Colonisation of the Americas at the end of the 15th Century killed so many people, it disturbed Earth's climate.
"The team says the disruption that followed European settlement led to a huge swathe of abandoned agricultural land being reclaimed by fast-growing trees and other vegetation."
"The team reviewed all the population data it could find on how many people were living in the Americas prior to first contact with Europeans in 1492."
Population estimates range from 2 million to 100 million. None of them are based on hard, solid facts.