Did Humans Cause the Ice Age?

A. Tsiongas

On February 2, 2007 the Intergovernmental Panel on Climate Change, a U.N.-sponsored collective of hundreds of scientists from around the world, released a report stating that rising temperatures on the Earth’s surface and a rise in sea level could, with over 90% certainty, be attributed to humans. These negative climatic effects which could “continue for centuries” – despite any attempts by humans to control their pollution – are mainly the result of the use of fossil fuels (oil, gas, and coal) by humans, and of human agriculture. These activities have upped concentrations of heating-trapping greenhouse gases in the Earth’s atmosphere, and drastically warmed our climate.

In fact, since at least 50,000 years ago humans have had the ability to drastically (if not permanently) alter the Earth’s climate with their hunting and agricultural practices. Early humans may not have churned out processed, packaged food from factories, gobbling up millions of tons of the Earth’s precious fossil fuels in the process, but it’s safe to say they did employ large-scale burning of vegetation to hunt and to encourage certain types of favored plant growth. These raging fires are now viewed as the cause of Australia’s transition (about 50,000 years ago, roughly the time when humans first arrived on the continent) from a tropical to a desert climate. Australia, geologist Gifford Miller states bluntly, never has and likely never will recover from this dramatic “increase in aridity.”

Is it not, then, reasonable to suggest that perhaps throughout their history humans have been igniting widespread climate change? They have been attributed with global warming – are they equally as capable of global cooling? Did early humans… cause the Ice Age?

If early human ancestors (namely, of the genus Homo) were using the same kind of destructive hunting techniques seen in Australia as early as 2.5 million years ago, then the fires responsible for drying the African savannas could have been artificially induced ones. The spread of grasslands into once tropical regions might have caused a cooler, drier climate and provided (in addition to other factors) the climatic imbalance necessary for the start of an Ice Age. Great amounts of carbon dioxide and carbon monoxide are released in the air as a result of biomass burning, which is what Homo would have caused with their artificial fires, not to mention tropospheric ozone, a poisonous greenhouse gas, which may have swept over the continent of Africa as well as the surrounding oceans. Further cooling of the Earth may also be attributed to the increased activity of the oceans’ natural CO 2 pump: as more CO 2 was released into the atmosphere, more CO 2 is absorbed by algae blooms, or stored in the ocean depths to be remineralized and to surge back up 500-2,000 years later. Land erosion would only increase algal growth, which brings with it the release of dimethyl sulfide gas, believed to be oxidized into a dangerous aerosol by the Earth’s atmosphere.

However, there are several major fallacies in the assertion that early human ignited this large-scale global cooling. First of all, the earliest accepted evidence of domesticated fire is from about 1.4 million years ago, creating a large discrepancy between this date and the time humans would have had to have set Africa aflame to start an ice age; namely, about 1 million years earlier. Homo itself is only thought to have been in existence since about 2.4 million years ago, when the shift to a drier climate was already taking effect 2.5 million years ago. If artificial fires were indeed occurring before 2.5 million years ago, who on Earth could have started them? In fact, the widely accepted scientific opinion is that fires occurring this early in the Africa savanna were natural fires, of which there exists abundance evidence dating back 350 million years. The ice ages in our history were most likely produced in part by plate tectonics and by increased carbon dioxide in our atmosphere as a result of metamorphic degassing, the weathering of organic carbon, the weathering of silicates, and the burial of organic carbon, but NOT artificial fires created by early humans.

However, humans’ destructive power, as demonstrated in Australia some 50,000 years ago, as well as today, is no myth. The introduction of human communities to the continent of Australia wiped out – and rapidly – an entire ecosystem which supported an abundance of mega fauna, 85% of which perished as result. Scientists have reason to believe something similar occurred in the Americas.

Human technologies continue to prove their great influence on our Earth’s climate, something which today, the Intergovernmental Panel on Climate Change has provided definitive evidence of. However, to assert that humans were the driving force behind a major ice age is incredibly dubious, if not entirely baseless.


World Archaeology and Global Change: Did Our Ancestors Ignite the Ice Age?
Peter Westbroek; Matthew J. Collins; J. H. Fred Jansen; Lee M. Talbot
World Archaeology, Vol. 25, No. 1, Biomolecular Archaeology. (Jun., 1993), pp. 122-133.

Maasch, Kirk A. “The Big Chill.” Cracking the Ice Age, NOVA online.

"U.N. Report: Humans Behind Climate Change." All Things Considered. NPR, 02 Feb. 2007

“Megafauna Extinction.” Morning Edition. NPR, 08 Jan. 1999

“Aboriginal Climate Change.” Weekend Edition Sunday. NPR, 17 Mar. 2002



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