NEW YORK — When an undersea volcano erupted in Tonga in January, its watery explosion was huge and unusual — and scientists are still trying to understand its impacts.
The volcano, known as Hunga Tonga-Hunga Ha’apai, spewed millions of tons of water vapor into the atmosphere, according to a study published Thursday in the journal Science.
Researchers estimate that the eruption increased the amount of water in the stratosphere – the second layer of the atmosphere, above the range where humans live and breathe – by around 5%.
Now scientists are trying to figure out how all that water might affect the atmosphere and whether it might warm the Earth’s surface over the next few years.
“It was a once-in-a-lifetime event,” said lead author Holger Voemel, a scientist at the National Center for Atmospheric Research in Colorado.
Large eruptions usually cool the planet. Most volcanoes emit large amounts of sulfur, which blocks the sun’s rays, said Matthew Toohey, a climate researcher at the University of Saskatchewan who was not involved in the study.
The Tonga explosion was much more soggier: The eruption started under the ocean, so it threw up a plume with much more water than usual. And since water vapor acts as a heat-trapping greenhouse gas, the eruption will likely raise temperatures instead of lower them, Toohey said.
It’s unclear how much warming might be in store.
Karen Rosenlof, a climatologist with the National Oceanic and Atmospheric Administration who was not involved in the study, said she expects the effects to be minimal and temporary.
“This increase could slightly warm the surface for a short time,” Rosenlof said in an email.
The water vapor will stay in the upper atmosphere for a few years before entering the lower atmosphere, Toohey said. Meanwhile, the extra water could also accelerate the loss of ozone from the atmosphere, Rosenlof added.
But it’s hard for scientists to say for sure, because they’ve never seen an eruption like this.
The stratosphere extends from about 7.5 miles to 31 miles above Earth and is generally very dry, Voemel explained.
Voemel’s team estimated the volcano’s plume using an array of instruments suspended from weather balloons. Usually these tools can’t even measure water levels in the stratosphere because the amounts are so small, Voemel said.
Another research group monitored the explosion using an instrument on a NASA satellite. In their study, published earlier this summer, they estimated the eruption to be even larger, adding about 150 million metric tons of water vapor to the stratosphere, three times more than Voemel’s study.
Voemel acknowledged that satellite imagery could have observed parts of the plume that the balloon’s instruments could not capture, making his estimate higher.
Either way, he said, the Tonga explosion was unlike anything seen in recent history, and studying its aftermath could yield new insights into our atmosphere. .
