LOL!!!!
Explain how the earlier ice age happened.
Simple. There were no internal combustion engines. Muscle cars were the only thing staving off the return of the ICE AGE. We are doomed unless we bring back the 442 and GTO. We must manufacture millions of them and get the lead back in the gas.
Which one? There were several Ice Ages including the one we are in now. The current Ice age started about 2.5 million years ago (scores of glacial advances) maybe caused by the closure of the Isthmus of Panama.