West LA Times

The 2022 eruption of Hunga Tonga-Hunga Haʻapai, an underwater volcano, has resulted in unexpected cooling of the Southern Hemisphere, according to a study led by UCLA scientists. Originally, experts believed the eruption would contribute to global warming due to the anticipated release of water vapor into the stratosphere. However, the study found that temperatures over the Southern Hemisphere actually decreased by 0.1 degrees Celsius.

The eruption released less sulfur dioxide and more water vapor than anticipated. This combination led to smaller sulfate aerosols, which had a cooling effect stronger than the warming effect of water vapor. The water vapor interacted with other atmospheric components, like sulfur dioxide and ozone, without amplifying warming.

Ashok Gupta, an atmospheric scientist from UCLA, explained the implications for geoengineering — a method of combating climate change by introducing substances into the atmosphere that reflect solar radiation. He noted, "If we plan to use approaches that involve releasing sulfate aerosols into the stratosphere to reflect sunlight, we have to consider how other factors — such as water vapor and atmospheric mixing — could change the outcome."

The volcanic eruption on January 15, 2022, sent significant volumes of water vapor and moderate amounts of sulfur dioxide 200 meters above the ocean surface into the stratosphere, creating sulfate aerosols that reflected sunlight, contributing to cooling. This cooling was observed despite water vapor typically warming Earth’s surface when present at high altitudes.

The research, carried out in collaboration with Vanderbilt University and Pennsylvania State University scientists, used satellite data to track the atmospheric dispersion of volcanic emissions. The analysis revealed that the eruption's emissions caused radiative energy losses, resulting in cooling at different atmospheric levels. The findings are notable as they demonstrate the complex atmospheric changes that can occur following a shallow undersea volcanic eruption, emphasizing the importance of thorough understanding before geoengineering interventions.

Funding for the research was provided by NASA, the National Science Foundation, and the Simons Foundation. Gupta concluded that although the cooling effect was minor, "sulfate aerosols did indeed contribute to temporary cooling in the Southern Hemisphere." He emphasized the complexity of atmospheric interactions and the potential unforeseen consequences of geoengineering efforts.