When an undersea volcano in Tonga erupted in January, its watery eruption was massive and unusual — and scientists are still trying to understand its effects.
A study published Thursday in the journal Science reports that the volcano, known as Henga Tonga Hong Hapai, released millions of tons of water vapor high into the atmosphere.
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%.
Now, scientists are trying to figure out how all this water might affect the atmosphere, and whether it will warm the Earth’s surface over the next few 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.
Big eruptions usually cool the planet. Most volcanoes send out large amounts of sulfur, which blocks the sun’s rays, explained Matthew Toohy, a climate researcher at the University of Saskatchewan who was not involved in the study.
The explosion in Tonga was much stronger: The eruption began under the ocean, raising a column with much more water than usual. Because water vapor acts as a greenhouse gas that traps heat, it is likely that a volcanic eruption would raise temperatures rather than lower them, Tohey said.
It’s not clear how much warming that could hold.
Karen Rosenloff, climate world At the National Oceanic and Atmospheric Administration, which was not involved in the study, she said she expects the effects to be minimal and temporary.
“This amount of increase could warm the surface by a tiny amount for a short period of time,” Rosenloff said in an email.
The water vapor will remain around the upper atmosphere for a few years before making its way into the lower atmosphere, Tohey said. Meanwhile, Rosenloff added, the additional water may accelerate the loss of ozone in the atmosphere.
But it’s hard for scientists to say for sure, because they’ve never seen an eruption like this before.
Vojmel explained that the stratosphere extends from about 7.5 miles to 31 miles (12 km to 50 km) above the Earth and is usually very dry.
Voemel’s team estimated the volcano’s plume using a network of instruments suspended from weather balloons. These instruments usually can’t measure stratospheric water levels because the quantities are too low, Voemel said.
Another research group monitored the explosion with an instrument on a NASA satellite. In their study, published earlier this summer, they estimated that the eruption would be larger, adding about 150 million metric tons of water vapor to the stratosphere — three times what Voemel’s study found.
Voemel acknowledged that satellite imaging may have noticed parts of the column that balloon tools could not capture, making her estimate higher.
Either way, he said, the Tonga eruption was unlike anything seen in recent history, and studying its effects may hold new insights into our atmosphere.