New Delhi: Scientists have unraveled a climate puzzle that baffled researchers around the world: despite the dramatic reductions in pollution during the COVID-19 pandemic lockdowns, atmospheric methane one of the planet’s most potent greenhouse gases surged to record levels between 2020 and 2022. A landmark international study published in Science explains that this unexpected rise was driven not by increased emissions alone, but by a temporary shift in atmospheric chemistry and natural climate factors.
When countries across the globe-imposed lockdowns to curb the spread of COVID-19, economic and transportation activities came to a near halt. Roads emptied, factories shut down, and air travel plummeted. While this led to noticeable short-term improvements in air quality, scientists were surprised to observe that atmospheric methane concentrations grew at the fastest rate ever recorded during the early 2020s. Methane is a powerful greenhouse gas more than 25 times as effective as carbon dioxide at trapping heat over a 100-year period and its rise counteracted some climate benefits expected from reduced carbon emissions during the pandemic.
The new research shows that the key to this paradox was a significant decline in hydroxyl radicals (OH) highly reactive molecules in the atmosphere often referred to as its “detergent”. Under normal conditions, these radicals react with methane, breaking it down and preventing it from lingering in the air. However, during 2020 and 2021, levels of OH dropped sharply.
The drop in hydroxyl radicals was linked to reduced emissions of nitrogen oxides (NOₓ) and other pollutants from vehicles and industrial sources, which are essential for the formation of OH. With fewer of these precursors in the atmosphere a consequence of lockdown-related declines in human activity the atmosphere’s ability to remove methane slowed significantly. According to the study, this weakened removal process explains roughly 80–85% of the year-to-year variability in methane growth during that period.
In addition to changes in atmospheric chemistry, the study found that natural climatic conditions amplified the methane surge. From 2020 to 2023, an extended La Niña phase brought wetter-than-average conditions to large areas of the tropics. These wetter conditions expanded wetlands environments rich in microbial life that produce methane as they break down organic material without oxygen. Enhanced methane emissions from wetlands, inland waters, and agricultural landscapes contributed further to rising atmospheric methane levels.
The findings emphasize that methane dynamics are governed by a complex interplay of human activity, atmospheric chemistry, and natural environmental processes. While fossil fuel leaks, agriculture, and waste management are known methane sources, the pandemic period demonstrated that changes in how the atmosphere reacts to emissions can have equally significant impacts.
Scientists involved in the research pointed out that the surge highlights an important climate insight: reducing air pollutants can sometimes lead to less production of atmospheric cleaning agents like hydroxyl radicals, inadvertently allowing long-lived greenhouse gases like methane to accumulate. This underscores the need for integrated climate strategies that consider both emissions and atmospheric reactions.
By reconstructing the global methane budget through 2023, the study provides valuable context for understanding how greenhouse gases behave under rapidly changing environmental conditions. It highlights the indispensable role of satellite observations and sophisticated models in monitoring atmospheric composition and improving climate projections.
The research ultimately offers a nuanced perspective on the relationship between air quality improvements and climate change, reminding policymakers and scientists alike that achieving long-term climate stability requires a deeper understanding of both emissions and atmospheric feedbacks.