Excess stratospheric H2O will persist for years, could affect stratospheric chemistry and dynamics and may lead to surface warming
Volcanic eruption in Tonga recorded January 15, 2022 is likely to add to global warming and the depletion of Earth’s ozone layer, according to a new study.
The violent underwater eruption of Hunga Tonga-Hunga Ha’apai injected 146 teragrams (1 teragram equals a trillion grams) of water vapour into the stratosphere. The stratosphere is the layer of atmosphere between 10-50 kilometres above the surface of the Earth.
The water vapour, a greenhouse gas, released by the volcano, is roughly 10 per cent of the water already present in the stratosphere, noted the study published in Geophysical Letters July 1, 2022.
“Tonga eruption may be the first volcanic eruption observed to impact climate not through surface cooling caused by volcanic sulfate aerosols, but rather through surface warming caused by excess water vapour,” the study noted.
The eruption injected an unprecedented amount of water — enough to fill 58,000 Olympic-size swimming pools, researchers from the National Aeronautics and Space Administration (NASA), The University of Edinburgh and NorthWest Research Associates wrote. A typical Olympic pool measures 50 meters (m)long, 25 m wide and 3 m deep.
“We’ve never seen anything like it,” Luis Millán, an atmospheric scientist at NASA’s Jet Propulsion Laboratory in Southern California, said in a statement.
Volcanic plumes often contain carbon dioxide, sulfur dioxide (SO2), hydrogen chloride (HCl) and other trace gases. Massive emission of SO2 often cools the planet as it forms compounds that reflect incoming sunlight.
The Mount Pinatubo eruption, 1991 is believed to have lofted 17 teragrams of SO2 and lowered temperatures by 0.5 degrees Celsius.
To analyse the impacts of the Tonga blast on global climate, Millán and his colleagues used Microwave Limb Sounder, a device that measures atmospheric gases.
Their analysis showed that Tonga did not inject vast amounts of either HCl or SO2 into the stratosphere.
It spewed 0.41 teragrams of SO2, much lower than the 1 teragram released by each of the three recent volcanic events — the 2008 Kasatochiin Alaska, the 2009 Sarychev, Russia and the 2019 Raikoke, Russia eruptions, the study pointed out.
At the same time, an unprecedented amount of H2O was injected by the volcano. This excess stratospheric H2O will persist for years, could affect stratospheric chemistry and dynamics and may lead to surface warming, the study noted.
The unprecedented amount of water released could be explained by the underwater volcano’s caldera — a large depression left after a volcano erupts and collapses.
“The caldera was about 50 m below the surface, making conditions ripe for the release. If it were shallower, there would not have been enough superheated seawater to reach the stratosphere,” the researchers explained.
And if it were located at greater depths, the immense pressures in the ocean’s depths are likely to have softened the release, they added.
Though the Kasatochi event, 2008 and the Calbuco eruption, 2015 in Chile injected appreciable amounts of water vapour, they dissipated quickly, the researchers highlighted.
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