Palaeogeog. Palaeoclim. Palaeocean. (2013)


During the Pliocene warm period 3 million years ago, Arctic temperatures were 10–12 °C warmer than today, far greater than the mean global temperature difference of only 2–4 °C. This polar amplification could be related to the loss of sea ice in the Arctic Ocean, according to model simulations.

Ashley Ballantyne of the University of Montana, USA, and colleagues used an atmosphere–ocean general circulation model to assess the role of sea ice in Arctic temperatures during the Pliocene warm period, when atmospheric CO2 concentrations were similar to today. Their simulations without sea-ice formation in the Arctic Ocean best matched proxy-based temperature reconstructions for the high northern latitudes. In these simulations, the lack of sea ice promoted atmospheric convection over the ocean, increasing atmospheric water vapour content and cloud formation. Moreover, these simulations also showed a reduction in seasonal temperature variations in the Arctic, consistent with some observational data.

The researchers note that their ice-free simulation slightly overestimates the temperature response relative to the proxy reconstructions, suggesting that Arctic climate patterns during the mid-Pliocene may be best explained by the loss of most, but not all, winter sea ice.