A study alleges that millions of indigenous Americans died following the arrival of Christopher Columbus in North America in 1492, and this drastic depopulation resulted in substantial global cooling.

The study, conducted by researchers from University College London and published in the journal Quarternary Science Reviews, claims that the deaths induced by European colonists occurred on such a large scale that they led to a “Little Ice Age,” a period of global cooling between the 16th and mid-19th century.

The researchers propose that some 90 percent of the indigenous population, or nearly 55 million people, died at the hands of the colonists, either through violence and or diseases like smallpox, measles, and influenza, hitherto unknown in the New World.

After the rapid drop in population, large areas of vegetation and farmland were abandoned and the resulting growth of trees and flora began absorbing more carbon dioxide and keeping it locked in the soil, causing the earth’s average temperature to fall by 0.15 degrees Celsius, the report claims.

“Humans altered the climate already before the burning of fossil fuels had started,” said Alexander Koch, a doctoral candidate in Physical Geography and the lead author of the study. “Fossil fuel burning then turned up the dial.”

The study alleges that human activity at the time “caused a drop in atmospheric CO₂ that cooled the planet long before human civilization was concerned with the idea of climate change.”

Mr. Koch was quick to insist that despite the drop in global temperatures caused by these deaths, he was not advocating killing people as a means to combat global warming.

“Killing people is not the way to go for tackling our present-day problems,” Koch said. “We need to cut down our fossil fuel emissions and not by killing people.”

The authors of the study also admit that it is notoriously difficult to quantify how many indigenous American peoples died at the time, in part because no census data or population records exist.

Neither of the metrics typically employed to approximate population numbers — European eyewitness accounts and records of encomienda payments collected during colonial rule — can be relied on for accurate figures, the study acknowledges.

For their new study, researchers summed up estimates of pre-Columbian populations in 119 regions of North and South America, leading to their figure of about 60.5 million people living in the Americas prior to the arrival of Europeans.

The new study and its explanation of the Little Ice Age as a product of human activity has met with some opposition.

“It is a highly interesting paper,” said Joerg Schaefer from the Lamont-Doherty Earth Observatory of Columbia University, especially because it will trigger controversy and further research.

Nonethless, the researchers “are likely overstating their case,” Schaefer said. “I am absolutely sure this paper does not explain the cause of the carbon dioxide change and the temperature change during that time.”

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