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A new study suggests that human activity may have staved off an ice age in the 1800s, and is likely to delay the next one for tens of thousands of years.

Researchers from the Potsdam Institute for Climate Impact Research in Germany and the Santa Fe Institute in New Mexico presented their analysis in Nature this week.

The team set out to explain the conditions that lead to the eight ice ages in Earth's history, and found that human activity has interrupted the natural cycle. The scientists' modeling showed that insolation—or exposure to rays from the sun—and carbon dioxide levels interact to bring on an ice age. The extra carbon dioxide emissions that happened at the start of the Industrial Revolution may have, according to the researchers, prevented an ice age in the mid-1800s. They explain in their abstract:

Here we propose a critical functional relationship between boreal summer insolation and global carbon dioxide (CO2) concentration, which explains the beginning of the past eight glacial cycles and might anticipate future periods of glacial inception. Using an ensemble of simulations generated by an Earth system model… we suggest that glacial inception was narrowly missed before the beginning of the Industrial Revolution. The missed inception can be accounted for by the combined effect of relatively high late-Holocene CO2 concentrations and the low orbital eccentricity of the Earth.

The scientists don't explicitly link the high CO2 levels of that period to human activity, but the question has been raised by others. One climate scientist, William Ruddiman, told the Washington Post that he sees a clear link between pre-Industrial Revolution human activity and the delayed ice age. The Post notes that, "Ruddiman agreed with the [researchers'] work overall but questioned why the authors didn’t more fully embrace… the idea that pre-industrial humans headed off a coming ice age through their alterations of the planet’s land surface, even without mass burning of fossil fuels."


In his view, humans have interrupted Earth's natural cycles for ages. "While there is little doubt that industrial-era anthropogenic emissions are now forestalling any possibility of a new ice age, the evidence shown here suggests that this major human intervention started millennia ago," he said.

So it seems the technological innovations that brought us modern agriculture could also have saved humanity from a 100,000-year ice age. Phew.

The scientists predict that without greenhouse gas emissions, we'd likely be about 50,000 years away from another ice age. But thanks to global warming, we're probably closer to 100,000 years away. Lead author Andrey Ganopolski said in a statement, "Our study also shows that relatively moderate additional anthropogenic CO2-emissions from burning oil, coal and gas are already sufficient to postpone the next ice age for another 50.000 years."


Ganopolski added that "The bottom line is that we are basically skipping a whole glacial cycle, which is unprecedented. It is mind-boggling that humankind is able to interfere with a mechanism that shaped the world as we know it.”

The researchers add that the are, ironically, long-term benefits to an ice age. Co-author Hans Joachim Schellnhuber explained that, "Like no other force on the planet, ice ages have shaped the global environment and thereby determined the development of human civilization. For instance, we owe our fertile soil to the last ice age that also carved out today’s landscapes, leaving glaciers and rivers behind, forming fjords, moraines and lakes."

Don't worry though, we've got a new geological force to replace ice ages now. Said Schellnhuber, "today it is humankind with its emissions from burning fossil fuels that determines the future development of the planet." How encouraging.


Danielle Wiener-Bronner is a news reporter.