Long-Term Climate Impacts of Large Stratospheric Water Vapor Perturbations

Abstract

Abstract The amount of water vapor injected into the stratosphere after the eruption of Hunga Tonga–Hunga Ha’apai (HTHH) was unprecedented, and it is therefore unclear what it might mean for surface climate. We use chemistry–climate model simulations to assess the long-term surface impacts of stratospheric water vapor (SWV) anomalies similar to those caused by HTHH but neglect the relatively minor aerosol loading from the eruption. The simulations show that the SWV anomalies lead to strong and persistent warming of Northern Hemisphere landmasses in boreal winter, and austral winter cooling over Australia, years after eruption, demonstrating that large SWV forcing can have surface impacts on a decadal time scale. We also emphasize that the surface response to SWV anomalies is more complex than simple warming due to greenhouse forcing and is influenced by factors such as regional circulation patterns and cloud feedbacks. Further research is needed to fully understand the multiyear effects of SWV anomalies and their relationship with climate phenomena like El Niño–Southern Oscillation. Significance Statement Volcanic eruptions typically cool Earth’s surface by releasing sulfur dioxide, which then converts into aerosols, which reflect sunlight. However, a recent eruption released a significant amount of water vapor—a strong greenhouse gas—into the stratosphere with unknown consequences. This study neglects the aerosol effect and examines the consequences of large stratospheric water vapor anomalies and reveals that surface temperatures across large regions of the world increase by over 1.5°C for several years, although some areas experience cooling close to 1°C. Additionally, the research suggests a potential connection between the eruption and sea surface temperatures in the tropical Pacific, which warrants further investigation.