No Gotmuddy, episodes of mountain building, volcanism, and other factors played a role- factors which don't explain the climate shift we're currently experiencing.
The one that does is pretty simple: the CO2 present in the Miocene atmosphere was eventually sequestered in formations of coal, natural gas, oil, peat, limestone, fossilized dino turds, and other carbon-bearing deposits. The reduction in atmospheric CO2 brought more moderate global temperatures- the climate our species adapted to. The stuff wasn't interacting with our atmosphere, until we dug it up and started burning it. The same chemical compound then seems to be the culprit today, how it's getting into the atmosphere makes no difference.
While it's all well and good that Greenland was warm 15 million years ago, we're only adapted to the climate of the last 200,000 years or so. We don't know what an ice-free Greenland means for our species, we don't know how it affects trade, agriculture, geopolitics....we don't know what it means for habitated areas such as sub-Saharan Africa, central Asia, Australia, the American Southwest, or even Missouri. But if we look at recent history- drought and wildfires in Russia which reduced grain exports to the Middle East, and subsequent food riots which sparked the Arab Spring- it likely won't be pretty.
Point is, I guess, it's about more than polar bears and cow farts.