Are supervolcanoes not as dangerous as thought?

In some places on this planet, people are living on a gigantic geological time bomb: a supervolcano. The Yellowstone Caldera in the US and the Toba in Indonesia are well known. One of these dangerous monsters is not far from Switzerland – it is the Phlegraean Fields (“Campi Flegrei”) near Naples, which have also been disturbingly active lately.

The well-known Vesuvius is very close, and these two volcanoes can be used to clearly illustrate the difference between the volcano types: While Vesuvius dominates the Gulf of Naples with its cone, the Phlegraean Fields are a huge, but generally quite flat volcano . beaks. Because of their enormous magma chambers, supervolcanoes do not form typical volcanic cones, but leave behind gigantic cauldrons in the ground after eruptions, so-called calderas.

And when supervolcanoes explode, they send enormous amounts of ash and sulfur into the stratosphere. Not only would this be devastating to their regional environment, but scientists fear that in extreme cases it would lead to a massive cooling of the global climate, a ‘volcanic winter’. This could – like a so-called nuclear winter after a nuclear war – bring humanity to the brink of extinction.

An example of this is the eruption of the Toba supervolcano on the Indonesian island of Sumatra 74,000 years ago – the strongest eruption in the past two million years. According to the controversial Toba catastrophe theory, the resulting global cooling of 3 to 5 degrees Celsius was responsible for a drastic drop in human numbers to several thousand. This ‘genetic bottleneck’ was identified by analyzing human mitochondrial DNA.

The cooling effect of sulfur and ash particles in the atmosphere is well known. Volcanic eruptions in recent decades, using modern measuring methods, have proven this: during the 1991 eruption of Mount Pinatubo, a total of 17 million tons of sulfur dioxide entered the stratosphere, temporarily reducing incoming sunlight by 5 percent. This resulted in a global temperature drop of about 0.4 degrees over the next year and a half.

However, it is not yet known how severe the global cooling will actually be as a result of the eruption of a supervolcano; there are only simulations. Estimates published so far indicate a cooling effect of 2 to 8 degrees Celsius. But a new study published in the Journal of Climate arrives at significantly lower values.

The researchers from NASA’s Goddard Institute of Space Studies (GISS) and Columbia University in New York conclude that the cooling effect of such supervolcanic eruptions should not exceed 1.5 degrees Celsius, which is on the order of “normal” . eruptions » Volcanoes is established. This is the result of several simulations that modeled the eruption of a supervolcano similar to Toba.

Physicist Zachary McGraw, who was involved in the research, explained in a statement from the AIVD:

A supereruption refers to an eruption that releases at least 1,000 cubic kilometers of magma (see info box above). The last such supereruption occurred in New Zealand more than 22,000 years ago.

In their simulation, the researchers focused on the question to what extent the particles released into the atmosphere influence the temperature. The sulfur particles condense in the stratosphere – this is the second layer of Earth’s atmosphere adjacent to the troposphere, extending from about 15 to 50 kilometers high – to form liquid sulfate particles.

These particles affect the surface temperature on Earth in two different ways: first, they reflect sunlight, which leads to a reduction in solar radiation on Earth and thus has a cooling effect. On the other hand, they can block the heat radiation emitted from Earth to space, which is a kind of greenhouse effect.

The smaller and denser the sulfur particles, the greater their ability to block sunlight. The simulations with different sizes of these sulfuric acid droplets also led to extremely different effects on temperature, ranging from extreme cold to global warming. Estimating particle size is obviously difficult because there are no reliable data from previous supereruptions.

The analysis of the simulations ultimately showed that the effect of supereruptions on the climate is limited. Therefore, even the most powerful eruptions of supervolcanoes have not left tangible traces in the history of life on Earth.

This finding could also have an impact on the discussion about using sulfur particles to cool the Earth’s climate, so-called solar radiation management. The proponents of this controversial geoengineering method point to the cooling of the global climate due to sulfur particles released into the atmosphere by volcanic eruptions and argue for the artificial introduction of large amounts of sulfur into the stratosphere.

However, the results of the new study underline that there is still a great need for research in this area. The influence of volcanic eruptions on Earth’s surface temperature is still poorly understood, and it would therefore be remiss to massively intervene in Earth’s geochemical cycles with such large-scale engineering projects. For example, the question would first have to be clarified how large the sulfur particles actually were in a supereruption.