The arrival of Europeans in the Americas didn't just kill off millions of people—it may have also helped trigger the Little Ice Age, CNN reports. A new study says so many indigenous people died of disease or slaughter in the "Great Dying" after 1492 that far less agricultural land was used, causing trees and vegetation to rise up and suck more carbon dioxide from the atmosphere. "CO2 and climate had been relatively stable until this point," says co-author and University College of London Professor Mark Maslin. "So, this is the first major change we see in the Earth's greenhouse gases." Until now, some scientists said the period of cooling between the 1600s and the 1800s known as the Little Ice Age was caused only by natural processes like volcanic eruptions.
The study mixes historical data, archaeology, and carbon analysis of Antarctic ice to make its case. Noting that roughly 56 million indigenous people died in North, Central, and South America in the century following first contact, the authors say vegetation and trees sprouted up in an area equivalent to France, massively lowering the atmosphere's CO2 level. Analysis of Arctic ice appears to corroborate this by revealing a bigger CO2 dip than usual in 1610. "What’s interesting is that we can see natural processes giving a bit of cooling," Maslin tells the Telegraph, "but to actually get the full cooling—double the natural processes—you have to have this genocide-generated drop in CO2." (Meanwhile, scientists have found a culprit in starfish devastation.)