PARIS: In a surprising twist of nature, lower air pollution during Covid lockdowns inadvertently contributed to a surge in methane, one of the planet’s most potent greenhouse gases, a new study revealed Thursday.
Research published in the journal Science found that methane levels rose at a record pace in the early 2020s as the gas’s main natural “cleaning agent” weakened during the pandemic.
The increase was also partly linked to higher emissions from wetlands, lakes, rivers, and agriculture, driven by wetter-than-average conditions in tropical regions, according to the study.
Methane is the second-largest contributor to climate change. Although it lingers in the atmosphere for a shorter time than carbon dioxide, its warming effect is roughly 80 times stronger over 20 years, according to AFP.
Natural hydroxyl radicals (OH) act as the atmosphere’s “cleaning agents,” breaking down methane over time, but they have a very short lifespan.
During Covid lockdowns, reduced travel and industrial activity led to a drop in nitrogen oxide, a key ingredient for producing hydroxyl radicals.
“These drops in OH are partly linked to the fact that we emitted less nitrogen oxide,” said Philippe Ciais, the study’s lead author and associate director at the Laboratory of Climate and Environment Sciences near Paris.
“It seems paradoxical: We pollute less, but it’s not necessarily good for methane levels,” Ciais added.
The sharp decline in hydroxyl radicals in 2020 and 2021 explained roughly 80 percent of the annual variation in methane accumulation, the research noted.
Methane had been rising steadily since 2007, but its growth accelerated during the pandemic, peaking at 16.2 parts per billion per year in 2020 before dropping by half by 2023.
“The impressive increase in methane in the early 2020s is mainly due to a reduction in the oxidizing capacity of the atmosphere,” Ciais said.
This paradox raises important questions about how to ensure that clean air policies, such as reducing emissions from cars, planes, and ships, do not unintentionally affect climate.
Marielle Saunois, a co-author, called it “collateral damage.” “For me, this shows we need to improve air quality and, even more importantly, mitigate greenhouse gas emissions to offset these chemical-climate effects,” she said.
The study also highlighted the role of exceptionally wet conditions caused by the La Nina weather phenomenon from 2020 to 2023, particularly in tropical Africa and Southeast Asia.
Around 40 percent of methane emissions come from natural sources, mainly wetlands, while the rest is largely due to human activities such as agriculture and energy production.
“As the planet becomes warmer and wetter, methane emissions from wetlands, inland waters, and paddy rice systems will increasingly influence near-term climate change,” said Hanqin Tian, a Boston College professor and co-author of the study.
Scientists stress that these complex interactions must be better understood and incorporated into global efforts to reduce methane emissions.
Under the Global Methane Pledge, launched at COP26 in Glasgow in 2021, nearly 160 countries have committed to cutting global methane emissions by 30 percent by 2030 compared with 2020 levels.
