When an underwater volcanoin January, its watery explosion was huge and unusual – and scientists are still trying to understand its effects.
The volcano, known as Hunga Tonga-Hunga Ha’apai, has released millions of tons of water vapor into the atmosphere, according to a study published Thursday in the journal Science.
The researchers evaluate the eruption, whichraised the amount of water in the stratosphere – the second layer of the atmosphere, above the range in which humans live and breathe – by about 5%.
Now scientists are trying to figure out how all this water could affect the atmosphere and whether it could warm the Earth’s surface in the next few years.
“It was a once in a lifetime event,” said lead author Holger Womel, a scientist at the National Center for Atmospheric Research in Colorado.
Large eruptions usually cool the planet. Most volcanoes emit 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 explosion in Tonga was much wetter: the eruption began under the ocean, so it threw out a plume with much more water than usual. And because water vapor acts as a greenhouse gas that traps heat, the eruption is likely to raise temperatures rather than lower them, Toohey said.
It’s unclear how much warming might be in store.
Karen Rosenlof, a climate scientist with 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 may heat up the surface slightly for a short period of time,” Rosenlof said in an email.
In August, scientists said it had broken “every record” for injecting water vapor since satellites began recording such data – enough water vapor to fill.
Water vapor will stay in the upper atmosphere for several years before it enters the lower atmosphere, Toohey said. At the same time, 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 such an eruption.
The stratosphere extends from 7.5 to 31 miles above the Earth and is usually very dry, Womel said.
Vomel’s team assessed the plume of the volcano using a network of instruments suspended from weather balloons. Usually, these instruments can’t even measure the water level in the stratosphere because the amount of water is so small, Vomel said.
Another research team observed the explosion using an instrument on a NASA satellite. In their study, published earlier this summer, they calculated that the eruption was even larger, adding about 150 million metric tons of water vapor to the stratosphere – three times more than Voemel’s study showed.
In this study, the scientists also concluded that the unprecedented plume could temporarily affect the Earth’s global average temperature.
Vomel acknowledged that the satellite imagery could have shown parts of the plume that the balloon’s instruments could not pick up, boosting his estimate.
In any case, he said, the explosion in Tonga is unlike anything seen in recent history, and studying its aftermath could provide new insights into our atmosphere.