The Hunga Tonga-Hunga Ha’apai eruption lasted less than a day, but it unleashed the most water vapor into the atmosphere by a volcano on record. Researchers say the blast may temporarily warm surface temperatures in years to come and also deplete stratospheric ozone.
NASA satellite data show the volcano launched more than 146 teragrams of water — enough to fill 58,000 Olympic-size swimming pools — to Earth’s second layer of the atmosphere, known as the stratosphere, where the ozone layer is located and just above where airplanes fly. The study stated the amount released is equivalent to 10 percent of the water already in the stratosphere.
“This is the first time that this type of injection happened in the entire satellite era,” which includes water vapor data back to 1995, said Luis Millán, lead study author and atmospheric scientist at NASA. “We have never seen anything like this before so that was quite impressive.”
Volcanic eruptions eject many different types of gases and particles. Most eruptions, including Hunga Tonga, release particles that cool Earth’s surface by reflecting sunlight back into space, but they typically dissipate after two to three years. Very few, however, blast water vapor so high. This water vapor can linger longer in the atmosphere — five to 10 years — and trap heat on Earth’s surface.
Millán speculates that the water vapor could start having a warming effect on the planet’s surface temperature once the accompanying cooling particles dissipate in about three years. He is unsure how much the temperature would increase, as it depends on how the water vapor plume evolves. The team suspects that the increased warming will last for a few years, until circulation patterns in the stratosphere flush the water vapor to the troposphere, the layer where Earth’s weather occurs.
“This is just a temporary warming, and then it will go back to whatever it was supposed to go back to,” Millán said. “It’s not going to exacerbate climate change.”
NASA atmospheric scientist Ryan Kramer added that, given the numerous factors that drive temperature changes on time scales of years, the warming effect from the volcano could also get lost in the noise, depending on its magnitude.
On a shorter time scale, the increased water vapor could also worsen ozone depletion in the stratosphere, said Susan Strahan, an atmospheric chemist with University of Maryland Baltimore County and NASA.
Stratospheric ozone protects the surface of Earth from damaging ultraviolet radiation. Chemicals that deplete the ozone layer were largely phased out through the 1987 Montreal Protocol and subsequent amendments.
Strahan, who was not involved in the study, explained that the excess water vapor will affect many chemical reactions that control stratospheric ozone concentrations. NASA satellite data in July already shows a decrease in ozone levels, compared with those in previous years in the location where the excess water vapor is most concentrated. She added that a full analysis would need to be conducted to tease out the cause.
“There are probably impacts right now, but what we need [is] a model to tell us is by what mechanism(s) did the impacts occur. Meteorology and chemistry will almost undoubtedly both play roles — the questions are how much, where, when?” Strahan said in an email.
Strahan also said the excess water vapor could enhance the formation of special noctilucent clouds, which appear as shimmering, ghostlike wisps in the night sky. They occur around 50 miles in the atmosphere, higher than the stratosphere, and are some of the rarest, driest and highest clouds on Earth. For many people, the clouds provide remarkable skygazing. However, researchers think any noticeable change in these clouds would not appear until later, depending on how long it takes for the water vapor to travel upward in the atmosphere where the clouds form.
Overall, Millán said the excess water vapor is nothing much to be concerned with on its own but “something that is just interesting that is happening.” He and his colleagues are taking this opportunity to test their computer models that help us understand climate change and weather forecasting in general.
“We have these massive amounts of water vapor moving in the stratosphere, and we can test how well the models reflect its movements within the atmosphere,” Millán said. “This volcano is going to give plenty of researchers a lot of work.”