Particles blocking sunlight from a powerful explosion may not cool Earth’s surface temperature as much as previously thought, a new study suggests. About 74,000 years ago, the Toba volcano in Indonesia erupted in St. Petersburg in 1980. It exploded with a force 1000 times greater than the explosion of St. Helens. The mystery is what happened next—the extent to which this super-eruption lowered global temperatures.

The International Space Station crew photographed the eruption of Mount Etna in Sicily in October 2002. The ashfall was reported to be 550 miles away. But when it comes to explosive power, no modern explosion can match a supereruption that hasn’t occurred in tens of thousands of years.NASA

When it comes to the most powerful volcanoes, researchers have long predicted how global cooling following an eruption, sometimes called a volcanic winter, could potentially pose a threat to humanity. Previous studies agreed that there would be some cooling on the planet, but disagreed on how much. Estimates ranged from 3.6 to 14 degrees Fahrenheit (2 to 8 degrees Celsius).

In a new study published in the Journal of Climate, a team from NASA’s Goddard Institute for Space Studies (GISS) and Columbia University in New York used state-of-the-art computer modeling to simulate supereruptions such as the Toba event. They found that post-eruption cooling was unlikely to exceed 2.7 degrees Fahrenheit (1.5 degrees Celsius), even for the most powerful explosions.

“The relatively modest temperature changes we found most consistent with the evidence may explain why no supereruption has produced clear evidence of global catastrophe for humans or ecosystems,” said lead author Zachary McGraw, a NASA GISS and Columbia University researcher. .

To be considered a supereruption, a volcano must release more than 240 cubic miles (1,000 cubic kilometers) of magma. These explosions are extremely powerful and rare. The last supereruption occurred 22,000 years ago in New Zealand. The most famous example may be the eruption that erupted in the Yellowstone Crater in Wyoming about 2 million years ago.

Small snippets, big questions

McGraw and his colleagues set out to understand what causes differences in model-based temperature predictions because “models are the primary tool for understanding climate changes that occurred too long ago to leave a clear record of their severity.” They settled on a difficult-to-measure variable: the size of microscopic sulfur particles injected per mile into the atmosphere.

In the stratosphere (about 6 to 30 miles above), sulfur dioxide from volcanoes undergoes a chemical reaction to condense into liquid sulfate particles. These particles can affect the Earth’s surface temperature by two countermeasures: by reflecting incoming sunlight (causing cooling) or by capturing escaping heat energy (a type of greenhouse warming effect).

Over the years, this cooling phenomenon has also raised questions about how humans might reverse global warming by deliberately injecting aerosol particles into the stratosphere to provide a cooling effect, a concept called geoengineering.

Researchers have shown to what extent the diameter of volcanic aerosol particles affects the temperature after the eruption. The smaller and denser the particles, the greater their ability to block sunlight. But estimating the size of the particles is difficult because previous supereruptions have not left reliable physical evidence. The size of the particles changes during coagulation and condensation in the atmosphere. Even if the particles fall back to Earth and are stored in ice cores, they do not leave a clear physical record due to mixing and compression.

By modeling supereruptions at a variety of particle sizes, researchers found that supereruptions may not change global temperatures significantly more than the largest explosions of the modern era. For example, the eruption of Mount Pinatubo in the Philippines in 1991 caused global temperatures to drop by about half a degree in two years.

The mysteries of superburst cooling invite further investigation, said Luis Millan, an atmospheric researcher at NASA’s Jet Propulsion Laboratory in Southern California who was not involved in the research. He said the way forward is to conduct comprehensive model comparisons as well as more laboratory and model studies on the factors that determine the particle size of volcanic aerosol.

Given the ongoing uncertainty, Millan added: “To me, this is yet another example of why geoengineering by injecting an aerosol into the stratosphere is far from a viable option.” “Massive Global Cooling After Volcanic Super-Eruptions?” The study, titled “The answer depends on the unknown size of the aerosol,” was published in the Journal of Climate.