Scientists from the University of New South Wales have found an ancient kauri tree in New Zealand that holds the key to the cause of rising Arctic temperatures.

The 30,000-year-old kauri tree in a peat swamp in New Zealand showed a new mechanism that could explain how temperatures in the Northern Hemisphere spiked several degrees centigrade within a few decades during the last global ice age.

Significant, rapid warming spikes during glacial periods are known as Dansgaard-Oeschger events and are linked to a phenomenon known as bipolar seesaw where increasing temperatures in the Arctic simultaneously occur as cooling occurs over the Antarctic and conversely.

Previously, it was thought the divergences in temperature at opposite poles were driven by changes in the North Atlantic causing deep ocean currents -- referred to as the ocean conveyor belt -- to shut down leading to warming in the Northern Hemisphere and cooling in the Southern Hemisphere.

The study, published Tuesday in Nature Communications, used a detailed sequence of radiocarbon dates from an ancient New Zealand kauri tree to precisely align ice, marine and sediment records over a period of great climate change.

"Intriguingly, we found that the spike in temperature preserved in the Greenland ice core corresponded with a 400-year-long surface cooling period in the Southern Ocean and a major retreat of Antarctic ice," professor Chris Turney, UNSW scientist, said in a press release.

"As we looked more closely for the cause of this opposite response we found that there were no changes to the global ocean circulation during the Antarctic cooling event that could explain the warming in the North Atlantic. There had to be another cause."

Researchers turned to examining lake sediments from the Atherton Tableland in Queensland and found sediments exhibiting a simultaneous collapse of rain-bearing trade winds over tropical northeast Australia.

They then analyzed climate models showing the release of large volumes of freshwater into the Southern Ocean and found there was cooling in the Southern Ocean but no change in the global ocean circulation.

Researchers also found that the freshwater pulse caused rapid warming in the tropical Pacific, which led to changes to the atmospheric circulation that triggered sharply higher temperatures over the North Atlantic and the collapse of rain-bearing winds over tropical Australia.

"Our study shows just how important Antarctica's ice is to the climate of the rest of the world and reveals how rapid melting of the ice here can affect us all. This is something we need to be acutely aware of in a warming world," Turney said.

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Sea ice in the Arctic Ocean is in a downward spiral, with summer minimum extents about 40 percent smaller than in the 1980s. But predicting how the sea ice is going to behave in a particular year is tricky: There are still many unknowns about the conditions of the sea ice cover, to say nothing of the difficulties of forecasting weather and ocean behavior over seasonal timescales. NASA rese ... read more

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