20 de enero de 2025
Record Rise In Methane Emissions Linked To Wetlands Flooding
Study Reveals Surge In Wetland Methane Emissions Aligning With Rising Groundwater, La Niña And Regional Warming
Methane (CH4) is considered the second most important GHG contributing to global climate change. Both in-situ and satellite monitoring show this heat-trapping gas has been accumulating in the atmosphere over recent decades. In 2020 and 2021, the methane growth rate (MGR) in the atmosphere reached 15.2 ± 0.5 and 17.8 ± 0.5 parts per billion per year, hitting record highs since systematic monitoring began in the early 1980s. Despite reduced human activity during the global COVID-19 shutdown, methane levels continued to rise sharply. This acceleration of methane growth in the atmosphere reveals the emission surges from wetlands flooding, corresponding with rising groundwater during prolonged La Niña conditions. This rise poses a significant challenge to meeting the goals of the Paris Agreement to limit global warming.
Focus Of The Study
The study, funded by the ESA Climate Change Initiative's project and led by Dr. Xin Lin from Laboratoire des Sciences du Climat et de l’Environnement, analysed the CH4 emission changes and potential climate drivers using an ensemble of atmospheric inversions based on surface and satellite methane observations.
Atmospheric inversions are a method in which scientists use atmospheric observations and models to figure out where and how much greenhouse gases like methane are emitted and consumed by different regions and processes of the Earth system. The study combines bottom-up estimates and top-down atmospheric inversions. The bottom-up estimates are built on emission inventories of various natural or anthropogenic sources by aggregating data on activities and emissions factors, plus biogeochemical models that mechanistically simulate natural emission or uptake processes in wetlands or upland soils. Top-down estimates from atmospheric inversions are based on atmospheric CH4 measurements from in-situ monitoring networks or satellites with atmospheric transport models, from which scientists can work backward to infer distribution of methane sources and sinks. This approach allowed the researchers to identify changes in emissions in 2020 and 2021 compared to 2019 that highlight emissions from tropical and boreal flooded areas as the key contributors. The results have been published in the journal Nature Communications.
Methane (CH4) growth rates were derived from zonally averaged observations of NOAA Global Monitor Laboratory (NOAA/GML) marine boundary layer (MBL) sites and GOSAT total column CH4 (XCH4) observations.
Key Finding: Six Wetland Regions Accounted For Majority Of Global Methane Emission Increase In 2020 And 2021
The global methane emissions increased by 20.3±9.9 and 24.8±3.1 Tg CH₄ per year in 2020 and 2021. Methane increases were particularly pronounced in six major wetland regions: the Niger River Basin, Congo Basin, Sudd Swamp, Ganges floodplains, Southeast Asian deltas and the Hudson Bay lowlands. Together, these six wetland regions accounted for approximately 70% (14.1±4.2 Tg CH₄ per year) of the global methane emission increase in 2020 and 60% (14.9±2.6 Tg CH₄ per year) in 2021. These increases have coincided with rising groundwater levels, regional warming and prolonged La Niña conditions since 2020.
Fighting Global Warming Requires Better Understanding Of Wetlands
Wetlands are the largest natural source of methane, but their dynamics are still poorly understood. The study shows that methane emissions from wetlands have increased in recent times due to warmer and wetter conditions, which create an ideal environment for methane-producing microbes. This trend points to a potential positive climate feedback loop in which rising temperatures and flooding increase wetland methane emissions, further contributing to global warming. Scientists warn that simultaneous methane increases in tropical and boreal wetlands, such as those observed in 2020 and 2021, could become more common as warming increases and extreme or prolonged La Niña events become more frequent. Understanding how wetland methane emissions respond to climate variabilities is therefore crucial. “Our study shows that current biogeochemical models fail to capture methane emission surges in tropical wetlands revealed by atmospheric inversions”, adds Dr. Xin Lin, “stressing the need to integrate multiple data streams and modeling tools for better constraining emissions of tropical wetlands in the future”. These new findings also underscore the urgent need to reduce anthropogenic methane emissions to offset rising natural emissions and mitigate the risks of accelerated global warming. Atmospheric inversions constrained by ground-based or satellite observations can support quality control of national GHG inventory reports. The IPCC, for example, encourages to verify reported emissions against independent source of information, to promote transparency and align emissions reporting with real-world conditions.
Top-down versus bottom-up estimates of methane emission anomalies for eight tropical wetland regions. The open circles indicate two times the interannual variability of methane emissions during 2010-2019 from atmospheric inversions.
ESA CCI Projects Provide Valuable Insights for Policymakers and Researchers
The ESA Climate Change Initiative is a major R&D programme that harnesses data from multiple satellite missions to develop consistent, long-term observation records for 27 of the 55 key aspects of the climate. Also known as Essential Climate Variables, these data records form the fundamental basis of understanding the climate and tools used to anticipate future change and inform decision-making at global, national and local scales.
Funding for this study was provided by the ESA Climate Change Initiative's Regional Carbon Cycle Assessment and Processes (RECCAP-2) project, which aims to develop robust, observation-based estimates of changes in carbon storage and sinks and regional carbon budgets, and to provide science-based evidence for addressing climate change and its direct anthropogenic drivers. Research has also been supported by ESA project GHG-CCI.
Learn more: https://www.nature.com/articles/s41467-024-55266-y#citeas