Holiday glaciations

In honor of the holidays, let's talk about the North (and South) Pole!

Santa realises that CO₂ plays an important role in the climate
 of his home. Source: Skeptical Science

We have seen that the Earth has suffered many changes along its history, and Antarctica and the Arctic are no exception. Starting from the fact that Antarctica was not always in the same place - it has been in the polar latitudes of the southern hemisphere only since the Cretaceous. And even when it reached this location, it was warm (DeConto & Pollard, 2003). It was around 34 million years ago at the Eocene-Oligocene boundary, that the ice sheets started covering the continent to about 50% of present day ice (Zachos et al., 2001). The likely cause was a decline in CO₂ levels in combination with favourable periods of the orbital cycles and ice albedo feedback, as DeConto & Pollard  (2003) found in their modelling results. 

The ice covered Arctic is much more recent, with the glaciation occurring 10 million years ago at the earliest, though it was not until 2.55 million years ago that there were "significant ice sheets". In this case the cooling was driven in part by lower CO₂ levels caused by tectonic changes. The uplift of the Himalayas would have increased the chemical weathering and in consequence drawing down more CO₂ than before. However, the orbital forcing played an important role for the intensification of the glaciation. Between 3.2 - 2.4 million years ago, the orbital forcing promoted cooler summers in the Northern Hemisphere, which allowed the ice sheet to grow rapidly (Maslin et al., 1998).