2021 Volcano Eruption Impacted Earth’s Atmosphere for 2 Years: Study

When the underwater Hunga Tonga volcano erupted in the South Pacific, it blasted an “unprecedented” amount of aerosols and water vapor into Earth’s atmosphere. Now, scientists are saying the plume was significant enough to affect atmospheric temperature, circulation patterns, and radiative balance for two years after the explosion ended. 

Hunga Tonga kicked off the largest underwater explosion recorded by modern science on Dec. 20, 2021. For days, the submarine volcano released sulfur dioxide, ash, and steam several miles into the air. On Jan. 14, 2022, the event culminated in a massive eruption heard in Fiji (430 miles away) and Samoa (520 miles away). This final eruption ejected stone, ash, and water vapor roughly 12 miles into the atmosphere. 

A few months later, an analysis by NASA atmospheric scientist Luis Millán revealed that Hunga Tonga had blown 146 teragrams (146 trillion grams) of water into the atmosphere—enough water to fill an Olympic swimming pool 58,000 times over. The plumes increased the amount of water in Earth’s atmosphere by 10%, causing some researchers to worry that the extra moisture would exacerbate the greenhouse effect. Today, we know that Hunga Tonga’s alarming ejections not only altered Earth’s normal atmospheric processes but did so for years—just not in a way most scientists expected.

Credit: Japan Meteorological Agency/NASA SPoRT/Wikimedia Commons

In a paper for JGR Atmospheres, researchers in the United States and Canada write that while Hunga Tonga’s aerosols and water vapors dispersed gradually throughout 2022 and 2023, they triggered changes in the atmosphere’s ability to manage temperature and solar radiation. Thankfully, the volcanic aerosols that accumulated were better at reflecting sunlight into space than water vapor at trapping heat in the atmosphere. This means that the 10% moisture boost mentioned earlier didn’t contribute to atmospheric warming; during March and April 2022, the tropical stratosphere was cooler (by about 4 degrees Celsius) than it normally is at that time of the year. By 2023, most of the aerosols and water vapor had dissipated, bringing the atmosphere closer to its pre-Hunga Tonga eruption state.

But by releasing up to 1.5 metric megatons of sulfur dioxide into the air, Hunga Tonga created an abundance of sulfate aerosols in the atmosphere. These aerosols reflect sunlight, ultimately creating a gap in radiative forcing, or the trade-off between outgoing radiation from Earth and incoming radiation from the Sun. Thankfully, the scientists note that Hunga Tonga’s sulfate aerosols only briefly affected Earth’s radiative balance. While Earth typically absorbs an average of 240 watts of solar power per square meter every year, the aerosols triggered a 0.25-watt decrease in radiative flux in the two years following the volcano’s eruption.

“By the end of 2023, most of the Hunga induced radiative forcing changes [had] disappeared,” the researchers write.