While visiting Barcelona during our recent trip, we rested for a moment on stone steps that led to a palace where Christopher Columbus was greeted by King Ferdinand and Queen Isabella upon his return from his historic voyage to the New World. It reminded me of an article I had read a year or so earlier about how Columbus was responsible for, of all things, an interval of global cooling. Seriously!

When we returned to the U.S., I looked the article up. As I suspected, the main actor was our old friend carbon.

Contrary to popular belief, as author Charles Mann eloquently explains in his book 1491, the New World was not a wilderness. Instead, it was a landscape full of people, perhaps as many as 100 million, all of them busy hunting, planting, raiding, building, laughing, singing. And all these millions of busy people had a profound impact on the land, including the clearing of large swaths of forests for intensive slash-and-burn agriculture, expanding cities and villages, and the production of charcoal to improve nutritionally ‘thin’ soils, especially in the Amazon Basin. Estimates of how much forested land might have been cleared of trees at the time of Columbus’ fateful arrival are hard to determine, but researchers are certain that it was high.

Enter the Europeans – and their diseases, including smallpox and diphtheria. As Mann painfully recounts, more than 90% of the pre-contact indigenous population of the Americas died in the wake of the European conquest – died of disease, not warfare. This sudden change had a profound impact on the environment.

“Until Columbus,” wrote Mann, “Indians were a keystone species in most of the hemisphere. Annually burning undergrowth, clearing and replanting forests, building canals and raising fields, hunting bison and netting salmon, growing maize and manioc, Native Americans had been managing their environment for thousands of years…But all of these efforts required close, continual oversight. In the sixteenth century, epidemics removed the boss.”

Here’s a photo from a modern slash-and-burn plot:

With the boss gone, the trees grew back. This is where carbon comes in. According to Stanford University geochemist Richard Nevle in an article published online last year in ScienceNews, the restoration of the forests after the massive die off of Native Americans pulled billions of tons of carbon dioxide from the atmosphere, which in turn diminished the heat-trapping capacity of the atmosphere and cooled the climate for a while. In previously published research, Nevle and his colleagues reported that ice cores from Antarctica showed a drop in carbon dioxide levels by 6 to 10 parts per million between 1525 and the early 1600s. Now Nevle thought he knew why.

“We have a massive reforestation event that’s sequestering carbon …coincident with the European arrival,” said Nevle in the article.

Tying together many different lines of evidence, Nevle estimated that this new growth could have soaked up between 2 billion and 17 billion metric tons of carbon dioxide from the air. According to Nevle, that was potentially enough to augment Europe’s so-called Little Ice Age – centuries of cooler temperatures that followed the Middle Ages. One line of evidence from the ice cores is the increasing presence of carbon-13 over these decades. Trees prefer carbon-12 (one neutron lighter), leaving the heavier version of carbon dioxide in the atmosphere.

“There’s nothing else happening in the rest of the world at this time, in terms of human land use, that could explain this rapid carbon uptake,” said Jed Kaplan, an earth systems scientist at the Federal Polytechnic School of Lausanne in Switzerland.

Kaplan pointed out that while the evidence isn’t conclusive, it does demonstrate that the New World epidemics highlight mankind’s ability to influence the climate long before the start Industrial Revolution.

It also demonstrates the critical role that trees and other vegetation play in the planet’s carbon cycle, as well as why so many people are working today on climate change mitigation and adaptation strategies that focus on forests. Protecting forests from destruction, especially in the tropics, is usually near the top of all the ‘To Do’ lists of scientists and conservationists. Professor Nevle’s research added a punctuation point to their arguments!

Rereading the article, and the extensive online comments it generated, I was reminded of just how raw the wound opened by Columbus remains in this country. Hero or Villain? When I was a kid, Christopher Columbus was portrayed as indisputably heroic. There was even a federal holiday named after him (no school!). However, by the time of the 500th anniversary of his famous voyage into “the ocean blue,” Columbus’ reputation was in tatters, especially as Native Americans began to speak up, encapsulated in an emotional 1992 documentary called Surviving Columbus. Throw climate change into the mix, as Dr. Nevle did, and you have a volatile recipe for lots of strong feelings still. Did Columbus “cause” the Little Ice Age? Yes! No! Yes! No!

Lost in the raw emotions is a simple fact: we continue to underestimate the impact of human activity on the natural world. We did it when contemplating the world in 1491, and we’re doing it today. Fortunately, with science’s help, we’re getting a clearer picture of our impact, then and now. Hopefully, it’ll help us clear our heads as well.

Here we are thinking about colonial adventures: