A new paper from researchers at University College London argues that the genocide of indigenous peoples in the Americans after Columbus’s landing in 1492 had a significant effect on the Earth’s global climate and was a major cause of the Little Ice Age, the dip in global temperatures from the 16th to the 19th centuries. They estimate that 55 million indigenous people died during Europe’s conquest of the Americas (~90% of the population), and the 56 million hectares of land that they had cleared of vegetation (roughly the area of Kenya) was then reclaimed by forests, which then took in more carbon dioxide, reduced the greenhouse effect, and caused the Earth to cool. From the paper’s conclusion:

We calculate that this led to an additional 7.4 Pg C being removed from the atmosphere and stored on the land surface in the 1500s. This was a change from the 1400s of 9.9 Pg C (5 ppm CO2). Including feedback processes this contributed between 47% and 67% of the 15-22 Pg C (7-10 ppm CO2) decline in atmospheric CO2 between 1520 CE and 1610 CE seen in Antarctic ice core records. These changes show that the Great Dying of the Indigenous Peoples of the Americas is necessary for a parsimonious explanation of the anomalous decrease in atmospheric CO2 at that time and the resulting decline in global surface air temperatures.

The authors also assert that this effect of human action on global climate marks the beginning of the Anthropocene epoch.

I first heard about this theory from Charles Mann’s excellent 1493, which led me to William Ruddiman’s 2003 paper. I heard about this most recent study from Mann too… he called it “most careful study of the impacts of Euro conquest of Americas I’ve yet seen”.

If you’re not up for reading the paper itself, you can check out the coverage from the BBC, the Guardian, Nature, or the NY Times.