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The Colonization of the Americas Cooled the Earth

A new paper from researchers at University College London argues that the genocide of indigenous peoples in the Americans after Columbus’s landing in 1492 had a significant effect on the Earth’s global climate and was a major cause of the Little Ice Age, the dip in global temperatures from the 16th to the 19th centuries. They estimate that 55 million indigenous people died during Europe’s conquest of the Americas (~90% of the population), and the 56 million hectares of land that they had cleared of vegetation (roughly the area of Kenya) was then reclaimed by forests, which then took in more carbon dioxide, reduced the greenhouse effect, and caused the Earth to cool. From the paper’s conclusion:

We calculate that this led to an additional 7.4 Pg C being removed from the atmosphere and stored on the land surface in the 1500s. This was a change from the 1400s of 9.9 Pg C (5 ppm CO2). Including feedback processes this contributed between 47% and 67% of the 15-22 Pg C (7-10 ppm CO2) decline in atmospheric CO2 between 1520 CE and 1610 CE seen in Antarctic ice core records. These changes show that the Great Dying of the Indigenous Peoples of the Americas is necessary for a parsimonious explanation of the anomalous decrease in atmospheric CO2 at that time and the resulting decline in global surface air temperatures.

Little Ice Age Graph

The authors also assert that this effect of human action on global climate marks the beginning of the Anthropocene epoch.

I first heard about this theory from Charles Mann’s excellent 1493, which led me to William Ruddiman’s 2003 paper. I heard about this most recent study from Mann too… he called it “most careful study of the impacts of Euro conquest of Americas I’ve yet seen”.

If you’re not up for reading the paper itself, you can check out the coverage from the BBC, the Guardian, Nature, or the NY Times.

How the Potato Changed the World

In recent years, authors have claimed that many seemingly boring things have changed the world but a particularly strong case can be made for the potato and Charles C. Mann makes it.

The effects of this transformation were so striking that any general history of Europe without an entry in its index for S. tuberosum should be ignored. Hunger was a familiar presence in 17th- and 18th-century Europe. Cities were provisioned reasonably well in most years, their granaries carefully monitored, but country people teetered on a precipice. France, the historian Fernand Braudel once calculated, had 40 nationwide famines between 1500 and 1800, more than one per decade. This appalling figure is an underestimate, he wrote, “because it omits the hundreds and hundreds of local famines.” France was not exceptional; England had 17 national and big regional famines between 1523 and 1623. The continent simply could not reliably feed itself.

The potato changed all that. Every year, many farmers left fallow as much as half of their grain land, to rest the soil and fight weeds (which were plowed under in summer). Now smallholders could grow potatoes on the fallow land, controlling weeds by hoeing. Because potatoes were so productive, the effective result, in terms of calories, was to double Europe’s food supply.

Mann talks more about the potato in his excellent 1493: Uncovering the New World Columbus Created.

Did Columbus cause The Little Ice Age?

I’m slowly working my way through Charles Mann’s 1493 and there are interesting tidbits on almost every page. One of my favorite bits of the book so far is a possible explanation of the Little Ice Age that I hadn’t heard before put forth by William Ruddiman.

As human communities grow, Ruddiman pointed out, they open more land for farms and cut down more trees for fuel and shelter. In Europe and Asia, forests were cut down with the ax. In the Americas before [Columbus], the primary tool was fire. For weeks on end, smoke from Indian bonfires shrouded Florida, California, and the Great Plains.

Burning like this happened all over the pre-Columbian Americas, from present-day New England to Mexico to the Amazon basin to Argentina. Then the Europeans came:

Enter now the Columbian Exchange. Eurasian bacteria, viruses, and parasites sweep through the Americas, killing huge numbers of people โ€” and unraveling the millenia-old network of human intervention. Flames subside to embers across the Western Hemisphere as Indian torches are stilled. In the forests, fire-hating trees like oak and hickory muscle aside fire-loving species like loblolly, longleaf, and slash pine, which are so dependent on regular burning that their cones will only open and release seed when exposed to flame. Animals that Indians had hunted, keeping their numbers down, suddenly flourish in great numbers. And so on.

The regular fires and forest regrowth resulted in less carbon dioxide in the atmosphere and the atmosphere traps less heat. It’s like global warming in reverse.

In 1493, Columbus reunited the biological family tree

Tyler Cowen says that Charles Mann’s 1491 (a taste of which can be read here) is “one of my favorite books ever, in any field”, to which I add a hearty “me too”. Mann’s been hard at work at a sequel, 1493: Uncovering the New World Columbus Created, which is due out in August, just in time for some seriously awesome beach reading.

From the author of 1491 โ€” the best-selling study of the pre-Columbian Americas โ€” a deeply engaging new history that explores the most momentous biological event since the death of the dinosaurs.

More than 200 million years ago, geological forces split apart the continents. Isolated from each other, the two halves of the world developed totally different suites of plants and animals. Columbus’s voyages brought them back together โ€” and marked the beginning of an extraordinary exchange of flora and fauna between Eurasia and the Americas. As Charles Mann shows, this global ecological tumult โ€” the “Columbian Exchange” โ€” underlies much of subsequent human history. Presenting the latest generation of research by scientists, Mann shows how the creation of this worldwide network of exchange fostered the rise of Europe, devastated imperial China, convulsed Africa, and for two centuries made Manila and Mexico City โ€” where Asia, Europe, and the new frontier of the Americas dynamically interacted โ€” the center of the world.