COVID lockdowns triggered record methane surge
Pandemic measures that emptied city streets and grounded airplanes inadvertently weakened the atmosphere's ability to clear methane, sparking the largest recorded jump in this potent greenhouse gas, according to a new study in Science.
A team of 41 scientists led by Peking University researchers found that reduced hydroxyl radicals from 2020 to 2021, followed by recovery through 2023, accounted for about 80% of year-to-year methane growth rate swings. Hydroxyl radicals, dubbed the atmosphere's "Pac-Man," normally oxidize methane produced by vehicles, planes, and ships. Lockdowns slashed nitrogen oxide emissions, curtailing radical production and letting methane linger longer.
Peking University's Shushi Peng, a lead author, noted expectations of slight anthropogenic methane drops during restrictions. NOAA data shows 2020's annual methane growth hit 15 parts per billion, the highest since systematic records began in 1983, then shattered again at 17.7 ppb in 2021. Global emissions rose from roughly 550 teragrams in 2010-2019 to 570-590 teragrams in 2020-2022.
Tropical wetland expansion fueled the spike alongside atmospheric shifts. Three straight La Niña years brought heavy rains, swelling equatorial Asia and Africa wetlands, which contributed 43% and 30% of excess atmospheric methane per separate PNAS studies. Waterlogged soils host microbes that generate methane decomposing organic matter anaerobically. Warmer, wetter conditions proved ideal for these producers.
The findings pose policy dilemmas. Cleaner air benefits public health but may inadvertently hasten methane buildup. "As air cleans up, we lose methane sinks in the atmosphere," Peng explained. "Thus we must cut anthropogenic emissions harder." UC Riverside climatologist Francesca Hopkins, not involved, warned fossil fuel cuts could briefly amplify warming via OH chemistry effects, though combustion reductions remain vital for climate limits. Accompanying commentary by Euan Nisbet and Martin Manning highlighted methane capture potential from China's and India's coal mines, landfills, and wastewater plants.
