So we got the general picture, that after the Mesozoic, the continents drifted apart and the oceans became more efficient heat pumps. As well, the large carbon-water cycle stopped pumping out. It got colder and colder, and not at all friendly to dinosaurs. At some perfect separation, perhaps exactly equal for the Atlantic and Pacific, the Earth could completely freeze over again. Something to think about in a few million years.
For now, we live on an Earth that is cooling on the multi-million year timescale. At some point, a few million years ago, we started continental glaciation, the true Ice Age. As I have said, the oldest evidence is 2.5 million years old, but I'll bet they keep finding older evidence. The ice advances have a tendency to erase the evidence of older advances.
Technically, we are now in the Ice Age, but that term is reserved for ice advance. During that time, we have sheets kilometres thick over poor Toronto. But the tropics don't give a shit. They go on with their happy life, drinking Pina Coladas.
During the height of the Global Warming Induced Panic, I made fun of their use of unending exponential positive feedback. If carbon dioxide really would be like that, we'd be a baked husk a long time ago. The melting of the Arctic is not positive feedback, because the place is so good at radiating heat out into Space.
But there is one positive feedback cycle that is invoked during an Ice Age. It is the most dangerous of all, except for one little saving grace of physics. But first things first. Even though we are slowly freezing to death, as the heat pump proceeds to be more efficient, there are these 10,000 year cycles of Scotch on the Rocks.
Here's what happens: The Polar Highlands are at their top elevation, with breathtaking views. All of a sudden, the N-S heat pipe (ocean currents) takes a chaotic hissy fit, perhaps something every few thousand years. This is something that is magnificent in Chaos Theory. For example, if you have the Chaotic Whirling Balls on your desk, you will notice a long-term pattern, and suddenly the whole thing stops and does something else. Our Magnetic Dynamo, in the Upper Core, does the same thing, when the Earth's Magnetic Field suddenly stops and reverses. Apparently, a big snooze for mankind.
But this oceanic reversal is no big snooze. The Pole become cold, and snow doesn't melt in the summer. Now is the summer of our discontent. :) This is exponential feedback, since the Poles are now white, and solar input is cut down. The snow builds, and oceans drop. The ocean currents are really screwed. The whole Trade Winds Mechanism shuts down. Ice builds up.
You and I would not be talking if that was all she wrote. Kilometres of ice push down the continents like a sponge ball. Yahoo! The ocean floods in, and the ice warms due to the lower elevation. Warmth is restored and we have our average cold winters. This is called an Interglacial, and sometimes it really swings the other way. Toronto becomes Florida! But not now, sheesh.
So, during Interglacials, we have the oceanic reverse, but it doesn't turn into continental glaciation because the continents are down. This most likely happened during the Little Ice Age. We might have more of those, we might have warm periods, but no Ice Age. Don't buy electric blanket stocks!
Appendix: As a thought experiment, think of a planet that is pure uniform water. And think of a planet that is pure uniform continent. What are the circulation patterns? Lots of examples in Outer Space.
Appendix2: Note the continents turn the heat pump N-S.