Many Americans doubt man-made global warming because they don’t think humans could so fundamentally change the world. Some believe only God could alter the climate. But small groups of Homo sapiens have been re-engineering the environment on a massive scale for thousands of years, using only primitive tools. Many scientist think that includes ancient man-made global warming.
Most of us know that humans have been cutting down forests and wiping out animal species for millennia. But we rarely recognize the scale of past people’s impact — and not just of metal-wielding farmers, like the peasants who transformed Europe’s vast forests into meadows and farms. When Old World explorers reached North America, for instance, they found a land of open woodlands, great prairies, and vast buffalo herds. Some researchers think that environment was largely man-made. The Native Americans had long before thinned the woods and, wielding fire, cleared and expanded the prairies. They were opening up farmland and easy foraging grounds, according to the theory, as well as grazing country for the buffalo and elk they hunted. And they did it without modern technology or even significant metal tools.
Another theory says Stone Age hunter-gatherers reshaped Australia on an even larger scale, again with fire. When the Aborigines arrived around 45,000 years ago, much of Australia was dense forest. But the forests soon disappeared, replaced by deserts and plains, as well as limited open woodlands. Scientists think the Aborigines burnt away the trees and undergrowth to clear friendlier pastures for themselves and their preferred prey, particularly kangaroos and wallabies. They created and managed the “natural” Outback: a continental park four times the size of Britain, Germany, France, and Spain combined. Researchers think the Aborigines’ fire-clearing even reduced Australia’s rainfall, by altering evaporation and reflection from the land’s surface. And they did it with Stone Age tools.
Even the Outback is just the tip of the iceberg. Another theory holds that ancient people altered the entire world’s climate. Ice ages have gripped the Earth for more than 2.5 million years, occasionally interrupted by short warming periods, called “interglacials.” We live in an interglacial that began almost 12,000 years ago (the Holocene). Some scientists think the current interglacial would have ended millennia ago, plunging humanity back into ice age, if not for farming during the past 8,000 or more years. By clearing land and cultivating it, human beings released greenhouse gases (CO2 and methane). That stalled the natural cooling process and delayed the ice’s return.
Eight thousand years ago, the Earth was home to something like 10 million people. Today, there are more than 7 billion human beings. Some of the theories above are controversial, but if it’s even possible for a few million people to re-engineer the environment and warm the planet with primitive tools, what might billions do with industrial power?
- Bison illustration: Bull Buffalo, lithograph of painting by George Catlin (c. 1846).
- Re-engineering North America: see, 1491, New Revelations of the Americas Before Columbus, by Charles Mann.
- Outback photo: Australian Outback: Mount Conner/Attila, a mesa between near Uluru, by Gabriele Delhey (2003), provided through Wikimedia Commons.
- Re-engineering Australia: see, The Biggest Estate on Earth, How Aborigines Made Australia, by Bill Gammage.
- Australian climate change: Karl-Heinz Wyrwoll (2012) — “How Aboriginal burning changed Australia’s climate,” published online at The Conversation.
- Ice age drawing: Fauna de la Edad del Hielo, Mauricio Antón, 2008 — cropped, provided through Wikimedia Commons.
- Interglacial theory: Ruddiman (2003) — “The Anthropogenic Greenhouse Era Began Thousands of Years Ago,” Climatic Change 61: 261–293.
- Historical population figures: U.S. Census Bureau historical population estimates; Max Roser (2015) — “World Population Growth,” published online at OurWorldInData.org.
© 2016 by David W. Tollen. All rights reserved.