When an undersea volcano erupted in Tonga in January, its blast of water was huge and unusual – and scientists are still trying to understand the effects.
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 area where humans live and breathe – by around 5%.
Now scientists are trying to find out how all that water might affect the atmosphere, and whether it might warm the Earth’s surface over the next few years.
“This was a once-in-a-lifetime event,” said lead author Holger Voemel, a researcher at the National Center for Atmospheric Research in Colorado.
Large eruptions usually cool the planet. Most volcanoes emit large amounts of sulphur, which blocks the sun’s rays, explained Matthew Toohey, a climate scientist at the University of Saskatchewan who was not involved in the study.
The Tongan explosion was much wetter: The eruption started under the sea, so it shot up a cloud with much more water than usual. And since water vapor acts as a heat-trapping greenhouse gas, the eruption is likely to raise temperatures rather than lower them, Toohey said.
It is unclear how much warming can be expected.
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 increase can warm the surface a small amount for a short period of time,” Rosenlof said in an email.
The water vapor will stay around the upper atmosphere for a few years before entering the lower atmosphere, Toohey said. Meanwhile, the extra water could also speed up ozone loss 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 usually 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 team 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 tons of water vapor to the stratosphere — three times as much as Voemel’s study found.
Voemel acknowledged that the satellite imagery may have observed parts of the cloud that the balloon instruments could not capture, making the estimate higher.
Regardless, he said, the Tongan explosion was unlike anything seen in recent history, and studying the aftermath could provide new insights into our atmosphere.
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