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The last time humans engineered the climate, they changed history

Illustration: Aïda Amer/Axios

Forecasts of a grim future ahead from extreme weather have been at once so vague and frequent as to numb many people as to what's coming. But it turns out that this is the second incidence in history of climate change at least partly induced by humans.

Driving the news: In the first, a half-millennium ago, humans made the Earth cooler, which contributed to famine, disease, and popular uprisings in Europe, experts say. In much-discussed new research, U.K. scientists say the 16th century exploration of the Americas by Europeans led to a cascade of disaster.

The toll included:

  • The deaths of some 55 million native people to pandemic disease over less than a century, representing 90% of the inhabitants of North and South America — and 10% of the world population.
  • A reforestation of their now-fallow farms, covering a combined area about the size of France, causing a massive and sustained amount of carbon to be sucked from the atmosphere.
  • A consequent deepening of the so-called Little Ice Age, when temperatures plunged in Europe and across the globe. Among popular uprisings were mob violence in Ireland and a resurgence of witchcraft trials.

Why it matters: The research, from four scholars at University College London, suggests that European contact with the Americas starting with Columbus had an impact on a vast scale — shifting human and Earth history.

"It caused about half of the cold snap in the 17th century that caused all kinds of havoc all over the world," Charles Mann, author of "1493: Uncovering the New World that Columbus Created," tells Axios.

  • Thought bubble from Andrew Freedman, author of Axios' Science newsletter: "Assuming the new study is correct, it indicates that the era of human-engineering of the climate system started much earlier than the Industrial Revolution."
  • "It also suggests that the discussions about the task before us — slowing, halting and reversing global warming — may be too focused on high-tech carbon removal technologies. Planting trees and maintaining healthy forests might deserve a higher place on the priority list for carbon removal, the study suggests."

The linkage of the post-Columbus human disaster and climate cooling remains controversial, though it's accepted by an increasing number of mainstream experts, and the paper has gotten some pushback.

  • "The paper is thought-provoking, but it gives a certainty about this relationship that is not justified," says Dagomar Degroot, a professor at Georgetown, who says he has taught the theory for three or four years.
  • "I don't want to say the article is wrong or not interesting. ... [But] you can't isolate things to America without a clear sense of what was happening globally. We don't have that yet. A lot of scholarship is still in flux," Degroot tells Axios.

The research follows up on pioneering research by William Ruddiman, an emeritus professor at the University of Virginia. Since the early 2000s, Ruddiman has argued that humans began to alter the climate as soon as they organized farming 5,000 to 8,000 years ago.

  • Andrew Koch, lead co-author of the paper, tells Axios the research was meant to pull together and rationalize all of the research by Ruddiman and others, including the carbon record from ice cores pulled from Antarctica. "No one had really reviewed all of it," Koch said.
  • Ruddiman, reached at home in Virginia, said he was a peer reviewer of the paper and that he had only one quibble, which the authors handled in a footnote. It was on the amount of acreage taken up by farms and burning, which Ruddiman said was actually much larger.

The results vastly increase popular notions of how many people inhabited the New World at the time Europeans arrived: There were about 60 million people, requiring the cultivation of a little over 1 hectare of land each, or a total of about 60 million hectares.

  • "The cessation of farming doubled the cooling of the Little Ice Age," said Mark Maslin, a professor at University College London and a co-author both of the paper and a new book, "Human Planet: How We Created the Anthropocene."
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