Volcanic eruptions outside of the tropics have a bigger effect on the planet’s climate than previously thought.
Some big eruptions spew sulfur-rich vapour high into the atmosphere, where the sulfur can form particles that reflect sunlight back into space. This cools the planet below.
Researchers have generally thought that, of all big eruptions across the planet, tropical eruptions have the strongest impact on climate, because atmospheric circulation can easily spread sulfur particles from those events. But eruptions outside the tropics can be important; for example, an unknown volcano that erupted around AD 536 caused an extreme and prolonged cold snap.
Matthew Toohey of the GEOMAR Helmholtz Centre for Ocean Research in Kiel, Germany, and his colleagues examined tree rings and ice cores that preserved information about the years 750 to 2000, to understand when the planet cooled and how much volcanic sulfur was in the air each time. Assuming that each eruption injected the same amount of sulfur at the same height in the atmosphere, eruptions outside of the tropics triggered relatively more cooling of Earth’s temperature than tropical eruptions did.