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Eruption adds to weather bomb

The volcanic eruption in Tonga last year may have contributed to some of the heavy rainfall we’ve weathered recently, but climate change carries more of the blame, an expert has told the Times-Age.

When Hunga Tonga–Hunga Ha’apai erupted in January 2022, it unleashed a colossal amount of energy – equivalent to about 4–18 megatons of TNT, according to a preliminary estimate by NASA scientists.

Reports have suggested the eruption could keep weather wild for years to come, but National Institute for Water and Atmospheric [Niwa] Research climate modeller Dr Olaf Morgenstern said it was nothing compared to the long-term effects of climate change.

Global warming can be measured in terms of the change in radiation flux at the top of the atmosphere, and the carbon dioxide added to the atmosphere by humans.

It is that retained energy that is warming the oceans and the atmosphere, Morgenstern said.

“The additional water due to the Tonga eruption is of the order of 0.1 watts per square metre. So it’s certainly not on the same scale as human-induced warming but might produce noticeable additional warming for a few years.”

Morgenstern said scientists expected to see an increase in the frequency of heavy rain as the world continued to warm.

“I’m not aware of any studies that relate the Tonga eruption to extreme events, but such a link cannot be ruled out,” he added.

The 2021 Intergovernmental Panel on Climate Change [IPCC] report said that every fraction of a degree of additional warming to the planet increases the chances of extreme rain events.

“The eruption might be raising temperatures by a fraction of a degree. But really, we can only speculate here.”

Morgenstern said it was interesting to note the biggest eruption in the last 50 years before the Tonga eruption – Mt Pinatubo in 1991 – had a cooling effect on the climate because it produced far less water but more cooling sulphate aerosol droplets.

The Tonga eruption produced significantly more water, so the effect could be different.

Morgenstern said meteorology played a leading role in the severe weather New Zealand has seen recently.

In addition to climate change and the Tongan eruption, the La Nina phenomenon was increasing the likelihood of extreme weather events.

“El Nino and La Nina are like a seesaw that goes back and forth every few years.

“During the present La Nina conditions what has happened in Auckland was more probable than during El Nino.

“But human-made climate change is loading the atmosphere with more and more water, which makes such events increasingly likely to be record breakers,” Morgenstern said.

While the potential effects of the eruption will subside over the next few years, climate change won’t – almost every record-setting weather event these days is “almost impossible to imagine without climate change”.

Grace Prior
Grace Prior
Grace Prior is a senior reporter at the Wairarapa Times-Age with a keen interest in environmental issues. Grace is the paper’s health reporter and regularly covers the rural sector, weather, Greater Wellington Regional Council, and coastal stories.

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