The Hunga Tonga-Hunga Ha’apai volcano in January 2022, days before the eruptionMaxar 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…