Distinct anthropogenic aerosol and greenhouse gas effects on El Niño/Southern Oscillation variability
El Niño-Southern Oscillation (ENSO) is a natural climate phenomenon involving periodic variations in sea surface temperatures and atmospheric pressure across the tropical Pacific, having significant global weather and climate impacts. It can trigger heavy rainfall in South America and severe droughts in Australia. Currently, Southern California is battling devastating wildfires, a disaster closely linked to the La Niña event that start in the beginning of 2025. Over the past few decades, human activities have profoundly altered the behavior of ENSO. Emissions of anthropogenic aerosols and greenhouse gases are reshaping this climate phenomenon in distinct ways. Understanding these changes is not only important for advancing scientific knowledge but also helpful for predicting future climate risks and developing effective mitigation strategies. This forms the scientific question of our research: investigating how anthropogenic aerosols and greenhouse gases influence ENSO variability.
Our research focuses on the distinct impacts of anthropogenic aerosols and greenhouse gases on ENSO variability. We analyzed the feedback mechanism and dynamic behavior of the ENSO using a broad set of climate model in combination with historical and single-forcing experiments (forced only by historical anthropogenic aerosols or well-mixed greenhouse gases). Our findings reveal that anthropogenic aerosols amplify ENSO variability by weakening the annual cycle of sea surface temperatures in the tropical Pacific and enhancing positive feedback. In contrast, greenhouse gases suppress ENSO variability by strengthening the annual cycle of sea surface temperature, which constrains ENSO’s natural oscillations. Between 1850 and 2014, emissions of both aerosols and greenhouse gases rose dramatically, and their opposing impacts on ENSO variability likely offset each other to some extent. However, looking ahead, aerosol emissions are expected to peak in the early twenty-first century and then gradually decline, while greenhouse gas concentrations will continue to rise. This shift will redefine their combined influence on ENSO, determining whether their effects will persist in offsetting each other or potentially interact synergistically in certain aspects.
These findings highlight the complex response of ENSO to different climate forcings and highlight the interactions between natural climate variability and anthropogenic drivers. This is not only key to understanding the possible trajectory of future ENSO variability, but also has implications for exploring potential changes in the driving mechanism of surface warming patterns in the tropical Pacific. Our findings provide an important scientific basis for studying the behavior of ENSO in the context of future climate change, while also reminding us to pay more attention to the long-term combined effects of anthropogenic forcings on the climate system.
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Communications Earth & Environment
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