New Scientist: The meteoric rise of the Incan empire between 1400 and 1532 was driven by a sustained period of warmer weather, new research on Peruvian lake sediments suggests. The sediments, from a core going back 4000 years, contain biological and organic evidence revealing sharp changes in land use and agriculture around Marcacocha, a small lake near Cuzco at the heart of the ancient empire. The higher temperatures, starting around 1150, ended thousands of years of cold aridity, and …