Genghis Khan Killed So Many People It Actually Cooled the Earth
Genghis Khan's conquests killed an estimated 40 million people, causing so much farmland to return to forest that it removed 700 million tons of CO2 from the atmosphere.
About this fact
A 2011 study by the Carnegie Institution found that Genghis Khan's conquests in the 13th century had an unexpected environmental impact. The Mongol invasions killed an estimated 40 million people - roughly 11% of the world's population at the time. This massive depopulation caused vast areas of cultivated land to be abandoned and return to forest. The reforestation removed approximately 700 million tons of carbon dioxide from the atmosphere, equivalent to the annual output of the entire global gasoline industry today. This represents one of the first instances in history where human activity caused global cooling rather than warming. The study suggests that the Mongol conquests may have been one of the first man-made climate changes on a global scale.