Atmospheric methane concentrations rose at an unprecedented rate in the early 2020s, driven by a weakened natural removal process and increased emissions from wetter landscapes. Scientists attribute much of the spike to a drop in hydroxyl radicals during 2020-2021, combined with climate-driven boosts from wetlands and agriculture. The findings underscore the interplay between atmospheric chemistry and weather patterns in global greenhouse gas trends.
Methane, the second-most important greenhouse gas after carbon dioxide, accumulated rapidly in Earth's atmosphere starting in 2020. Researchers from an international team, including Hanqin Tian from Boston College, published their analysis in the journal Science, detailing how levels climbed by 55 parts per billion from 2019 to 2023, reaching a record 1,921 ppb in 2023. The sharpest increase occurred in 2021, with nearly 18 ppb added—84 percent more than in 2019.
A key factor was the temporary decline in hydroxyl radicals, the atmosphere's primary methane-destroying agents. This slowdown, which explained about 80 percent of the year-to-year variability in methane buildup, stemmed largely from reduced nitrogen oxides during COVID-19 lockdowns, altering air pollution patterns. Concurrently, a prolonged La Niña phase from 2020 to 2023 created unusually wet conditions in the tropics, expanding flooded areas conducive to methane-producing microbes.
Emissions rose notably from wetlands, rivers, lakes, reservoirs, and paddy rice fields, particularly in tropical Africa and Southeast Asia. Arctic regions also saw increases due to warmer temperatures enhancing microbial activity, while South American wetlands experienced a decline in 2023 amid an El Niño-induced drought. Fossil fuel use and wildfires contributed minimally, with microbial sources dominating the surge.
"As the planet becomes warmer and wetter, methane emissions from wetlands, inland waters, and paddy rice systems will increasingly shape near-term climate change," Tian noted. Lead author Philippe Ciais of the University of Versailles Saint-Quentin-en-Yvelines added, "Future methane trends will depend not only on emission controls, but on climate-driven changes in natural and managed methane sources."
The study highlights gaps in current models for predicting emissions from flooded ecosystems, emphasizing the need for better monitoring to meet global methane reduction pledges.