Massive volcanoes could cool Earth more in a warming world

There are few forces on Earth more powerful than a large volcanic eruption. At their most potent, volcanoes inject millions of tons of Sun-blocking particles high into the atmosphere that can cool Earth for nearly 5 years, endangering crops and leading to “years without summer.” The most recent, the Philippines’s Mount Pinatubo eruption in 1991, caused a temporary 0.5°C drop in global temperatures.

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Before humanity started in on its planet-altering course, volcanoes were one of the biggest climate players. Over the long term, they belched carbon dioxide from Earth’s interior, causing warming. But in the short term, their sulfur gases often react with water to form highly reflective particles called sulfates, triggering spells of global cooling. Dark smudges of ash littering ice cores—our best evidence of these early eruptions—are a dim reflection of the wild weather left in their wake.

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But the opposite is also true, it turns out: Climate can have a big impact on volcanoes. In the new study, Thomas Aubry, a geophysicist at the University of Cambridge, and colleagues combined computer simulations of idealized volcanic eruptions with a global climate model. They simulated the response to plumes released from midsize and large volcanoes both in historical conditions and by 2100, in a scenario when Earth is predicted to warm very rapidly.

The researchers found two countervailing trends. Normally just one or two midsize volcanic eruptions shoot through the troposphere each year, bypassing this cradle of Earth’s weather to reach the stratosphere, the calm, dry zone above. As reflective particles spread through the stratosphere, they cause a small spurt of global cooling. But when the troposphere warms, it expands in height, eventually putting the stratosphere out of reach for these eruptions.

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View the study