Atmospheric methane rose by about 55 parts per billion between 2019 and 2023, reaching a record 1,921 parts per billion, with the growth rate peaking in 2021. Explaining that surge matters because methane has more than eighty times the warming power of carbon dioxide over twenty years and accounts for roughly a third of current warming. A team led from the College of Urban and Environmental Sciences at Peking University combined satellite data, ground observations and models to identify the causes.
The dominant factor turned out to be removal rather than release. Hydroxyl radicals, the primary oxidant that strips methane from the atmosphere, declined sharply in 2020 and 2021, and this temporary weakening of the sink explains roughly 80 per cent of the year-to-year variability in methane growth from 2019 to 2023. Reduced nitrogen oxide emissions during the pandemic contributed to the lower hydroxyl levels, allowing methane to accumulate faster than emissions alone would predict.
Natural emissions played a secondary but real role. An extended La Nina event from 2020 to 2023 brought wetter conditions to tropical regions, and expanded wetlands and inland waters in tropical Africa and Southeast Asia, together with increased emissions from Arctic wetlands and lakes, boosted microbial methane production. Fossil fuel and wildfire emissions contributed only marginally. The study was published in Science.
The analytical implication is awkward for monitoring regimes built around emissions inventories. If a large share of observed methane variability originates in the atmosphere's oxidising capacity and in climate-driven natural sources, then concentration trends cannot be read directly as a verdict on mitigation policy. Attributing future trends will require tracking the sink with the same seriousness as the sources.