13,000 years ago, the last Ice Age was nearing its end. The kilometre-thick ice sheet covering the northern part of the world was beginning to melt, and the climate was getting warmer and warmer.
But then everything changed. The northern region experienced very rapid climate change. Within a very short time, possibly as little as a decade, temperatures in northern regions dropped dramatically around 13,000 years ago, Jostein Bakke tells Science Norway.
"It was an abrupt and sudden reversal," he says.
Bakke is a professor at the University of Bergen's Department of Earth Science and has worked extensively on past climates.
Here you can see how abrupt the estimated temperature change on the Greenland ice sheet was over the last 17,000 years. The Younger Dryas stands out dramatically.(Graph: USGS)
Ripple effects for 1,000 years
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The cold period had lasting effects for a thousand years. Ice in both North America and Scandinavia began growing again, and the ocean currents carrying warm water from the Gulf of Mexico northwards weakened.
This is called AMOC, and there are often research news stories about the possibility that this ocean circulation could weaken now as well.
If that happens, the northern part of the world could become much colder than it is today.
So something triggered this cooling event 13,000 years ago. In a new study, researchers argue that a sudden shock to the world’s climate may have helped create this climatic downturn, known scientifically as the Younger Dryas.
The researchers claim they have found evidence of extensive volcanic activity during this period at several different locations.
"I don't think it fully explains the Younger Dryas, but it could be part of the explanation. I think this looks like solid geological work," Bakke says after reading the study.
Freshwater, melting ice, and meteorites?
The reasons behind what happened are complex and debated, but a period of major volcanic eruptions that cooled the climate may have played a role.
Sediments found in caves in the United States reveal a detailed geological record spanning long periods of time, according to the study.
The researchers identified certain isotopes that may point to increased volcanic activity at the beginning of the Younger Dryas. They do not know where the eruptions occurred or how large they were.
But there may have been more volcanic eruptions than usual during a period of just over a hundred years at the beginning of this period.
Jostein Bakke notes that the study includes many strong measurements and a detailed time series, making increased volcanic activity seem likely.
Large volcanic eruptions can lower temperatures and affect the climate because they spew out particles and dust that block sunlight. This has previously had major consequences for life on Earth, including for humans, who may have experienced major societal collapses as a result of volcanic eruptions. You can read more about the Fimbulwinter theory on Science Norway.
Meltwater collects on top of a huge glacier.(Photo: Pi-Lens / Shutterstock / NTB)
Rapid change
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But it happened suddenly.
“Ice cores from Greenland indicate that it may have taken place in less than a decade,” Bakke says.
The change was so abrupt that an earlier hypothesis proposed that the Younger Dryas was caused by a major meteor impact – which in turn affected the climate.
“That hypothesis has been disproven,” he says.
The researchers point to scientific reviews showing little evidence that a meteorite impact was a major driver of the event.
Dust and ash are thrown into the atmosphere during a volcanic eruption in Papua New Guinea.(Photo: Taro Taylor / CC BY-SA 2.0)
Bakke explains that enormous amounts of meltwater from inland regions, including North America, played a key role in triggering this rapid cooling.
He adds that when freshwater flows into the North Atlantic, it can freeze and form a layer over the warm water coming northwards from the Gulf of Mexico.
"That can weaken the exchange of heat between the ocean and the atmosphere. This happened on a very large scale during the Younger Dryas because so much meltwater flowed into the ocean," he says.
Bakke believes heightened volcanic activity during this period may help explain why the Younger Dryas became both so cold and so abrupt.
