The reduction in pollution during the COVID-19 lockdown has caused significant chemical changes in the atmosphere, leading to a concerning rise in methane concentrations that could greatly affect future climate change.

Methane, which remains in the atmosphere for only about a decade, has a much higher warming potential than CO2. Its levels have been rising since the 1980s, mainly due to emissions from fossil fuel production. In recent decades, increased microorganisms breaking down organic matter in wetlands, agriculture, and landfills have further amplified these emissions.

From 2020 to 2022, the atmospheric methane surge unexpectedly doubled from approximately 20 million tons per year to roughly 40 million tons annually, reverting to about 20 million tons in 2023. A recent study indicates that this spike is largely attributed to a reduction in nitrogen oxide (NOx) emissions from vehicles, aviation, and shipping during the lockdown.

NOx compounds catalyze atmospheric reactions that produce hydroxyl radicals (OH), key for breaking down methane. Hence, a decline in NOx typically results in enhanced methane persistence.

According to Matthew Johnson from the University of Copenhagen, “Reducing catalyst emissions leads to an increased methane pollution, akin to a hangover from our fossil fuel dependency.”

Prior research by Professors at Peking University indicated that the methane spike in 2020 was largely due to a decline in hydroxyl radicals and an increase in emissions from wetlands. Surprisingly, methane growth rates continued to rise in 2021 and 2022, despite the global economy’s recovery.

While hydroxyl radicals are too short-lived for direct measurement, satellite data can detect the gases that produce them. The recent study modeled both terrestrial methane sources and atmospheric hydroxyl radical sinks, linking their data with measured methane concentrations.

It discovered that the decline in hydroxyl radicals during 2020-21 and their recovery in 2022-23 accounted for 83% of the variations in methane growth rates. Continued low aviation emissions in 2021, coupled with the slow recovery of the transportation sector, contributed to these findings.

The increase in methane emissions from wetlands and inland waters accounted for the remaining spike. The La Niña climate phase boosted precipitation in Central Africa, expanding wetlands and generating more methane. Additionally, worsening weather in South and Southeast Asia increased methane emissions from rice fields, while rising temperatures accelerated methane emissions from Arctic wetlands.

As countries like China and India move toward electrification, the reduction in NOx pollution could further escalate methane growth, warns Penn.

“Improved air quality will likely mean decreasing methane absorption in the atmosphere,” he states, underscoring the urgent need for reducing human-caused emissions.

Disparities exist within climate models; some predict a decline in hydroxyl radicals, while others foresee an increase. Difficulties in measuring hydroxyl concentrations may also cast uncertainty over this study’s results.

Echoing this sentiment, Paul Palmer from the University of Edinburgh expressed surprise at the significance of hydroxyl radical changes compared to emission fluctuations. “If validated, this findings necessitate a reevaluation of factors influencing hydroxyl radicals in the global troposphere.”

Attributing changes to hydroxyl radicals might underestimate the actual variations in methane emissions.

Regardless, methane emissions from wetlands are set to escalate due to global warming, increasing precipitation, and microbial activity. To mitigate climate change, urgent human intervention is essential.

The new research highlighted by Ewan Nisbet from Royal Holloway, University of London, and Martin Manning from Victoria University in Wellington emphasizes that nations like China and India have substantial opportunities to capture methane from coal mines, landfills, and wastewater treatment facilities. Global oil and gas production continues to lose significant amounts of methane as well.

“We need urgent action; the methane emissions situation is becoming increasingly critical,” Johnson concluded. “Current trends are reflecting the alarming increase in methane emissions driven by climate change.”