Researchers at the University of Michigan recently released a timely study. These are key insights their findings provide into the increasing levels of atmospheric methane. This study, recently published in the journal Communications Earth & Environment, found a counterintuitive secret. Instead, it demonstrates that tropical wetland flooding likely is not driving the majority of the rapid rise in methane emissions observed between 2020 and 2022.
A recent study shows that atmospheric methane concentrations increased nearly every year from 2007-2019. During this time, the average annual growth rate peaked at more than 7.3 parts per billion (ppb). A worrisome trend began in 2020 with these growth rates doubling to 14.8 ppb. Unfortunately, this bleak scenario got worse in 2021, as evidenced by methane growth rates hitting their highest growth rate on record of 17.7 ppb. In 2022, methane concentrations decreased slightly to 13.1 ppb. Notwithstanding these local successes, the global picture is much more troubling, as methane concentrations continue an alarming rise in the atmosphere.
Methane Emissions from Wetlands
Wetlands are critical component in the global methane emissions picture, accounting for roughly 30–40% of total emissions. Tropical wetlands, especially, make up most of the methane released from these ecosystems. Ying Xiong, a U-M research fellow in climate and space sciences engineering, leads the research team. Using satellite and topographic data, they created the most comprehensive map of tropical inundation to date, allowing them to assess changes on a daily and monthly basis.
In fact, wetlands make up the largest and least understood share of global methane emissions. This study found that recent increases in methane concentration were not primarily driven by tropical wetland inundation or precipitation. This finding contradicts previous assumptions. Confirming earlier studies, it indicates that inundation in these areas is not the primary driver of the increase in atmospheric methane.
Insights from Satellite Data
This novel application of freely available satellite data allowed researchers to receive more comprehensive spatial detail about the heterogeneous inundation patterns that occur in tropical wetlands. The researchers were able to cross-reference the data with a global timeline of methane spikes. It presents strong, counterintuitive evidence that the inundation events probably did not lead to the substantial increase in atmospheric methane concentrations during this time.
Moreover, the study is a timely reminder of the need to understand the chemical behavior of methane in the atmosphere and across various time scales. Methane reacts chemically to form water vapor and carbon dioxide within approximately ten years, while carbon dioxide can linger for centuries, complicating efforts to mitigate climate change.
National Oceanic and Atmospheric Administration (NOAA) since 1983, conducting background atmospheric monitoring of methane. This year-over-year work has established a rich long-term time series that researchers can use to analyze trends and fluctuations. Preliminary values for 2025 are forthcoming after a series of recalibrations of standard gases and quality control procedures.
Implications for Climate Research
The results from this study hold promising and important implications for climate research and policy-making. Knowing the sources and drivers of methane emissions is essential for creating effective strategies to tackle such a short-lived but potent climate forcer. With atmospheric methane still climbing at dangerous rates, it’s crucial to find the right culprits to properly inform and develop targeted interventions.
Ying Xiong emphasized that while tropical wetlands are vital ecosystems, their role in methane emissions may not be as straightforward as previously thought. Ongoing research will be critical as we work to understand the complexities at play where methane dynamics contribute positive or negative feedbacks to global warming.