some scientists believe Ice-Age climactic change happens drastically overnight, which explains why some Mammoth were discovered with fresh green flowers still in their mouths when they died. (Flash frozen)
The best explanation I've heard for that was a huge eruption that spewed dust and gas several hundred miles in the air. The cloud quickly cooled to subfreezing temperatures and then rapidly descended to freeze the Mammoth.
The current phenomenon in Antarctica where the Northern Ice Shelf is just slipping away from the Continent is due to Sublevel volcanic activity. Which further supports the "Magnetic Shift" hypothesis. There are also factual reports of major anomalies in the Earth's magnetic field within the last few years. These magnetic anomalies have caused compass errors in places previously considered as stable.
Global Warming couldn't possibly have caused it because the heat source is coming from the Earth beneath the Ice Shelf which is several thousand feet thick.