The great dying
In 1492, Christopher Columbus reached the Americas. Over the following decades, Europeans began colonising them. In the process, they fought with Indigenous Americans, often killing them. But even more lethally, they brought diseases. One of the worst was smallpox, which killed millions.
As well as being a genocide and a tragedy, this may have had an impact on the climate. Many Indigenous Americans were farmers who had cleared forests for their crops and when they died the trees grew back, drawing carbon dioxide out of the air and cooling the planet. This scenario was first outlined by climatologist William Ruddiman in 2003, as part of his “early Anthropocene” hypothesis that humans have been affecting Earth’s climate for millennia, albeit less than we are today.
The arrival of Europeans in the Americas caused the deaths of millions of Native people. The forests that grew on formerly cultivated land took carbon from the atmosphere. Photograph: John Mitchell/Alamy
The idea that mass deaths among Indigenous Americans led to climate cooling has received tentative support from modelling studies. Still, it has been controversial because there are so many uncertainties about the key numbers.
However, in 2019 Koch and his colleagues published an updated analysis. They went through the argument step by step and tried to quantify everything, from the number of people who died to the extent of reforestation. They concluded that the European arrival led to 56m deaths by 1600. This dreadful toll meant trees grew again on 56m hectares of land, removing 27.4bn bn kilograms of carbon dioxide from the air.
“It’s a really interesting theory,” says Degroot. However, he remains sceptical because we don’t know how land use was changing in other parts of the world, especially Africa.
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