1114. Methane Surges in 2020-2022 Were Driven by Inundation of the Wet Tropics

The increase in methane gas in the atmosphere has accelerated over the past decade, with the highest increase on record from 2020 to 2022. A paper published in the journal PNAS showed that inundation of the wet tropics caused a methane surge in 2020-2022.

Major sources of methane include fossil fuels, livestock, paddy rice farming, wastewater, wetlands, and wildfires. On the other hand, tropospheric oxidation by hydroxyl radicals (OH) is a factor in the disappearance. Explanations for the rise in methane since 2007 include increased oil and gas emissions, increased livestock and wetland emissions, and lower OH concentrations.

Inverse analysis of satellite observations shows that methane emissions have progressed in the wet tropics over a decade (10 years), while they have decreased in the northern mid-latitudes. The surge from 2020 to 2022 was mainly due to emissions from equatorial Asia (43%) and Africa (30%), and that it was due to large-scale inundation associated with La Niña. In contrast, emissions from major anthropogenic emitters, such as the United States, Russia, and China, have remained relatively flat from 2010 to 2022. The concentration of OH (major methane sinks) in the troposphere did not show a long-term trend from 2010 to 2022, but decreased from 2020 to 2022, contributing to the surge in methane.

Africa accounted for 30% of the methane surge in 2020-2022, which may be due to the rapid expansion of livestock and rice cultivation. The regions with the largest increases in emissions (East Africa, Democratic Republic of the Congo, and Nigeria) account for 78% of Africa's wetland methane sources.

Equatorial Asia accounted for 43% of the surge in methane emissions from 2020 to 2022. Wetlands account for 50-65% of methane emissions in the region. In 2020 and 2021, equatorial Asia recorded the highest rainfall in the last decade, resulting in devastating floods. Rice cultivation was the largest contributor to the increase in anthropogenic emissions in equatorial Asia from 2010-2019 to 2020-2022, followed by waste, oil and gas, and livestock.

The prelude of the wet tropics in the methane emission trend is important for finding a path to contribute to climate change mitigation by reducing methane in the atmosphere.

Reference
Zhen Qu et al, Inverse modeling of 2010–2022 satellite observations shows that inundation of the wet tropics drove the 2020–2022 methane surge, Proceedings of the National Academy of Sciences (2024). https://www.pnas.org/doi/10.1073/pnas.2402730121

Contributor: IIYAMA Miyuki, Information Program