Millions of tonnes of water vapour have been lingering in the atmosphere since the Hunga Tonga-Hunga Ha’apai volcano erupted in 2022– possibly contributing to global warming
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| The Hunga Tonga-Hunga Ha’apai volcano in January 2022, days before the eruption (Credit: Macar Via Getty Images) |
Most of the nearly 150 million tonnes of water vapour launched into the air by the underwater eruption of the Hunga Tonga-Hunga Ha’apai volcano in 2022 remains there, setting record concentrations in many parts of the atmosphere.
“It’s really a very special, unprecedented event,” says Christian von Savigny at the University of Greifswald in Germany.
The South Pacific eruption was the first such event to occur when researchers could observe it with satellites. It led to a flurry of research into its influence on global climate, including the limited warming effect of the water vapour, which is a greenhouse gas. The eruption increased the concentration of water vapour in the stratosphere – located between around 6 and 50 kilometres above Earth – by as much as 15 percent, and unlike other eruptions, it didn’t release much sulphur, which has a cooling effect. Previous research suggested this small warming effect would continue until 2035.
Gerald Nedoluha at the Naval Research Laboratory in Washington DC and his colleagues measured concentrations of water vapour in the stratosphere and the higher mesosphere in the years since the eruption using a microwave instrument aboard NASA’s Aura satellite, as well as several ground-based instruments.
They found that, in November 2023, concentrations were still elevated in much of the atmosphere above 17 kilometres, indicating that most of the water vapour from the eruption remained aloft nearly two years later. Over that period, they found concentrations in much of the stratosphere and large parts of the mesosphere above it broke records extending back 20 years.
It is not surprising that the water vapour has stuck around given there are no major sinks for the vapour besides the slow cycling of the stratosphere and decomposition by sunlight, says von Savigny, who was not involved with the research.
But the ability to track the plume of water vapour in such detail has enabled atmospheric scientists to gain insights on how such eruptions influence the climate, from the possible depletion of the ozone layer to cloud formation.
For instance, von Savigny says water vapour from the eruption has now reached an altitude of 90 kilometres, settling in a region of the atmosphere called the mesopause. This has enabled his team to watch for the first time how the added water will affect rare noctilucent clouds, which were first observed about two years after the eruption of Krakatoa in 1883 – the last time a volcano launched so much water into the sky.
Journal reference:
JGR Atmospheres DOI: 10.1029/2024JD040907
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