One -possible- different past. Of course, we may be wrong about what caused it to be much warmer -in Greenland- -at that time- .

One simpler example: the Earth's North polar axis may once have farther from Greenland. Plate tectonics has made this a much different planet than it was 200Million or 400M or 600M years ago, and there was possibly a time when Greenland was much farther from the pole ... and had no ice.

Or (if Charles Hapgood was right), much of the Earth's crust may have shifted it's position (think an orange-skin no longer firmly attached to the orange) over, say, 100,000 years or so.