It is quite regularly pointed out – by Steve Bloom and others – that the Pliocene (5 – 3 million years ago) is quite interesting since the temperatures were 2 – 3oC higher than today, sea levels were 20 – 25m higher than today, yet CO2 levels were about the same as today (400ppm). As I understand it, however, it’s never been clear why sea levels could be so much higher than today, since it would require a significant retreat of the East Antarctic Ice Sheet (EAIS) and this is something that models have not been able to simulate.
A recent paper by Pollard, DeConto and Alley (Potential Antarctic Ice Sheet retreat driven by hydrofracturing and ice cliff failure, however, has tried to address this issue. What this study suggests is that floating ice shelves may be drastically reduced or removed completely by increased oceanic melting, and by hydrofracturing due to surface melt draining into crevasses. As I understand it, increased oceanic melting causes cliff failure.
The maps showing the retreat of the EASI are shown below. As one might expect, even though this process could explain the sea level rise during the Pliocene, it still took 1000s of years.
Maybe the more interesting figure is the one on the right which shows how sea level rises if cliff failure and hydrofracture are included or not. As illustrated in the maps above, the overall sea level rise takes 1000s of years. However, as the paper says, ice-sheet model accelerates the expected collapse of the West Antarctic Ice Sheet to decadal time scales. So, not only can the sea level rise during the Pliocene be explained by cliff failure and hydrofracture, these processes could also result in a rapid initial rise in sea levels due to the collapse of the West Antarctic Ice Sheet (WAIS).
Anyway, that’s all I was going to say. This is not really my area of expertise, so I’m mainly posting this because it seems interesting and in the hope that I might learn more from those who choose to comment.