Arctic sea ice during the Pliocene era

Ballantyne and coauthors from Northwestern University, the University of Colorado and the National Center for Atmospheric Research used a global climate model to investigate the amplification of Arctic temperatures in Earth's past.

Atmospheric carbon dioxide concentrations recently reached 400 parts per million for the first time since the Pilocene Epoch, three million years ago. During this era, Arctic surface temperatures were 15-20 degrees Celsius warmer than today's surface temperatures.

Ballantyne's findings suggest that much of the surface warming likely was due to ice-free conditions in the Arctic. That finding matches estimates of land temperatures in the Arctic during the same time. This suggests that atmospheric carbon dioxide concentrations of 400 ppm may be sufficient to greatly reduce the spatial extent and seasonal persistence of Arctic sea ice.

The authors also found that surface temperatures in the Arctic are more sensitive to the amount of sea ice than to the amount of land-based ice. They show that once sea ice is removed, heat lost from the ocean recirculates in the atmosphere and warms the interior land.

The findings are relevant to modern-day atmospheric models and to an understanding of what a loss of sea ice means to both sea and land temperatures.

According to the findings, the extent of Arctic sea ice and its seasonal distribution clearly have broad impacts on Arctic climate that extend beyond the Arctic Ocean itself and have important implications for the future of the Arctic system.