In an unexpected outcome, the Covid-19 lockdowns, which reduced air pollution worldwide, were linked to a sharp rise in methane levels, a powerful greenhouse gas, according to a study published on Thursday in the journal Science.Researchers found that methane levels increased at a record pace in the early 2020s because the atmosphere’s natural “cleaning agents”, known as hydroxyl radicals (OH), weakened during that time. These molecules normally help break down methane and remove it from the atmosphere.During the lockdowns, travel dropped and many businesses shut down. This reduced emissions of nitrogen oxide, a key ingredient needed to produce hydroxyl radicals. As a result, fewer hydroxyl radicals were available to remove methane from the air.The study found that the drop in hydroxyl radicals in 2020 and 2021 explained about 80 percent of the yearly increase in methane levels. Methane had already been rising since 2007, but the increase accelerated during the pandemic. It reached a peak growth rate of 16.2 parts per billion per year in 2020 before slowing by about half by 2023.Methane is the second-largest contributor to climate change after carbon dioxide. Although it stays in the atmosphere for a shorter time, its warming effect is about 80 times stronger than carbon dioxide over a 20-year period.About 40 percent of methane emissions come from natural sources like wetlands, while the rest come from human activities such as agriculture and energy production. Nearly 160 countries have pledged under the Global Methane Pledge to cut methane emissions by 30 percent by 2030 compared with 2020 levels.