Loss of Arctic sea ice could release the ocean’s heat and greatly alter the Arctic climate, just as it did 3 million years ago, new research from the University of Montana has found.

Coauthored by UM bioclimatology professor Ashley Ballantyne, the five-year study found that when Arctic sea ice is removed, heat lost from the ocean warms the interior land.

“The ocean is a huge heat source,” Ballantyne said Tuesday. “If you lose the sea ice in the summer and it doesn’t advance back in the winter, you lose the heat from the ocean and it amplifies the trend.”

Ballantyne said the trend has occurred in the past, when surface temperatures in the Arctic were nearly 68 degrees warmer (20 degrees Celsius) than today’s surface temperatures.

Back then, during the Pliocene Epoch, the warmer surface temperatures likely were caused by the Arctic’s ice-free condition.

Ballantyne said concentrations of carbon dioxide in the atmosphere have reached 400 parts per million for the first time since the height of the Pliocene.

“This suggests that atmospheric C02 concentrations of 400 ppm may be sufficient to greatly reduce the seasonal persistence of Arctic sea ice,” Ballantyne said.

The findings are relevant to today’s atmospheric models and what, exactly, a loss of sea ice means to both sea and land temperatures.

Ballantyne said the extent of Arctic sea ice and its seasonal distribution could alter the Arctic’s overall climate.

The impacts also may extend beyond the Arctic Ocean, holding implications for the future of the Arctic system.

“You go back 3 million years to the Pliocene when temperatures were 15-20 degrees (Celsius) warmer and the land was covered by an arboreal forest,” Ballantyne said. “You dig into the permafrost and you find these layers of perfectly preserved forest. We can pull perfectly preserved larch trunks out of this permafrost.”

Northwestern University, the University of Colorado and the National Center for Atmospheric Research also contributed to the study.

The research was published in the July issue of Nature Geoscience. The full paper will appear in “Palaeogeography, Palaeoclimatology, Palaeoecology: An International Journal for the Geosciences.”

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