Cleaner Air During Pandemic Lockdowns Triggered Record Methane Surge, Study Finds
In a striking environmental paradox, the dramatic reduction in air pollution during global Covid-19 lockdowns actually fueled an unprecedented surge in atmospheric methane levels during the early 2020s, according to groundbreaking research published in the journal Science on Thursday. The study reveals that cleaner air inadvertently weakened Earth's natural atmospheric cleaning mechanisms, allowing this powerful greenhouse gas to accumulate at record rates.
The Methane Cleaning Mechanism Disrupted
Methane, which ranks as the second-largest contributor to climate change after carbon dioxide, is typically scrubbed from the atmosphere by hydroxyl radicals (OH) – short-lived molecules that act as nature's cleaning agents. These radicals are produced through chemical reactions involving nitrogen oxide emissions from human activities like transportation and industrial processes.
"It seems paradoxical: We pollute less but it's not good for methane levels," said Philippe Ciais, the study's lead author and associate director at the Laboratory of Climate and Environment Sciences near Paris. "These drops in OH are partly linked to the fact that we emitted less nitrogen oxide."
When pandemic restrictions dramatically reduced travel and shut down businesses worldwide, nitrogen oxide emissions plummeted. This decline in a key ingredient for hydroxyl radical production meant Earth's natural methane-cleaning capacity weakened significantly during 2020 and 2021.
Record Methane Acceleration and Contributing Factors
The research found that the sharp reduction in hydroxyl radicals explains approximately 80 percent of the annual variation in methane accumulation during the pandemic period. Methane levels had been rising steadily since 2007, but their growth accelerated dramatically during the lockdowns, peaking at 16.2 parts per billion per year in 2020 before declining by half by 2023.
"The impressive increase in methane in the air at the beginning of the 2020s is mainly due to a reduction in the oxidizing capacity of the atmosphere," Ciais emphasized during a press briefing.
The study identified additional contributing factors to the methane surge:
- Exceptionally wet conditions due to the cooling La Nina weather phenomenon between 2020 and 2023
- Increased methane emissions from wetlands, lakes, rivers, and agriculture in tropical regions
- Wetter-than-average conditions in tropical Africa and Southeast Asia that enhanced natural methane sources
Climate Implications and Policy Challenges
This unexpected finding raises critical questions about how clean air policies and pollution reduction efforts for vehicles, aircraft, and ships might inadvertently affect climate dynamics. Methane remains in the atmosphere for a much shorter time than carbon dioxide, but its warming effect is approximately 80 times more potent over a 20-year period.
"For me, this means we need to improve air quality and, even more importantly, mitigate greenhouse gas emissions, to offset these negative effects linked to the chemical-climate relationship," said study co-author Marielle Saunois, describing the phenomenon as "collateral damage" from reduced pollution.
Approximately 40 percent of methane emissions originate from natural sources, primarily wetlands, while the remaining 60 percent stem from human activities including agriculture and energy production.
"As the planet becomes warmer and wetter, methane emissions from wetlands, inland waters, and paddy rice systems will increasingly shape near-term climate change," warned Boston College professor and study co-author Hanqin Tian.
Global Methane Reduction Efforts
The scientists stress that these complex atmospheric interactions must be better understood and incorporated into global climate strategies. Their findings come as nearly 160 countries have committed to the Global Methane Pledge launched at COP26 in Glasgow in 2021, which aims to cut global methane emissions by 30 percent by 2030 compared to 2020 levels.
The research underscores the intricate balance between air quality improvement and climate protection, revealing that environmental solutions must address multiple interconnected systems simultaneously to avoid unintended consequences in our rapidly changing planetary system.
