Sudden drop in Antarctic Temperatures 14 million years ago

Scientists have documented what must have been a "sudden" unexplained drop in temperature 14 million years ago. Equally interesting, more recent warm temperatures were not associated with any significant melting of the polar ice sheets. Science Daily has this:

An abrupt and dramatic climate cooling of 8 degrees Celsius, over a relatively brief period of geological time roughly 14 million years ago, forced the extinction of tundra plants and insects and transformed the interior of Antarctica into a perpetual deep-freeze from which it has never emerged. . . .

The mean summertime temperatures would have dropped in that period by as much as 8 degrees Celsius. On average, the summertime temperatures in the Valleys during this temperate period would have been as much as 17 degrees warmer than the present-day average. What caused the change, Marchant said, "Is really a big unknown", though theories abound and include phenomena as different as the levels of carbon dioxide in the atmosphere and tectonic shifts that affected ocean circulation. . . .

This conclusion suggests that even when global atmospheric temperatures were warmer than they are now, as occurred--approximately 3.5 million years ago during the Pliocene Epoch--and as might occur in the near future as a consequence of global warming, there was no significant melting of the East Antarctic ice sheet inland of the Dry Valleys, nor were there dramatic changes in environmental conditions in the fossil region.