The BBC has a post about the effect of the colonization of America on the environment.  A study by scientists from the University College London, UK claim that the colonization at the end of the 15th century killed so many native Americans, it disturbed Earth’s climate.  The paper by Alexander Koch and colleagues was published in Quaternary Science Reviews.

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.

This pulled down enough carbon dioxide (CO₂) from the atmosphere to eventually chill the planet.

It’s a cooling period often referred to in the history books as the “Little Ice Age” – a time when winters in Europe would see the Thames in London regularly freeze over.

“The Great Dying of the Indigenous Peoples of the Americas led to the abandonment of enough cleared land that the resulting terrestrial carbon uptake had a detectable impact on both atmospheric CO₂ and global surface air temperatures,”

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.

It then assessed how the numbers changed in following decades as the continents were ravaged by introduced disease (smallpox, measles, etc), warfare, slavery and societal collapse.

It’s the UCL group’s estimate that 60 million people were living across the Americas at the end of the 15th Century (about 10% of the world’s total population), and that this was reduced to just five or six million within a hundred years.

The scientists calculated how much land previously cultivated by indigenous civilisations would have fallen into disuse, and what the impact would be if this ground was then repossessed by forest and savannah.

The area is in the order of 56 million hectares, close in size to a country like modern France.