European contact killed so many Indians who changed the climate, study says


Prior to the arrival of Columbus in the Americas in 1492, the area had prosperous indigenous populations, totaling more than 60 million people.

Just over a century later, that number dropped to close to 6 million.

European contact brought with it not only war and famine but also diseases such as smallpox that decimated local populations.

Now, a new study published in the journal Quaternary Science Review argues that these deaths occurred on such a scale that they led to a "Little Ice Age": an era of global cooling between the 16th and the 19th centuries.

Researchers at University College London found that after rapid population decline, large areas of vegetation and agricultural land were abandoned.

The trees and flora that repopulated that unmanaged land began to absorb more carbon dioxide and keep it trapped in the soil, removing as much greenhouse gas from the atmosphere as the planet's average temperature dropped by 0.15 degrees Celsius.

Normally, experts consider the Industrial Revolution as the genesis of man-made climate impacts. But this study shows that the effects may have started about 250 years earlier.

"Humans have altered the climate already before the start of the burning of fossil fuels," lead study author Alexander Koch told Business Insider. "Fossil fuel burning turned on the dial."

More than 50 million indigenous people died in 1600

Experts have long struggled to quantify the extent of the slaughter of Native Americans in North, Central and South America. This is mainly because there are no census data or population size records to help identify how many people were living in those areas before 1492.

To approximate population numbers, researchers often rely on a combination of European eyewitness accounts and records of payments of "encomienda" taxes created during colonial rule.

But none of the metrics is accurate – the former tends to overestimate the size of the population, as early settlers wanted to announce newly discovered land riches to European financiers.

The second reflects a payment system that was put into place after many disease outbreaks had already run, the authors of the new study note.

Thus, the new study offers a different method: the researchers divided North and South America into 119 regions and examined all published estimates of pre-Columbian populations in each region.

In doing so, the authors estimated that about 60.5 million people lived in the Americas before European contact.

After Koch and his colleagues gathered the numbers before and after, the conclusion was glaring. Between 1492 and 1600, 90 percent of indigenous populations in the Americas had died.

That means that about 55 million people have died from violence and unprecedented pathogens such as smallpox, measles and influenza.

According to these new calculations, the death toll represented about 10% of Earth's population at the time. They are more people than the modern populations of New York, London, Paris, Tokyo and Beijing combined.

The disappearance of so many people meant less agriculture

Using these population numbers and estimates of the amount of land used per capita, the study authors estimated that indigenous people grew about 62 million hectares (239,000 square miles) of land before European contact.

That number also dropped about 90 percent to just 6 million hectares (16,000 square miles) in 1600.

Over time, the trees and vegetation took over the previously cultivated land and began to absorb more carbon dioxide from the atmosphere.

Carbon dioxide captures heat in the planet's atmosphere (this is what human activity now emits on an unprecedented scale), but plants and trees absorb it as part of photosynthesis.

So when the land previously cultivated in North and South America – equal to an area almost the size of France – was reforested by trees and flora, atmospheric levels of carbon dioxide fell.

Antarctic ice cores dating from the late 1500s and 1600s confirm the decrease in carbon dioxide.

This drop in CO2 was enough to lower global temperatures by 0.15 degrees Celsius and contribute to the enigmatic global cooling trend called the "Little Ice Age", during which the glaciers expanded.

Persistent questions

"Researchers are probably overstating their case," Joerg Schaefer, Earth's Earth science expert, Lamerg-Doherty Earth of Columbia University, told Live Science.

"I am absolutely certain that this article does not explain the cause of the change in carbon dioxide and the change in temperature during that period."

Koch said part of the fall in carbon dioxide may have been caused by other natural factors such as volcanic eruptions or changes in solar activity.

But he and his colleagues concluded that the death of 55 million Native Americans explained about 50 percent of the overall reduction in atmospheric carbon dioxide.

"So you need natural and human forces to explain the fall," he said.

Koch said the findings revise our understanding of how long human activity has influenced the Earth's climate.

"Human actions at the time caused a drop in atmospheric CO2 that cooled the planet long before human civilization cared about the idea of ​​climate change," he and his co-authors wrote.

But they warned that if a similar reforestation event happens today, it would not help much to mitigate the current rate of global warming.

The drop in atmospheric carbon dioxide that occurred in 1600 represents only about three years of fossil fuel emissions today, Koch said.

"There is no way to reduce emissions of fossil fuels," he said, adding that reforestation and forest restoration also remain crucial.

This article was originally published by Business Insider.

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