphere over time”, Röckmann explains.
Forty-year-old air
Methane is mainly released from biological and fossil sources. It forms naturally in wetlands, rice paddies, landfills, and agricultural systems, and is also released from fossil fuels such as coal, oil, and natural gas. To understand how methane sources and removal have changed over time, the researchers needed access to air from the past. And not just a little: analysing clumped methane isotopes requires as much as a thousand liters of air.
That old air can be found in firn: a layer of dense snow between the surface and the underlying glacial ice, where air remains trapped that is sometimes up to seventy years old. At the EastGRIP research station in Greenland, Röckmann collected the necessary air samples by drilling deep into the snow and essentially pumping the air out with specialised equipment. “We collected 500 to 700 litre air samples that were up to forty years old,” Röckmann says. “Analysing that air tells you a lot about the composition of the atmosphere in the past.”
An international collaboration
The amount of air was still on the low end for reaching the best precision with the instrument that is used in Utrecht. But a research group at the University of Maryland had a different instrument that could do the same measurements using less air. Sivan travelled to the University of Maryland for two months to analyse the air samples, together with her colleague Jiayang Sun. "There was a lot of trial and error, but in the end, we were excited to see such a strong temporal change in the clumped isotope signal.”
The results were unexpected, and it took a lot of discussion and modelling to understand the signal measured. “But it was worth it: we really understand how the clumped isotope signal records the influence of humans on the atmosphere in the industrial period" Sivan says.
Science Advances
Experimental study
Not applicable
Anthropogenic perturbations to atmospheric methane reflected in Greenland firn air clumped isotope measurements
15-Jul-2026