The Greenland ice core data shows that the earth started warming out of the last major ice age, just past 15K years ago, and then quickly went back into ice age for a couple thousand years, warmed up again around 12 or 13K years ago and converged to an extremely stable temperature cycle that has lasted until the present time. Today, we are still in that stable range.
Antarctic Ice Core Data showed that Earth started warming 20K years ago and Greenland Ice Core Data showed 15K years ago. Both are right. The warm oceans flowed around Antarctic, removing ice shelves before the oceans were high enough to enter the Arctic and do the same around Greenland.
