LOL!!!
What happened to North America 30-50 million years ago is happening to Greenland now. That you and YOUR SIDE cannot explain it is absolute proof your side has NO CLUE at all. That Greenland froze while North America thawed proved Sun and Atmosphere are not the cause.
Continent specific ice ages. Why continent specific? What causes ice ages?
An ice age like Greenland begins when land gets to within 600 miles to an Earth pole. There the annual snowfall ceases to fully melt in the "summer" and hence starts to STACK. That is the start of an ICE AGE which is continent specific because both ice ages of today, Greenland and Antarctica, demonstrate that ice does not grow out over ocean, it breaks off. Your side laughably calls that "melting" but in reality the H2O is still solid form - LOL...
A continent specific ice age has parameters, and Greenland's data is the best we have. Speed - 1 mile every thousand years.
Greenland and North America are both moving on the same vector on a sphere, pushed there by the fault in the center of the Atlantic floor.
The North American plate is moving to the west-southwest at
about 2.3 cm (~1 inch) per year driven by the spreading center that created the Atlantic Ocean, the Mid Atlantic Ridge.
Greenland will eventually follow NA SW, but has not yet reached its "closest to the pole" point, so it is still moving NW and has for tens of millions of years. The angle of the fault in the North Atlantic is SW-NE which pushes Europe SE (why all of Europe's glaciers are melting and have for millions of years) and Greenland NW (pushed straight into that 600 mile zone = ice age)
Ice ages push glaciers right out of a polar circle. Did on NA, and are doing so both on AA and Greenland. AA's ice age is 40+ million years old.
So that is 99% of Earth climate change = WHERE LAND IS.
Earth with two polar oceans = no ice
Earth with two Antarcticas = twice the ice
Greenland froze because it entered the 600 mile zone, while NA thawed because, other than Ellesmere Island, it is now out of the 600 mile zone.