He walks through the evidence showing sea levels were higher during the climatic optimum than they are today. Then came the cooling, the neoglacial period when glaciers grew and fluctuated around a mean before plunging again around 1300 years ago into the Little Ice Age. That cooling was significant, measurably colder than present conditions. What did a couple of degrees of cooling mean for human civilization during that period? The implications are worth examining in detail. The historical record shows us that climate variability is not a modern invention, it is the norm across the Holocene, and understanding these natural cycles gives us context for evaluating what we see today.