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Researchers can now find out where this greenhouse gas comes from

Researchers have gained a clearer picture of why the amount of methane in the atmosphere has increased and where it comes from.

Wetland and forest pond under a blue sky with reflections in still water.
Landscapes like these are a major source of the increase in atmospheric methane.
Christine Forsetlund Solbakken Head of Communications
Presented by: Presented by: NILU
Published

One additional type of measurement can help reveal whether methane comes from microbes in wetlands, fossil fuels, or other sources. That is the finding of a new study.

The increase in atmospheric methane mainly comes from bacteria in wetlands, according to research Cathrine Lund Myhre has taken part in.

Methane is one of the most important greenhouse gases. After a stable period, methane levels began rising again in 2006. It has been difficult to determine exactly where the additional methane has been coming from.

Wetland emissions are increasing the most

It now appears that the rise can primarily be explained by growing methane emissions from wetlands. This is one of the main findings of the new study, which was carried out by researchers from Utrecht University, the California Institute of Technology, and NILU, among others.

Emissions from fossil fuel also increased, but not as much. At the same time, methane emissions from biomass burning declined. Changes from agriculture and waste were smaller and more variable.

“Our results suggest that methane from microbes has played the largest role in the renewed growth of atmospheric methane since 2006," says Cathrine Lund Myhre. She is the head of NILU's Centre for Atmospheric Data.

Myhre is referring to bacteria in the soils of wetlands, cow stomachs, agricultural waste, and landfills.

"Climate change has led to changes in wetlands at both low and high latitudes,” she says.

What is an isotope?

Atoms with the same number of protons but different numbers of neutrons are called isotopes. They have nearly identical chemical properties but differ in mass and therefore in their physical properties.

Source: International Atomic Energy Agency

35 years of measurements + a computer model

The researchers found that one extra type of measurement, used together with existing methods, can provide a much clearer picture.

By adding information from hydrogen isotopes in methane, they were able to distinguish between emissions released from microbes and emissions from fossil fuels.

The researchers combined 35 years of atmospheric measurements with a computer model that estimates how much methane is emitted by different sources around the world.

The model includes data on emissions from microbes in wetlands, as well as agriculture, fossil fuels, biomass burning, and waste. It also includes data on the processes that remove methane from the atmosphere. These are chemical processes driven by sunlight.

Two different fingerprints

Senior scientist Stephen Platt at NILU explains that the study's most important advance was using two different isotopic ‘fingerprints’ of methane.

Hydrogen isotopes and carbon isotopes

When researchers analyse methane in the atmosphere, isotopes provide information about where the methane comes from and what has happened to it in the atmosphere.

The difference between the two is which element's isotopes are being measured. Hydrogen isotopes are more difficult to measure than carbon isotopes, but they provide an additional layer of information that helps distinguish between the sources and the atmospheric fate of methane.

We can compare it to trying to identify a suspect from a somewhat unclear fingerprint from only one finger. Several people's prints might look similar. Adding hydrogen isotopes is like adding a fingerprint from another finger – it doesn't tell you something completely different, but together the two measurements make it much easier to identify the correct source.

With the additional data, the model became better at estimating methane emissions. It could also more accurately distinguish between natural and human sources – specifically the emissions from wetlands and emissions associated with fossil fuels.

The research team also improved estimates of how methane is removed from the atmosphere. Using the new measurements, the researchers gained a better understanding of these processes. They now estimate a slightly shorter lifetime for methane in the atmosphere over the Northern Hemisphere.

Portrait photo of Stephen Platt
Stephen Platt from NILU explains that the key advance in the study was using two different isotopic ‘fingerprints’ of methane.

The new measurements do not replace existing methods. Instead, they complement and strengthen them. By combining carbon and hydrogen isotope measurements, researchers can better test different explanations for changes in atmospheric methane. They can also reduce the uncertainty in their estimates.

Added to the monitoring programme

“The hydrogen isotope measurements add valuable new information that help us separate different methane sources. From now on, we will also report hydrogen isotopes in methane in the Norwegian monitoring programme for greenhouse gases,” says Platt.

The researchers conclude that long-term measurements of hydrogen isotopes in methane are an important tool for studying the global methane cycle. Researchers can gain a better understanding of where methane comes from, how emissions change over time, and how methane is processed in the atmosphere.

Methane plays a major role in climate change. Identifying its sources will therefore provide greater insight into both the Earth's changing atmosphere and its response to climate change.

Reference:

Dasgupta et al. Global methane emission estimates from a dual-isotope inversion: new constraints from δD-CH4, Atmospheric Chemistry and Physics, 2026. DOI: 10.5194/acp-26-8601-2026

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