The explosive eruption of the underwater volcano Hunga Tonga-Hunga Ha’apai in January 2022 injected at least 50 million metric tons of water vapor directly into the stratosphere, potentially increasing the amount of global stratospheric water vapor by more than 5%, according to a new study. The findings suggest that this event has likely initiated an atmospheric response different from that of previous well-studied large volcanic eruptions. Although rare, large volcanic eruptions can eject large amounts of gasses, ash and other particulates high into the atmosphere, where they can influence stratospheric chemistry and dynamics for several years following eruption. In addition to ash, sulfur-containing gasses are often considered the most important gases injected into the stratosphere and can result in a decrease in global climate temperature and accelerated ozone destruction. While it is thought that direct injection of water vapor could help moderate the climate impacts of volcanic aerosols, volcanic eruptions are generally not considered to be a major source for stratospheric water vapor. Even the largest eruptions over the past century have only resulted in minor water vapor injections. According to Holger Vömel and colleagues, however, the hydromagmatic eruption of Hunga Tonga-Hunga Ha’apai was quite different. Using in situ measurements from radiosondes carried aloft by high-altitude weather balloons, Vömel et al. show that this event injected a massive amount – at least 50 teragrams – of water vapor directly into the stratosphere, potentially increasing stratospheric water vapor by at least 5% on a global average. While the atmospheric impacts of this observationally unprecedented event remain uncertain, the authors suggest that the increased amounts of stratospheric water vapor could contribute to stratospheric cooling and surface warming over the months to come, and that these effects could persist longer than those caused by injected aerosols, which tend to drop out of the stratosphere through gravitational settling.
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