When an undersea volcano erupted in 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, shot millions of tons of water vapor high up

into the atmosphere, according to a study published Thursday in the journal Science.

The researchers estimate 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 around 5%.

Now, scientists are trying to figure out how all that water could affect the atmosphere,

and whether it might warm 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.