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Ancient Climate Seesaw

Scientists have unravelled the complex ocean and atmospheric behaviour that caused the global climate to see-saw rapidly coming out of the most recent ice age.

The abrupt changes to the global climate 14,700 years ago caused Antarctica to suddenly stop warming and cool down for around 1500 years while the Northern Hemisphere warmed rapidly.

“Forcing the climate system into a different state can trigger climate variations that can spread globally, as seen during the warming out of the last ice age,” said team member Claire Krause of The Australian National University.

“This abrupt climate change unfolded very differently around the planet due to complicated interactions between the ocean and atmosphere. In some places in the Northern Hemisphere, the temperature jumped 10°C in the space of a few decades.”

This understanding of how the climate can change so rapidly will give us insights into whether similar events could be lurking in the future.

The research, published in Nature Geoscience (tinyurl.com/p9y6f8p), assembled 84 climate records from all over the Southern Hemisphere, spanning Antarctic ice cores, northern Australian cave records and fossilised rodent urine from southern Africa. “The project brought together a lot of seemingly separate data, and turned them into one story that is much more useful for our understanding of climate,” Krause said.

Previous studies had focused on the more numerous Northern Hemisphere records, and found opposing trends between the two hemispheres due to the behaviour of ocean currents ferrying heat northwards. However, the team found that the pattern was complicated by atmospheric circulation compensating for the ocean’s heat transport.

In the sub-tropics, atmosphere effects dominate, leading to abrupt drying and warming. However, in the South Atlantic, the Southern Ocean, New Zealand and Patagonia, the ocean drives cooling that is amplified around Antarctica by expanding sea-ice.

The resulting complex pattern of climate variations during this period in the Earth’s history had never previously been brought together in one study and understood in such detail.