Conquering armies brought climate change

Genghis Khan may have inadvertantly brought about climate change, believes Julia Pongratz, who, with her colleagues Ken Caldeira of the Carnegie Institution and colleagues at the Max Planck Institute for Meteorology in Germany, have compared historical records with global carbon dioxide levels.

The study, published in the journal The Holocene, found that conquerors such as the Mongols, the Romans and the Vikings were able to change the climate by destroying populations and allowing the land to revert to forests. "We found that during the short events such as the Black Death and the Ming Dynasty collapse, the forest re-growth wasn't enough to overcome the emissions from decaying material in the soil," says Pongratz. "But during the longer-lasting ones like the Mongol invasion and the conquest of the Americas there was enough time for the forests to re-grow and absorb significant amounts of carbon."