European settlers killed 56 million indigenous people over about 100 years in South, Central and North America, causing large swaths of farmland to be abandoned and reforested, researchers at University College London, or UCL, estimate. The increase in trees and vegetation across an area the size of France resulted in a massive decrease in carbon dioxide (CO2) in the atmosphere, according to the study.
Carbon levels changed enough to cool the Earth by 1610, researchers found.
…”The ice cores showed that there was a larger dip in CO2 (than usual) in 1610, which was caused by the land and not the oceans,” said Alexander Koch, lead author of the study.
A small shift in temperatures — about a 10th of a degree in the 17th century — led to colder winters, frosty summers and failing harvests, Koch said.