The eruption of an underwater volcano in the Pacific Ocean in January triggered a global shockwave, releasing huge amounts of water vapor into the upper atmosphere, where it could cause a slight short-term rise in global warming, scientists said Thursday. .
Injecting what the researchers estimated to be at least 55 million tons of water vapor into the stratosphere could temporarily deplete the protective ozone layer in the atmosphere, they said.
The eruption of the Hongi Tonga-Hungia Hawapai volcano on the island of Tonga on January 15 was the largest in decades. It triggered a tsunami that devastated parts of Tonga, as well as smaller tsunamis thousands of miles away caused by changes in air pressure during the shock wave that circled the globe.
Because it occurred about 500 feet underwater, the eruption of extremely hot molten rock also caused seawater to explode explosively into steam. A plume of water vapor, volcanic gases, and ash reached an altitude of 35 miles. This increased the amount of water vapor in the stratosphere, which ends at an altitude of 31 miles, by at least 5%.
“It’s completely unique,” said Holger Vommel, chief scientist at the National Center for Atmospheric Research in Boulder, Colorado. “This didn’t happen because we were able to measure water vapor in the stratosphere, which started about 70 years ago.. “ Vommel is the lead author of a paper published in Science on the findings.
Like carbon dioxide and other greenhouse gases, water vapor absorbs heat in the form of infrared radiation from the Earth’s surface and re-emits it. Therefore, adding a large amount of water vapor is expected to increase the warming for several years until the gas dissipates.
Large eruptions of terrestrial volcanoes do not release much water vapor, but they can inject huge amounts of sulfur dioxide into the stratosphere, which can have a short-term cooling effect. After the most recent eruption of Mount Pinatubo in the Philippines in 1991, average global temperatures dropped by 1°F, or 0.6°C, for more than a year.
Any estimate of how much additional warming the Tonga eruption would add was highly speculative at this point, Fommel said. “But I wouldn’t be surprised if they were the same size” as Pinatubo, he said, just in reverse. He added that the additional warming will likely last longer than cooling after Pinatubo.
Susan Solomon, an atmospheric scientist at MIT who described the temperature effects of changes in stratospheric water vapor in a 2010 study, said the Tonga eruption “could add something on the order of 0.05 degrees of warming to average global temperatures.” ‘Maybe for three to five years.
“That’s lower than we would expect from carbon dioxide, which is closer to 0.1 to 0.2 degrees per decade,” she said. Solomon was not involved in Tonga research.
All this water vapor will likely also change the chemistry of the atmosphere that destroys ozone, the oxygen molecule that protects life on Earth from harmful ultraviolet rays from the sun.
“By significantly increasing the amount of water vapor, that should reduce the amount of ozone,” Vommel said. But that would be temporary, he said, because ozone formation and destruction is a “cycle that goes on.”
Any loss of ozone near the boundary of the stratosphere and lower atmosphere would also likely lead to some surface cooling, which would counteract warming from the added water vapor, Solomon said.