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Uptick in Global Volcanic Activity: Climate Change – Wully Davidson

Global volcanic activity has recently increased by 125%…. will it have any effect on climate change?

There seems to have been an uptick in news stories of volcanoes erupting around the globe, recently. One small, but quite spectacular example, is the appearance of new fissures spewing lava from Geldingadalur valley in Iceland. It’s the first known eruption there in 800 years, and I’ve spent a good few hours watching the live feed on Youtube. It’s fascinating stuff, but fairly insignificant on the global volcanism scene.

Etna is constantly erupting, but there has been a recent remarkable increase in activity there, lasting for much longer than previous episodes, which now seems to be subsiding. Guatemala’s Pacaya volcano has been erupting frequently since 1961, but there has also been a recent dramatic increase in activity there, too. Lava flows began on March 18, causing wildfires, and destroying coffee and avocado plantations.

La Soufriere Volcano, St Vincent

https://commons.wikimedia.org/wiki/File:Soufriere.jpg

On the island of St Vincent, in the Caribbean, La Soufriere volcano began to show increased activity in December. Explosive eruptions began on April 9, and have recently subsided, but could continue for months. Previous explosive eruptions occurred in 1718, 1812, 1902, and 1979. The 1902 eruption killed 1,680 people, and occurred just hours before the eruption of Mount Pelee, on the island of Martinique, 100 miles to the north of St Vincent. The 1902 Mt. Pelee eruption was the worst disaster attributed to volcanism in the 20th century, killing 29,000 people. Mt. Pelee also began to show increased activity in December.

So, is there a real increase in volcanic activity lately, or might it just be increased reporting, and what, if any, effect might this have on climate change? A quick google showed that, at the end of March, there were 45 active volcanic eruptions per day, compared with an average of 20. So, global volcanic activity has recently increased by 125%.

Influence of Volcanic Activity on Climate Change

That’s a pretty significant increase, but will it have any influence on climate change? Probably not much. Let’s quickly eliminate one particular myth promulgated by climate change deniers – that volcanoes emit more CO2 than human activity. It has been estimated that volcanoes contribute around 1% of man made CO2 annually. So, that’s dismissed.

Eruption Column Mount Pinatubo U.S. Geological Survey Photograph taken by Richard P. Hoblitt., Public domain, via Wikimedia Commons

Next, volcanoes eject vast amounts of sulfur dioxide (SO2) into the stratosphere, where it reflects back sunlight, cooling the planet. It can remain in the stratosphere, above the weather, for 2 years, whereas SO2 in the lower atmosphere will be rained out in a few days as acid rain. The eruption of Mount Pinatubo, in the Philippines in 1991, was a once in a lifetime event. It erupted for five months, and ejected an estimated >10 km3 of material, including 19 million tons of SO2 into the stratosphere, and this cooled the planet by about 0.2 C for the following two years. No one really noticed, though.

The Volcanic Explosivity Index (VEI) is a logarithmic scale for the magnitude of volcanic eruptions. The greatest eruption of the 20th century was actually the little heard of ‘Novarupta’ eruption, in Alaska, in 1912. However, there was no detectable global cooling after this event, perhaps due to its northerly latitude. Pinatubo, Novarupta and Krakatoa (1883) all have a VEI designation of 6, ejecting more than 10 km3 of material. They can be expected to occur once in 50 to 100 years

Eruption of Mount Tambora – ‘year without a summer’

Jialiang Gao (peace-on-earth.org), CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons

The eruption of Mount Tambora, in Indonesia, in 1815, is regarded as the most explosive eruption since the beginning of the Holocene period, which began after the end of the last Ice Age, 11,500 years ago. It occurred before global temperature monitoring, so no one really knows how much global temperature cooled as a result. But the following year, 1816, was known as the ‘year without a summer’ in North America and Europe. There were crop failures and livestock deaths, resulting in the worst famine of the century. It had a VEI rating of 7, so about 10 times greater than Pinatubo, ejecting >100 km3 of material. Other VEI 7 rated events are Taupo (New Zealand) in 180 AD, and Thera (Santorini, Aegean Sea) c. 1620 BC. VEI 7 events can be expected to occur every 500 to 1,000 years

VEI 8 rated events are the stuff of nightmares, 100 times more violent than Pinatubo. Thankfully, they are extremely rare, but it’s probably true to say that only a few of those that have occurred have actually been identified. They eject more than 1,000 km3 of material. Examples are Taupo (NZ, 26,500 BC), Toba (Indonesia 74,000 BC) and Yellowstone (US 630,000 BC). They can be expected every 50,000 + years. The most recent estimates for the material ejected by Taupo is 3,200 km3.

The Toba Eruption

It has been suggested that the Toba eruption resulted in a catastrophic global cooling for several years, which greatly diminished the global human population. The total mass ejected has been estimated as at least 12 times that of Tambora, and south east Asia is believed to have been covered in six inches of volcanic ash. So, volcanism can, indeed, have catastrophic effects on climate. Just not very often.

La Nina Cooling Effect on Global Temperature

The first three months of 2021 have been the coolest start to the year since 2014, almost certainly mainly due to the cooling influence of the now weakening La Nina in the Pacific. La Soufriere is unlikely to match Pinatubo for SO2 emissions, but is estimated to have outgassed 2% of the SO2 produced by Pinatubo in a single day, which is impressive. If the current uptick in global volcanism continues for a few more months it ought to have a small, but noticeable cooling effect on global temperature. That, combined with La Nina, is likely to result in 2021 being an anomalously cool year, compared with recent years.

Wully Davidson, April, 2021

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