Supereruptions and volcanic winters: how to survive them?

Super volcanoes release massive volumes of sulphur into the atmosphere. They form a dense haze and envelop the planet in a dark aerosol, sometimes for years. During such a volcanic winter, the ability of plants to perform photosynthesis decreases, shaking the food pyramid to its core. How can humanity protect itself from the worst effects of a super eruption? New ways of growing food, such as with little or no sunlight, may be amongst the answers.

Text: Kathelijne Bonne

In research, attention tends to go to jaw-dropping achievements such as detecting gravitational waves, imaging black holes and editing genes. These are all stunning, inspiring and useful. But major natural disasters and their aftermath also deserve serious investigation and coverage, even if they are rather spine chilling than exhilarating.

On 28 December I gave a lecture in Flanders, Belgium, on the restless Campi Flegrei volcano in the Gulf of Naples, the magnitude of eruptions it is capable of, and whether it will erupt again. Ashes from the Campanian Ignimbrite eruption 39,000 years ago was found as far away as Greenland, and the disaster may have contributed to the collapse of Neanderthal populations in Italy and Europe. Bringing up such a haunting topic raises a series of questions: what if another mega eruption were to occur, in the overpopulated Campi Flegrei (*) or elsewhere? Can modern society cope with a volcanic winter? What if crops fail on a large scale? How will that ripple across the global geopolitical minefield?

(*) The likelihood of a very large eruption in Campi Flegrei any time soon is very small. A small eruption is more likely.

The solution lies in the same vein as what can already be done to deal with the effects of climate change and population growth, and to combat famine; i.e., ways to feed humanity more efficiently, produce more food with less impact, and most importantly, on less area.

Source of all life 

The idea of volcanic winters and years of darkness reveals something crucial: "humans are beings of light"(*1), as Thomas Halliday, author of Otherlands, wrote in the chapter on life in the ocean's midnight zone. Humans, - and all the plants, animals and organisms we are connected to through complex interactions in the food web -, are ultimately nourished by sunlight.

Photosynthesis is, with few exceptions, the only way in which the so-called primary producers - plants, algae and bacteria - transform non-life into life, or in other words, convert carbon dioxide into organic molecules such as sugars. This is how they keep their vital spark alit and form the foundations of all ecosystems as well as all human food production.

To perform photosynthesis, plants need to bask in the sun, doing so standing side by side. This implies that agriculture is a two-dimensional affair, and takes up a lot of space. It may sound as if this is a drawback of photosynthesis itself, but it is not. Photosynthesis has sustained life for billions of years. The enormous expanses of land needed to produce food and other products for humans is primarily due to the predatory way we exploit nature and to our overindulgences and excesses (food waste, imported food, too much meat, which means feeding a surplus of tens of billions of farm animals, ...).

And if the sun, our ultimate source of life, goes into hiding for a few years behind a dense aerosol of sulphur, the conventional way of farming will spectacularly fail to meet the demands (it hardly does now in the current climate crisis), with grim consequences.

VEI 8 eruptions

Large eruptions, especially those with a volcanic explosivity index (VEI) of 6, 7 and 8, can disrupt climate in complex ways: they disrupt monsoons, El Niño phenomena and atmospheric and oceanic circulation. Famine, war and upheavals in society have been linked to major eruptions in the past, such as Tambora (Sumatra, 1815), notorious for a year without a summer and two hundred thousand deaths in Europe.

The volcanic explosivity index ranges from zero to eight. It expresses the volume of magma released in a single eruption. VEI zero is not explosive, like Hawaii. Mount Saint Helens (1980) and Vesuvius (79 AD) scored 5; Pinatubo (1991) and Tonga (2022) 6, and Campi Flegrei and Tambora 7.

These volcanoes pale in comparison to the VEI 8 volcanoes or supervolcanoes: Yellowstone (USA), Toba (Sumatra) and Taupō (New Zealand), among others, capable of "mega-colossal" eruptions, pulverizing more than one thousand cubic kilometers or 240 cubic miles of magma in a single blast. VEI 8 volcanoes erupt very rarely, once every ten to a hundred thousand or even millions of years. The last VEI 8 eruption is therefore long forgotten: Taupō, 25 thousand years ago.

The day a supervolcano will awaken, we will know.

Toba catastrophe theory

The potentially most destructive VEI 8 volcano is Toba in Indonesia. Its eruption of 74,000 years ago was the largest of the Quaternary (last two million years). According to the Toba catastrophe hypothesis early human populations collapsed, causing genetic bottlenecks. But according to more recent interpretations, the disaster was less catastrophic and of shorter duration than previously thought. Especially striking is the very uneven impact; people in the northern hemisphere were hit much harder than those in Africa. The Toba eruption is being simulated in many ways as a test-case for a future scenario.

Food without light

When plants perform photosynthesis, they metabolize only a small percentage of the incident solar energy. The efficiency is hence fairly low. Scientists have been busy figuring out how to boost the efficiency (more biomass with less light) by editing plant DNA through ultra-precise CRISPR-Cas techniques. This has yielded successes, for example in rice.

But when considering the possibility of super-eruptions, knowing how to grow food without photosynthesis may be a good thing too. Without light, growing containers can be stacked vertically, thus requiring less space. Space agencies are also investigating this matter so that astronauts can feed themselves on long missions, away from the sun, aboard a spacecraft or on some faraway planet.

Without the sun, another energy source is needed - preferably a renewable one - to capture carbon dioxide and produce organic substrates as food for plants. Some crops have already shown that they can metabolize acetate-containing substrates in total absence of light, but this is not yet possible on a large scale and would require profound reprogramming of plant genes.

Edible microorganisms?

There are other ways, potentially more feasible but less popular because of questionable palatability: growing edible microorganisms, yeasts, molds and fungi. According to Thomas Linder in "Edible microorganisms -An overlooked technology option to counteract agricultural expansion", microorganisms grow quickly and can be selected for the right proportions of proteins, healthy fats, vitamins and carbohydrates. Conditions in the culture tanks can be tuned very precisely, again requiring much less space than normal agriculture. The organisms can be fed with all kinds of substrates (e.g., methanol). One advantage is that this type of food production can be combined with new, green technologies to remove carbon dioxide from the atmosphere.

The question of whether people want to eat it is irrelevant in a natural disaster scenario. If we are starving, we will eat anything. Who knows, someday we might fight over a plate of molds topped with a coulis of bacteria.

Black smokers

Nature, too, has a few ecological niches where life thrives independently of light. In extreme environments, such as on the deep ocean floor and around black smokers, microorganisms engage in chemosynthesis - using chemical energy released from redox reactions - to produce biomass and sustain an entire community of the most unimaginable deep-sea creatures. Perhaps chemosynthesis was the first form of metabolism on Earth, until some bacteria "saw the light" and began photosynthesis, starting a revolution. Possibly chemosynthesis sustains living worlds in oceans under the icy oceans on the moons of Jupiter, Saturn, or on exoplanets in the habitable zones of their star.

Photosynthesis was the engine of all life on our planet for a few billion years and still is today, but by our own doing we have reached a tipping point and can - must - devise alternative solutions to become more resilient in the long run.

Fortunately, some time after a supereruption, the sulphur acids in the aerosols disintegrate, and the sun rays break through the haze. Plants will start growing and flowers will turn their heads towards the sun to receive its warmth and light. And so will the people who survived.

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Food for all, it remains the primary concern of humanity, today and in the future. Read about fertilizer and nitrogen and how they are linked to biogeochemical cycles. Or about the myth of sustainable meat and why we can't all be carnivores. Tonga, the volcano that erupted in 2022 was a VEI 6 but did somehow not affect climate. Or read about the role of volcanoes during the 'Great Dying' of nearly 90% of all life, at the end of the Permian. I wrote about the Campi Flegrei and the Gulf of Naples three times so far, about the volcano itself, about plastic pollution, and the three heads of Cerberus (volcanoes, plastic and mafia). And what about those other, lesser known volcanoes in Europe? 

Kathelijne: I am intrigued by how earth, life, air, ocean and societies interact on geological and human timescales.

Why I started GondwanaTalks.

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