NEW YORK – When an undersea volcano erupted in Tonga in January, its watery blast was huge and unusual – and scientists are still trying to understand its impact.
The volcano, known as Hunga Tonga-Hunga Ha’apai, spewed millions of tons of water vapor high into the atmosphere, according to a study published Thursday in the journal Science.
Researchers estimate that the amount of water in the stratosphere — the second layer of the atmosphere, above the space where people live and breathe — will drop by about 5 percent.
Now, scientists are trying to describe how all that water might affect the atmosphere, and whether the Earth’s surface might warm up in the next few years.
“This was a once-in-a-lifetime event,” said lead author Holger Voemel, a scientist at the National Atmospheric Center in Colorado.
Large eruptions tend to cool the planet. Most volcanoes emit large amounts of sulphur, which blocks the sun’s rays, explained Matthew Toohey, a climate researcher at the University of Saskatchewan who was not involved in the study.
The Tongan eruption was much soggier: the eruption began under the ocean, so that the plume released much more water than usual. And since water vapor acts as a greenhouse gas-trapping gas, the eruption will likely raise temperatures instead of lowering them, Toohey said.
It is uncertain how hot it can be in store.
Karen Rosenlof, a climate scientist at the National Oceanic and Atmospheric Administration who was not involved in the study, said she expects the effects to be small and temporary.
“This amount of growth could support a small surface area in a short amount of time,” Rosenlof said in an email.
Water vapor will stick around the upper atmosphere for several years before making its way into the lower atmosphere, Toohey said. Meanwhile, extra water also accelerates the loss of ozone in 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 the driest, Voemel explained.
Voemel’s team assessed the volcano’s crest using a network of instruments suspended from weather balloons. Generally, these instruments can’t even measure water levels in the stratosphere because the levels are so low, Voemel said.
Another research group is using a NASA satellite instrument to monitor the explosion. In their study, published earlier this summer, they estimated that the eruption was larger, sending about 150 million metric tons of water vapor to the stratosphere — three times as much as Voemel’s study found.
Voemel acknowledged that satellite imaging could have observed parts of the ridge that the balloons’ instruments could not capture, making a higher estimate.
Either way, he says, the Tongan sound was unlike anything seen in recent history, and studying its reconstruction can hold new inspirations for our atmosphere.
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