Bring the discussion of a couple of days ago further forward, here is a very interesting graphic from Ravelo and Ward  showing the transition from Pliocene to the Pleistocene (read R to L), which gives a somewhat different perspective on the Pleistocene than just looking at the Vostok core back to 800K (although that’s interesting as well).
Figure 1. Ravelo and Ward Figure 1 with original caption.
In the Pliocene warm period, trees grew in high polar latitudes (e.g. Banks Island, Canadian Arctic Archipelago and the north coast of Greenland – both of which I posted on previously.) Again, it’s important to note that these fossils did not get to polar latitudes by continental drift, but were found there.
Ravelo and Ward show that tropical oceans were also warmer than in the Pleistocene. It’s interesting that the variations in the Pliocene on a millennial/10-millennial scale were much smaller than in the Pleistocene.
It’s also interesting to note that the depth of the most recent ice age (ending ~17/12,000 years ago depending on location) is the deepest in this record, which, in turn, would probably make it the deepest in the entire 50 million year Tertiary period. I’m not aware of any very convincing explanations for this. In passing, some present-day changes have plausibly been attributed to ongoing rebound from the most recent Ice Age – for example, distribution of trees in western U.S.A. are not in equilibrium and are still evolving from Ice Age distributions. I’ll discuss this some time.
Mostly, it seems to me that, when you step back and look at climate history from a geological perspective, the existence of change on all scales is really quite remarkable.
What caused the transition from a Pliocene climate to a Pleistocene climate? It seems plausible that tectonic changes have something to do with it, but there doesn’t seem to be any complete consensus about which changes or how. I’ve mentioned before that the closing of the Panama Isthmus in the Pliocene seems to be related to the transition, but I’ve seen arguments that it doesn’t yield the supposed impact. I’m not convinced that the arguments are right, but the question isn’t settled. Likewise, the Himalayas rose materially during the period, which changed its properties as a barrier to the monsoon. Perhaps there were other changes. The Samoan Passage is located on an important "hot spot" and its properties would change over this period. There are surprisingly few deep channels between the Southern Ocean and the North Pacific – perhaps changes here made a difference. The Australian Plate moved northward – closing of passages in the New Guinea area were discussed by Cane et al in various articles. Which tectonic changes "matter"? I suspect that they all make some sort of difference, but there certainly doesn’t seem to be any consensus on the details of exactly how they all inter-relate; my guess is that most specialists will emphasize the importance of "their" tectonic element, but that’s just a guess.
I’m not trying to make any magisterial pronouncements here; I’m just trying to draw attention to an interesting long record of climate change.
Ravelo, A.C. and M.W. Ward, (2004). The Role of the Tropical Oceans on Global Climate During a Warm Period and a Major Climate Transition, Oceanography 14. URL