A new study documents the global cost of colonialism. Why does it matter? Because the invasion of the Americas changed everything on the planet. There was a death rate of more than 90 percent of the people, now labeled "depopulation" in a scientific report. At that time, the Indigenous population of the Americas was 10 percent of the world's population and home to the largest and most complex cities.

The study also raises new questions, the impact of humans on nature? And what that might mean for climate change policy in the decades ahead?