European contact with the Americas may have triggered global cooling


INTRO: When Europeans arrived in the Americas in 1492, they found two continents populated by as many as 60 million people: 10% of the world’s population. Within 100 years, 90% of indigenous Americans were dead from genocide and disease. A new study in Quaternary Science Reviews links this abrupt loss in life to a dip in atmospheric carbon dioxide that may have contributed to the coldest snaps of the Little Ice Age.

The Little Ice Age describes a period of global cooling between roughly the 13th and 19th centuries that saw frozen rivers across Europe, crop failure and famine in Asia, and glacial expansion in both the Northern and Southern Hemispheres. This widespread cooling trend was likely triggered by a combination of increased volcanism, changes in ocean circulation patterns, and variations in Earth’s orbit.
Embedded within the Little Ice Age are three notably colder intervals starting in 1610, 1770, and 1850, each separated by periods of slight warming. The new study proposes that the first of these dips may be rooted in the drastic population declines wrought by the European arrival in the Americas.

“Most of the Little Ice Age [was] caused by volcanic eruptions, fluctuations in solar output, and associated feedback processes,” says Alexander Koch, a geographer at University College London and lead author of the new study. “But the early 1600s, when temperatures were the coldest, coincides with the lowest carbon dioxide concentrations.”

Koch and his colleagues attribute this dip in atmospheric carbon dioxide—a greenhouse gas associated with warming—to the loss of more than 50 million people in the Americas in the preceding century. The hypothesis is not a new one, Koch says. [...] “With drastically fewer people in the Americas, there was a lot less agriculture and a lot less burning,” Koch says... (MORE - details)

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