When an undersea volcano erupted off Tonga in January, its watery blast was huge and unusual, and scientists are still trying to understand its impacts.
The volcano, known as Hunga Tonga-Hunga Ha’apai, released millions of tons of water vapor into the atmosphere, according to a study published Thursday in the journal Science.
The researchers estimate that the eruption raised the amount of water in the stratosphere, the second layer of the atmosphere, above the range where humans live and breathe, by about 5%.
Now scientists are trying to figure out how all that water could affect the atmosphere and whether it could warm 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 often cool the planet. Most volcanoes spew out large amounts of sulfur, 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 Tonga blast was much more soggy: The eruption started under the ocean, so it shot out 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 rather than lower them, Toohey said.
It’s unclear how much warming there might 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 minimal and temporary.
“This amount of increase could warm the surface by a small amount over a short period of time,” Rosenlof said in an email.
The water vapor will stay in the upper atmosphere for a few years before reaching the lower atmosphere, Toohey said. Meanwhile, the additional water could also accelerate 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 (12 km to 50 km) above Earth and is typically very dry, Voemel explained.
Voemel’s team estimated the volcano’s plume using a network of instruments suspended from weather balloons. Typically, these tools can’t even measure water levels in the stratosphere because the amounts are so low, 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 was even larger, adding about 150 million metric tons of water vapor to the stratosphere, three times more than Voemel’s study found.
Voemel acknowledged that satellite images might have seen parts of the column that the balloon’s instruments couldn’t, raising his estimate higher.
Either way, he said, the Tonga explosion is unlike anything seen in recent history, and studying its aftermath may provide new insights into our atmosphere.
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