Climates began to warm, erratically, about twenty thousand years ago, and by thirteen thousand years ago, average global temperatures were similar to today. Then, during the cold snap known as the Younger Dryas period, they fell sharply for at least a thousand years, after which they rose again. For about ten thousand years, climates have been unusually stable. Warmer, wetter climates and exceptional climatic stability made farming more viable than it had been for at least one hundred thousand years, providing the Goldilocks conditions for the entire agrarian era.
