Environmental microbes caused more methane emissions than fossil fuels between 2020 and 2022, analysis finds

Environmental microbes, not fossil fuels, are to blame for the recent increase in global methane emissions, according to a detailed new analysis published October 28 in the journal. Proceedings of the National Academy of Sciences by CU Boulder researchers and collaborators.

“Understanding where methane comes from helps us guide effective mitigation strategies,” said Sylvia Michel, senior research assistant at the Institute for Arctic and Alpine Research (INSTAAR) and doctoral student in the Department of Atmospheric and Ocean Sciences from CU Boulder. . “We need to know more about these emissions to understand what kind of climate future we can expect.”

Methane is a powerful greenhouse gas responsible for about a third of global warming since industrialization. Although the atmosphere contains less methane than carbon dioxide, methane traps about 30 times more heat than carbon dioxide over a 100-year period, making it a critical target for combating climate change.

“Methane concentrations in the air have almost tripled since the 1700s,” said co-author Jianghanyang (Ben) Li, an assistant professor in the Department of Atmospheric and Ocean Sciences and INSTAAR.

But unlike CO₂which can remain in the atmosphere for thousands of years, methane degrades within a decade. As a result, tackling methane emissions can have an immediate and powerful impact on slowing the rate of warming, making it “low-hanging fruit,” Li said.

Although the results suggest that microbes are emitting more methane than fossil fuels in recent years, reducing fossil fuel consumption remains key to combating climate change, the team said. Reducing food waste and eating less red meat can also help reduce the methane footprint.

Identify the source

Previous research suggests that fossil fuel production is responsible for around 30% of global methane emissions.

But microbial sources – such as wetlands, livestock and landfills – are an even bigger source of methane, accounting for more than half of global emissions. Archaea, a type of microorganism living in soil and the intestines of cows, produce methane as a byproduct of the breakdown of organic matter.

Michel and Li have worked with the Global Monitoring Laboratory (GML) in Boulder within the National Oceanic and Atmospheric Administration (NOAA) for the past several years.

The lab receives air samples from 22 locations around the world every week or two. Researchers then isolate different components from the air, such as CO₂ or methane – for analysis.

By examining the types of carbon atoms, or isotopes, that the methane sample contains, Michel, Li and the team can identify the source. For example, methane from fossil fuels contains more carbon-13 isotopes than methane found in the air, and methane from microbial sources contains even less carbon-13. The laboratory has been measuring methane isotopes since 1998.

Scientists have observed a rapid increase in atmospheric methane levels since 2007, following a period of stabilization in the early 21st century. In 2020, NOAA reported the highest methane growth rate since it began collecting data in 1983, and that record was broken again in 2021.

At the same time, Michel noticed a surprising decrease in the carbon isotope 13 over the past 17 years. She and the team sought to understand what motivated him.

The culprit

Using computer simulations, Michel and his team modeled three different emissions scenarios to see which one would leave an isotopic signature similar to the one observed.

They found that between 2020 and 2022, the drastic increase in atmospheric methane was almost entirely due to microbial sources. Since 2007, scientists have observed that microbes play a significant role in methane emissions, but their contribution has increased to more than 90% as of 2020.

“Some previous studies have suggested that human activities, particularly fossil fuels, are the main source of methane growth in recent years,” said Xin (Lindsay) Lan, a scientist at the Cooperative Research Institute of Health Sciences. environment (CIRES) at CU Boulder. and NOAA. She leads NOAA’s Global Greenhouse Gas Trends Report at GML.

“These studies did not examine the isotopic profile of methane, which could lead to a different conclusion and an incomplete picture of global methane emissions.”

It remains unclear whether increased microbial emissions come from natural sources like wetlands or anthropogenic sources like landfills and agriculture. The team plans to do further research to identify the exact source of the methane.

“In a warming world, it wouldn’t be surprising if any of these sources were emitting more methane,” said Michel, who explained that microbes, like humans, tend to have higher metabolisms when ‘it’s hot. “As a result, more methane could remain in the atmosphere and accelerate global warming. So we need to tackle the climate crisis, and that really means tackling CO.₂ broadcasts.”