August 18th, 2025
Key Findings
- ENSO variability is driving tropospheric ozone and subsequently its radiative forcing through different mechanisms, including wildfires. For the first time, the contribution of these different mechanisms is quantified.
- GFDL’s atmospheric model, AM4.1, effectively simulates El Niño-Southern Oscillation-driven tropospheric ozone anomalies compared to satellite retrievals
- This study shows that tropospheric ozone’s radiative effects strengthen during La Niña and weaken during El Niño.
- The authors identified the dominant drivers of these changes: biomass burning plays the largest role over equatorial Asia, lightning dominates over oceans, and stratospheric intrusion has the strongest impact near the subtropics.
Arman Pouyaei, Paul Ginoux, Vaishali Naik, Jing Feng, Larry W. Horowitz, Fabien Paulot. Geophysical Research Letters. DOI: 10.1029/2025GL115898
Ozone is a powerful greenhouse gas that efficiently traps heat, especially in the tropical upper troposphere. In this study, the authors used GFDL’s Atmospheric Model v4.1 (AM4.1) to investigate how the El Niño-Southern Oscillation (ENSO) influences three key processes affecting ozone: biomass burning, lightning-produced nitrogen oxides, and stratospheric ozone intrusion. These findings show that tropospheric ozone’s radiative effects strengthen during La Niña and weaken during El Niño.
The authors identified the dominant drivers of these changes: biomass burning plays the largest role over equatorial Asia, lightning dominates over oceans, and stratospheric intrusion has the strongest impact near the subtropics. These results highlight the importance of understanding ENSO-driven ozone radiative forcing variability for improving our interpretation of climate variability and its potential impacts.
This study demonstrates that AM4.1, incorporating both tropospheric and stratospheric chemistry, accurately simulates observed ENSO-driven tropospheric ozone anomalies compared to satellite retrievals, making it suitable for assessing global ozone profiles and tropospheric ozone radiative forcing. The model includes detailed ozone chemistry dynamically coupled to the model, allowing ENSO-related changes to influence emissions and subsequent ozone chemistry and radiative forcing. This study focused on ENSO events from 2004 to 2019, covering a range of weak to moderate/strong phases. This period offers high-quality observational and emissions data, but it does not capture the full diversity of ENSO behavior. In a changing climate, the strength of ENSO will change, thus more natural emissions, and/or changes in STE will affect tropospheric ozone radiative forcing.
These past few years have witnessed a surge in wildfire intensity and frequency in some areas, associated with drought and ENSO variability. This work allows us to better understand these links and how it further affects ozone radiative forcing.
