NEW YORK — When a submarine volcano erupted in Tonga in January, the watery explosion was huge and unusual — and scientists are still trying to understand its impact.
The volcano, known as Hunga Tonga-Hunga Ha’apai, shot millions of tons of water vapor high into the atmosphere, according to a study published Thursday in the journal Science.
The 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 about 5 percent.
Now scientists are trying to figure out how all that water could affect the atmosphere and whether it could warm the Earth’s surface in the coming years.
“This 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, explains Matthew Toohey, a climate researcher at the University of Saskatchewan who was not involved in the study.
The Tongan explosion was much more humid: The eruption started under the ocean, so it shot up a plume with much more water than usual. And since water vapor acts as a greenhouse gas that traps heat, the eruption will likely raise the temperature rather than lower it, Toohey said.
It’s unclear how much warming may be in store.
Karen Rosenlof, a climate scientist 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 amount of increase can warm up the surface a small amount for a short period of time,” Rosenlof said in an email.
The water vapor will linger around the upper atmosphere for a few years before making its way to the lower atmosphere, Toohey said. In the meantime, the extra water could also accelerate ozone loss into 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 12 miles to 50 miles above Earth and is usually very dry, Voemel explained.
Voemel’s team estimated the volcanic plume using a network of instruments suspended from weather balloons. Most of the time, these tools can’t even measure water levels in the stratosphere because the amounts are so low, Voemel said.
Another research group tracked the explosion with an instrument on a NASA satellite. In their study, published earlier this summer, they estimated the eruption would be even bigger, adding about 150 million tons of water vapor to the stratosphere — three times as much as Voemel’s study showed.
Voemel acknowledged that the satellite images may have spotted parts of the plume that the balloon instruments were unable to capture, raising the estimate.
Either way, he said, the Tongan explosion was unlike anything seen in recent history, and studying its aftermath could provide new insights into our atmosphere.