Frozen Earth: The Planet Got Warm After Frequent Volcano Eruptions Melted the Last Ice Age

Volcanic eruptions may have sped up the end of the last ice age. Halldor Kolbeins/AFP/Getty Images

Fire melts ice, but so does ash: Dark particles settling onto white ice make the surface trap more heat, the same way wearing a black shirt on a sunny day is hotter than wearing a white shirt. And scientists have seen the connection play out in real time across Earth's surface as volcanic eruptions have scattered ash on snow and made it melt faster. But for the first time, a team of researchers has pinpointed the phenomenon in the distant past, as they report in a new article published in the journal Nature Communications.

"The paper is the first to document that this phenomenon likely also occurred during the last deglaciation, and raises interesting questions regarding the role of volcanism on deglaciation," James Baldini, an Earth scientist at Durham University in the U.K. not affiliated with the study wrote Newsweek in an email.

He notes that traditionally, scientists thinking about the impact of volcanoes on climate focus on tiny particles called aerosols, which are released during eruptions, form clouds that block sunlight and keep the Earth cooler. This paper, on the other hand, suggests that effect might have been balanced out by melting ice—leaving the planet no cooler than it was before.

The team used an unusual form of evidence: glacial varves, or the layers of dirt and mud deposited each year beneath a glacier. Just like the rings of new wood trees grow every year in a light-dark pattern, glaciers annually deposit first a wide lighter layer of sandier soil during the summer, then a narrower layer of darker clay during the winter. The thickness of each layer lets scientists calculate how much the glacier in question melted, since the more a glacier melts the more sediment it carries away.

Volcanic eruptions scatter ash and dust on ice sheets, making them melt faster. Halldor Kolbeins/AFP/Getty Images

For this study, the scientists looked at varves found in what was once the Baltic Ice Lake, now part of the eastern Baltic Sea. They focused on a section corresponding to between 13,200 and 12,300 years ago—the very beginning of the end of the last ice age, when the giant ice sheets that had covered Earth began melting away.

They paired that glacial history with ice core records that allowed them to study volcanic eruptions during the same period. Specifically, they used an ice core pulled out of Greenland in 1993 that is particularly good at catching evidence of Icelandic eruptions by letting scientists measure sulfate, a chemical released by volcanoes.

The researchers found not only that volcanoes in Iceland were erupting 50 times more often than they do now, but that spikes in eruptions corresponded to spikes in varve thickness—suggesting that the connection between volcanic ash and melting ice sheets held just as true thousands of years ago as it does today.