In recent years, the atmospheric concentration of methane (CH₄) has experienced unprecedented fluctuations, with an especially sharp surge observed between 2020 and 2021. This increase, which reached a staggering 16.2 parts per billion per year (ppb yr⁻¹), marked the fastest growth rate ever recorded, before subsequently declining to 8.6 ppb yr⁻¹ by 2023. Methane is recognized as one of the most potent greenhouse gases, with a global warming potential many times greater than carbon dioxide over a 20-year horizon. Understanding the drivers behind such dramatic atmospheric changes in methane levels is imperative for refining climate models and informing mitigation strategies.
Central to recent scientific investigations has been the puzzling observation that methane concentrations did not simply rise due to increased emissions but rather resulted from a complex interplay between emission sources and the atmosphere’s chemical capacity to remove methane. The key atmospheric component responsible for breaking down methane is the hydroxyl radical (OH), often referred to as the “atmosphere’s detergent.” OH radicals react with methane, initiating its oxidation and thus reducing its atmospheric lifetime.
During the early 2020s, a notable decrease in atmospheric OH radicals was detected, suggesting a diminished oxidative capacity. This decreased availability of OH radicals effectively slowed methane removal, allowing CH₄ to accumulate more rapidly in the atmosphere. Conversely, from 2022 onward, OH levels began to recover, coinciding with a deceleration in methane’s atmospheric growth rate.
A critical complication for researchers examining this phenomenon lay in teasing apart the relative roles of emission changes versus shifts in atmospheric chemical processing, especially because the early 2020s coincided with the global COVID-19 pandemic. The pandemic induced widespread reductions in anthropogenic emissions, including those of OH precursors. Such reductions could theoretically have influenced hydroxyl radical concentration, adding layers of complexity to methane budget analyses.
To confront these challenges, a multidisciplinary team led by Philippe Ciais employed an integrative approach combining atmospheric chemical transport models with extensive bottom-up emission inventories. These inventories comprehensively accounted for various methane sources, ranging from anthropogenic activities like fossil fuel extraction and agriculture to natural sources such as wetlands and inland waters. By fusing these datasets, the team sought to refine the global and regional methane budget covering 2019 to 2023.
Their analysis revealed that fluctuations in atmospheric OH radical concentrations dominated methane growth rate variations during this period. Approximately 80% of the observed year-to-year changes in methane growth could be attributed to changes in the atmosphere’s oxidative capacity rather than emission fluctuations alone. This insight challenges conventional assumptions that primarily emphasize emission increases as the sole driver of methane surges.
Notwithstanding the predominant role of OH variability, the remaining 20% of methane growth was linked to emission increases, particularly from tropical wetlands in Africa, Asia, and the Arctic. These wetland regions are known hotspots for methane release, driven by complex biogeochemical processes sensitive to hydrological and climatic conditions. The confluence of a temporary weakening in methane destruction alongside enhanced emissions from these regions produced the unique atmospheric signal observed during the early 2020s.
The importance of tropical wetlands in atmospheric methane budgets cannot be overstated. Wetlands act as both sources and sinks in the methane cycle, with emissions strongly influenced by temperature, water table depth, and microbial activity. The observed increase in methane emissions from these areas during the 2020-2021 interval underscores the sensitivity of natural methane sources to environmental variability and climate change influences.
Importantly, the findings presented by Ciais et al. underscore atmospheric chemistry as a dynamic component of the methane budget, susceptible to rapid fluctuations driven by anthropogenic and natural factors alike. The interplay between emissions and chemical sinks complicates efforts to predict methane trends, revealing a need for more integrated observational networks and modeling frameworks that capture both emission and chemical transformation processes in real time.
The COVID-19 pandemic period represented an unexpected natural experiment, enabling scientists to observe how disruptions in anthropogenic activities trickle through atmospheric chemistry. Reduced industrial emissions likely contributed to transient OH radical changes, thus altering methane’s atmospheric lifetime. This ephemeral chemical response illustrates the tightly coupled nature of human activities, atmospheric chemistry, and greenhouse gas dynamics.
As the atmosphere continues to evolve under mounting anthropogenic pressures, understanding the mechanisms controlling methane concentrations remains a high priority. The work of Ciais and colleagues provides critical evidence that focusing solely on emission reductions, while essential, may overlook key dynamics related to the atmospheric destruction capacity. Enhanced monitoring of OH radical concentrations, along with detailed characterization of methane source variability, will be pivotal in constructing effective methane mitigation strategies.
These insights also carry broader implications for climate policy. By clarifying that atmospheric chemistry substantially influences methane abundance, climate models can be refined to better represent feedbacks and nonlinearities in methane cycling. This is crucial for establishing emission targets that realistically reflect the complex drivers of atmospheric methane and for anticipating future climate trajectories with greater confidence.
In conclusion, the extraordinary methane surge of the early 2020s emerged from a synergistic effect of both weaker atmospheric removal processes and heightened natural emissions. The findings illuminate the nuanced mechanisms behind greenhouse gas fluctuations, reminding us of the atmosphere’s intricate chemical ballet. As global methane monitoring intensifies, such knowledge will be indispensable for halting methane’s warming influence and safeguarding planetary health.
Subject of Research: Atmospheric methane dynamics during the early 2020s, focusing on the roles of oxidizing capacity and wetland emissions.
Article Title: Why methane surged in the atmosphere during the early 2020s
News Publication Date: 5-Feb-2026
Web References: http://dx.doi.org/10.1126/science.adx8262
Keywords: Methane, atmospheric chemistry, hydroxyl radicals, greenhouse gas, wetland emissions, methane budget, atmospheric oxidizing capacity, COVID-19 impact, climate change, methane growth rate, tropical wetlands, atmospheric modeling
