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SYFY WIRE volcanoes

No sunscreen could have saved us from a supervolcano with the power of a nuclear war 

By Elizabeth Rayne

There is really nothing over SPF 50 that can give you more protection from the sun, except for retreating into the shadows like a vampire. Granted, slathering on sunscreen probably wouldn’t have saved you if you were around when the Toba volcano erupted in what is now Indonesia.

Around 74,000 ago, Toba really lost its temper. It unleashed gobs of molten magma and so much sulfur dioxide that it ate away half the ozone layer. How exactly the aftermath of this beast affected humans has been debated over and over, but now an international group of scientists, using a NASA climate model to determine what happened in the wake of Toba’s eruption, have finally found out how it devastated human populations. Lethal sunburns were just the beginning of what would turn out to be an era of death.

After the heat came a deep freeze. Much like the asteroid that set off volcanoes all over the planet and eventually took down the dinosaurs, aerosols and ash accumulated in the atmosphere and blocked sunlight. Earth was plunged into a nuclear winter. The shroud of ash and gases that blocked photons (light particles) and sent temperatures plummeting only made UV exposure worse. With half the ozone layer gone, 15 minutes would would get you more than burned, but also put you at risk for eye damage, skin cancer, and warped DNA. Going outside was a hazard to human survival.

“The Toba plume strongly inhibited oxygen photolysis, suppressing ozone formation in the tropics, where exceptionally depleted ozone conditions persisted for over a year,” said a group of researchers in a  recently published  study in Nature Communications Earth & Environment. “This effect, when combined with volcanic winter in the extra-tropics, can account for the impacts of supereruptions on ecosystems and humanity.”

Sulfur dioxide (SO2) is doom for ozone because of how it gets in the way of ozone production. Ozone forms from atmospheric oxygen when photons break the bond between the two oxygen atoms in an O2 molecule. This is photolysis. What a volcano vomits into the sky will block sunlight and solar heat, but that hardly means it would have been safe out there even with sunscreen.


Massive amounts of sulfur dioxide absorb UV radiation. In the absence of photons from sunlight, ozone cannot form, which means a gigantic hole in the ozone layer, but Earth will still get bombarded by invisible UV rays.

With the ModelE digital climate model from NASA’s Goddard Institute, simulations showed how destructive Toba actually was. It turned out that this ancient volcano belched out a hundred times more sulfur dioxide than the 1991 eruption of Mt. Pinatubo in the Philippines. The tropics were hit especially hard, experiencing more depletion than there was over Antarctica until that ozone hole finally closed last year, and tropical regions are more diverse than anywhere else on Earth. Species we never knew of (and never will) may have gone extinct. Nuclear winter conditions were at their worst in the northern hemisphere. Ozone levels took three years to recover.

“The UV index increase…over a period of about a year is likely to have had critical consequences for humanity,” the researchers also said in the study. “The range of possible UV impacts is extensive, with environmental, ecological, health-hazardous, and societal consequences.”

Sunburn aside, one of the scariest consequences of too much UV exposure is DNA damage that can also causes skin cancer. Some stagnation in the human population after Toba can be explained because no treatments for cancer existed tens of thousands of years ago. UV rays can tear apart molecules of thymine, one of the four main nucleotides, or chemical bases, in DNA. It can repair itself if the damage hasn’t gone too far. Excessive UV exposure like that brought on by Toba can disrupt cellular function and repair processes. When cells are unable to function properly, they can turn cancerous or die off.

You should be wearing SPF every single day. Just in case you forget, let the Toba eruption be a reminder of the bodily wreckage UV rays are capable of.

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