With my recent trip to Peru and on-going existence in the modern world, I found this to be an interesting article.

New research has revealed that a prolonged period of warm weather between AD1100 and 1533 cleared large areas of mountain land to be used for farming, helping the Incas to spread their influence from Colombia to the central plains of Chile.

With the tree line moving steadily higher up the mountains, the Incas carved terraces into the mountainside to grow potatoes and maize, and developed a system of canals to irrigate the land.

Incas and Climate Change