Dr Fommel said that any estimate of how much additional warming the Tonga eruption would add was highly speculative at this point. “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 what we’d expect from carbon dioxide, which is closer to 0.1 to 0.2 degrees per decade,” she said. Dr. 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, this should reduce the amount of ozone,” Dr. Fommel said. But this would be temporary, he said, because ozone formation and destruction is a “cycle that continues.”
Dr Solomon said that 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.