I’m slowly working my way through Charles Mann’s 1493 and there are interesting tidbits on almost every page. One of my favorite bits of the book so far is a possible explanation of the Little Ice Age that I hadn’t heard before put forth by William Ruddiman.

As human communities grow, Ruddiman pointed out, they open more land for farms and cut down more trees for fuel and shelter. In Europe and Asia, forests were cut down with the ax. In the Americas before [Columbus], the primary tool was fire. For weeks on end, smoke from Indian bonfires shrouded Florida, California, and the Great Plains.

Burning like this happened all over the pre-Columbian Americas, from present-day New England to Mexico to the Amazon basin to Argentina. Then the Europeans came:

Enter now the Columbian Exchange. Eurasian bacteria, viruses, and parasites sweep through the Americas, killing huge numbers of people — and unraveling the millenia-old network of human intervention. Flames subside to embers across the Western Hemisphere as Indian torches are stilled. In the forests, fire-hating trees like oak and hickory muscle aside fire-loving species like loblolly, longleaf, and slash pine, which are so dependent on regular burning that their cones will only open and release seed when exposed to flame. Animals that Indians had hunted, keeping their numbers down, suddenly flourish in great numbers. And so on.

The regular fires and forest regrowth resulted in less carbon dioxide in the atmosphere and the atmosphere traps less heat. It’s like global warming in reverse.