I accept that melted ice sheets is what raises sea level so not necessarily going to raise Co2.
Thus what caused glaciers to melt. You say stronger insolation levels. I suspect more than that. Diminishing Sunspot numbers, increasing cosmic rays. Cosmic rays are not just linear in supply. They vary as well
I think what happened then is going to happen again. Or his happening again.
I also think that the 190-280ppm you quoted are way underestimated. Ice core data is extremely low resolution. There is plenty of stomatal data that shows vast differences in Co2 between ice core an stomatal.
