New research indicates that microorganisms thriving in landfills, agricultural fields, and wetlands are significantly contributing to alarming increases in atmospheric methane, a powerful greenhouse gas.
According to a comprehensive analysis released on October 21 by researchers from CU Boulder and their partners, it’s not fossil fuels but environmental microbes that have fueled the recent spike in global methane emissions.
“Identifying the sources of methane is essential for developing effective strategies to mitigate its impact,” explained Sylvia Michel, a senior research assistant at the Institute of Arctic and Alpine Research (INSTAAR) and a doctoral candidate in CU Boulder’s Department of Atmospheric and Oceanic Sciences. “A clear understanding of these emissions is crucial for predicting our climate future.”
Methane is an extremely effective greenhouse gas, being responsible for roughly one-third of the Earth’s warming since the onset of industrial activities. While the concentration of methane in the atmosphere is lower than that of carbon dioxide, it traps heat about 30 times more efficiently than carbon dioxide over a century, making it an important focus for combatting climate change.
“Methane levels in the atmosphere have nearly tripled since the 1700s,” stated co-author Jianghanyang (Ben) Li, an assistant professor in the Department of Atmospheric and Oceanic Sciences and INSTAAR.
Unlike CO2, which can linger in the atmosphere for thousands of years, methane breaks down within approximately ten years. Therefore, tackling methane emissions could lead to immediate and significant benefits in slowing global warming, which Li refers to as a “low-hanging fruit.”
While this research suggests that microbes have been the leading contributors to recent methane increases, the team emphasized that reducing fossil fuel use is still vital in the fight against climate change. Additionally, minimizing food waste and reducing red meat consumption can contribute to a smaller methane footprint.
Identify the source
Earlier studies estimate that about 30% of global methane emissions stem from fossil fuel production.
However, microbial sources—including wetlands, livestock, and landfills—account for a more substantial portion, representing over half of global methane emissions. Archaea, a type of microorganism found in soil and the digestive systems of animals like cows, produce methane as they decompose organic matter.
Over the past few years, Michel and Li have collaborated with Boulder’s Global Monitoring Laboratory (GML) at the National Oceanic and Atmospheric Administration (NOAA).
Every week or two, this lab receives air samples from 22 global locations. Researchers separate various air components—like CO2 and methane—to analyze. By studying the carbon isotopes within the methane samples, Michel, Li, and their colleagues can trace the methane’s origin. For instance, methane derived from fossil fuels has a higher concentration of carbon-13 isotope than that from microbial sources, which is typically lower in carbon-13. Since 1998, the lab has been measuring these methane isotopes.
A significant rise in atmospheric methane levels has been noted since 2007 after a phase of stability early in the 21st century. Notably, in 2020, NOAA reported the largest increase in methane levels since it began tracking in 1983, and this record was surpassed in 2021.
During this time, Michel observed an unexpected decline in carbon-13 isotopes over the last 17 years. This prompted her and her team to investigate the underlying reasons.
The cause
Using computer simulations, Michel and her colleagues modeled three scenarios of emissions to ascertain which might correspond to the observed isotopic signature.
The findings revealed that the alarming rise in atmospheric methane from 2020 to 2022 was primarily attributed to microbial sources. Although previous studies recognized the role of microbes in methane emissions after 2007, their contribution dramatically increased to over 90% beginning in 2020.
“Some earlier studies suggested that human activities, particularly fossil fuels, were the main contributors to recent methane growth,” noted Xin (Lindsay) Lan, a scientist at CU Boulder’s Cooperative Institute for Research in Environmental Sciences (CIRES) and NOAA. She leads NOAA’s reporting on global greenhouse gas trends at GML. “These investigations generally overlooked the isotope profiles of methane, which could result in a misleading and incomplete understanding of global methane emissions.”
It remains uncertain whether the increased microbial emissions are stemming from natural sources like wetlands or human-driven sources such as landfills and intensive agriculture. The research team aims to investigate further to pinpoint the specific sources of methane.
“In a warming environment, it wouldn’t be surprising if any of these sources emitted higher amounts of methane,” Michel stated, highlighting that, similar to humans, warmer temperatures can cause microbes to have higher metabolic rates. “As a result, more methane could accumulate in the atmosphere, exacerbating global warming. Thus, addressing the climate crisis necessitates a concerted effort to reduce CO2 emissions.”
