Scientists measure the force of eruptions using something called the Volcanic Explosivity Index, or VEI. (I learned about this from my teenage grandson, who has an encyclopaedic knowledge of volcanoes.)
The eruption of Hunga Tonga-Hunga Ha’apai had a VEI of 5 or 6, depending on which source you believe. According to NIWA, it was the biggest atmospheric explosion recorded in more than a century. As a point of comparison, the cataclysmic Oruanui (Lake Taupo) eruption about 26,500 years ago had a VEI of 8. Krakatoa (1883) scored a 6.
The subsequent tsunamis devastated parts of Tonga, claiming four lives there and even killing two people in Peru. The eruption also wiped out 55 km of undersea cable, but otherwise it aroused relatively little public attention. After all, it was a long way from anywhere in a very sparsely populated part of the globe.
Scientists, however, got very excited about it. An online search turns up numerous academic papers marvelling at the scale of the eruption and assessing its implications.
Why am I writing about this? Simply because I can’t help wondering whether Hunga Tonga might have something to do with the freakish weather the North Island has been enduring.
I can’t recall a wetter, more miserable summer. January rainfall in parts of the North Island was four times higher than normal; Auckland was the wettest ever. Campers, and especially those with kids, will remember 2023 as their annus horribilis.
The February figures will be far worse. We’ve just been through several weeks of catastrophic weather events and they may not yet be over.
In so far as there’s any explanation for these events, they are commonly (if vaguely) attributed to climate change, the implication being that it's human-induced. La Nina and “atmospheric rivers” have been cited, but in such a way as to imply that they are all part of the same pattern. Anyone who dares suggest otherwise, as Maureen Pugh did, risks being put in the stocks. But is there more to it than that?
Before anyone rushes to denounce me, I’m not a climate change denier. I’ m not in a position to deny anything, since I don’t possess the scientific knowledge to make definitive assertions. My own amateur observations tell me the climate is changing; the winters are warmer (we seem to get far fewer frosts in Masterton than 20 years ago) and the frequency of slips on the Remutaka Hill road is a very basic pointer to heavier and more frequent rain. Weather bombs that were once exceptional are now the norm.
Nonetheless, the science on climate change is contradictory and often freighted with ideology – so yes, I’m sceptical. I think journalists and scientists have a duty to be sceptical.
Oh, and another disclaimer: I’m generally clueless when it comes to science. When I began my fifth form year (today’s Year 11) at Central Hawke’s Bay College, I was thrilled to discover that science had quietly been dropped from my curriculum. I was such a no-hoper that my teachers decided, without any consultation, that there was no point wasting my time or theirs. The same thing had happened with maths the previous year.
But while acknowledging I’m an ignoramus, I think I have a legitimate question to ask. Even accepting that the climate is changing, what has happened this summer seems qualitatively different. It has not only been brutal and extreme but abrupt, persistent and viciously repetitive – too much so, surely, to have been simply a continuation of a familiar long-term trend. It just seems too easy – too glib, almost – to put it all down to human-induced climate change.
Which brings me back to Hunga Tonga. Notwithstanding my lack of scholarship, it seems obvious to me from the various academic papers published about the HT eruption that it had meteorological consequences. One study, published by the French National Center for Scientific Research, called it the most remarkable climate event of the past three decades. There’s a clue, right there.
Another paper, published by the American Geophysical Union, had this to say: “The violent Hunga Tonga-Hunga Ha'apai eruption on 15 January 2022 not only injected ash into the stratosphere but also large amounts of water vapor, breaking all records for direct injection of water vapor, by a volcano or otherwise, in the satellite era.
“The massive blast injected water vapor up to altitudes as high as 53 km. Using measurements from the Microwave Limb Sounder [no, I don’t know what that means either] on NASA's Aura satellite, we estimate that the excess water vapor is equivalent to around 10% of the amount of water vapor typically residing in the stratosphere. Unlike previous strong eruptions, this event may not cool the surface, but rather it could potentially warm the surface due to the excess water vapor.”
The study also notes that “the H2O injection was unprecedented in both magnitude and altitude” and says it may take several years for the water plume to dissipate.
I admit that much of the paper is incomprehensible to me, but am I wrong to assume that a phenomenon of that scale is going to affect weather patterns?
Yet another study, published in Nature Climate Change, similarly noted that the HT eruption had expelled an unprecedented amount of water into the atmosphere and could cause an increase in global surface temperatures lasting several years. So there seems to be some sort of consensus.
I learned that volcanic eruptions can have a profound impact on the weather when, in a past life as a wine writer, I heard New Zealand winemakers bemoaning the Pinatubo years.
The 1991 eruption of Mt Pinatubo, in the Philippines, had a VEI of 6. It produced what’s called a volcanic winter, reducing the amount of sunlight reaching the earth’s surface by 10 percent – hence the challenge of getting grapes to ripen even in distant New Zealand. Pinatubo’s eruption is also thought to have triggered the so-called Storm of the Century in 1993.
Hunga Tonga, being an underwater eruption that produced a plume of water rather than clouds of dust that absorbed sunlight, had a different effect, leading to the predictions of rising global temperatures.
Either way, it seems safe to assume the eruption will have had an effect on the weather. And being a lot closer to New Zealand than Mt Pinatubo, doesn’t it stand to reason that its impact is likely to be more pronounced?
Bearing all this in mind, it doesn’t seem fanciful to suggest that Hunga Tonga might have played a hand in the apocalyptic weather events of the past two weeks. But I wonder if that likelihood is being played down because it conflicts with the human-induced climate change narrative so feverishly promoted by the Greens and now apparently accepted by the National Party – and enforced by sections of the media.
To put it another way, are we in a Fawlty Towers-type scenario where the implicit understanding is that no one should mention Hunga Tonga? (To quote Basil Fawlty, I just did, but I think I can get away with it.)
There are people who read this blog who are far better informed than I am on matters of science. I would welcome their input, even if it results in my theory being – for want of a better expression – blown out of the water.
Karl du Fresne, a freelance journalist, is the former editor of The Dominion newspaper. He blogs at karldufresne.blogspot.co.nz.