For the past 12,000 years, the earth has experienced a relatively stable climate. Today, that predictability has ended, and global warming is our new reality. Yet such shifting weather patterns threatened Homo sapiens once before, right here in North America as the continent was first being colonized. About 15,000 years ago, the weather began to warm, melting the glaciers of the Late Pleistocene and driving the beasts of the Ice Age toward extinction....

Travel back through history, over 27,000 years into the past, when Arctic glaciers reached as far south as London and people faced a daily struggle not just to survive as individuals, families or groups, but to avoid the ultimate extinction of the species. A key moment in the course of history saw the two branches of humankind, the Neanderthals and the Cro-Magnons, face off against the backdrop of perilous cold, harsh conditions, and massive predators....