Martin Jucker su The Conversation commenta un nuovo studio pubblicato sul Journal of Climate sugli impatti climatici dell’eruzione del vulcano sottomarino Hunga Tonga-Hunga Ha’apai (in breve Hunga Tonga), avvenuta il 15 gennaio 2022 nel Regno pacifico di Tonga.

Usually, the smoke of a volcano – and in particular the sulphur dioxide contained inside the smoke cloud – ultimately leads to a cooling of Earth’s surface for a short period.

This is because the sulphur dioxide transforms into sulphate aerosols, which send sunlight back into space before it reaches the surface. This shading effect means the surface cools down for a while, until the sulphate falls back down to the surface or gets rained out.

This is not what happened for Hunga Tonga.

Because it was an underwater volcano, Hunga Tonga produced little smoke, but a lot of water vapour: 100–150 million tonnes, or the equivalent of 60,000 Olympic swimming pools. The enormous heat of the eruption transformed huge amounts of sea water into steam, which then shot high into the atmosphere with the force of the eruption.

All that water ended up in the stratosphere: a layer of the atmosphere between about 15 and 40 kilometres above the surface, which produces neither clouds nor rain because it is too dry.

Water vapour in the stratosphere has two main effects. One, it helps in the chemical reactions which destroy the ozone layer, and two, it is a very potent greenhouse gas.

Secondo gli autori dello studio, l’impatto dell’eruzione sulle temperature medie globali sarebbe comunque modesto.

In terms of global mean temperatures, which are a measure of how much climate change we are experiencing, the impact of Hunga Tonga is very small, only about 0.015 degrees Celsius.