Study Finds Tropical Wetland Flooding Not Responsible for Methane Spike

A recent study led by researchers at the University of Michigan has challenged the prevailing narrative regarding the substantial increase in atmospheric methane observed between 2020 and 2022. The study, published in the journal *Communications Earth & Environment* on July 8, 2025, indicates that the surge in methane levels was not primarily caused by emissions from tropical wetlands, as previously speculated. Instead, the research suggests that other sources or factors may be responsible for this alarming rise in greenhouse gas levels.

According to Ying Xiong, a research fellow in Climate and Space Sciences Engineering at the University of Michigan and the study's lead author, "Our work challenges the established view that the recent methane surge was primarily caused by tropical wetland emissions." Xiong emphasized that the dominant hydrological drivers, including inundation, precipitation, and terrestrial water storage, did not significantly contribute to the methane spike during this period.

Historically, atmospheric methane levels have steadily risen, with a noticeable increase starting in 2007. The growth rate averaged about 7.3 parts per billion (ppb) annually until it doubled to 14.8 ppb in 2020 and peaked at 17.7 ppb in 2021 before slightly declining to 13.1 ppb in 2022. This increase in methane, a potent greenhouse gas that contributes approximately one-third of the 1.2°C of warming since preindustrial times, raises concerns about its implications for global climate change.

The study utilized satellite data from the Cyclone Global Navigation Satellite System (CYGNSS), which was originally designed for hurricane research. This innovative approach allowed researchers to assess tropical inundation levels with high spatial resolution. They discovered that the expected correlation between wetland flooding and methane emissions was not supported by the data.

Eric Kort, a professor of Climate and Space Sciences Engineering at the University of Michigan and corresponding author of the study, stated, "Our work with CYGNSS shows how measurements of Earth from space can provide critical insights, sometimes beyond designed mission capabilities, to advance our understanding of how the Earth system is behaving."

While wetlands contribute approximately 30-40% of global methane emissions, the study's findings suggest that the focus should shift to other potential sources of methane. Xiong noted that emissions from agriculture, waste management, and non-hydrological controls in tropical wetlands—such as temperature and soil organic carbon availability—could be significant contributors to the recent methane increase.

The implications of this study are particularly critical as global efforts to mitigate climate change intensify. Understanding the precise sources of methane emissions is vital for developing effective strategies to reduce greenhouse gas levels and combat global warming. The research also highlights the importance of satellite technology in environmental monitoring, which can yield valuable data for climate science.

In conclusion, this study by the University of Michigan underscores the complexity of the climate system and the necessity for ongoing research to accurately identify the origins of greenhouse gas emissions. The findings call for a reevaluation of assumptions regarding the role of tropical wetlands in methane emissions and prompt further investigation into the various anthropogenic and natural factors that may influence atmospheric methane levels.

For more information, refer to the study by Ying Xiong et al., titled "Limited evidence that tropical inundation and precipitation powered the 2020-2022 methane surge," published in *Communications Earth & Environment* (2025). DOI: 10.1038/s43247-025-02438-3.