We'd Be Entering an Ice Age Right Now if Climate Change Hadn't Terminated It, Study Suggests

Earth is constantly molded by fire and ice, and not in a poetic sense.

These physical forces singe or scour our planet's surface with fiery eruptions or the unstoppable march of glaciers.

On the chilly side, Earth has experienced at least five ice ages, including some potential snowball or slushball episodes, if we delve into deep time.

We're in a geological ice age right now, in fact, but we're currently in a balmier interglacial period, which began approximately 11,700 years ago, around the time many fluffy megafauna started going extinct.

These warmer periods fluctuate with colder, icier periods that host great glaciers – what we colloquially call 'ice ages' and associate with woolly mammoths and shivering cave-dwellers huddling over meager fires.

Actually, the next of these ice ages may have already begun about 2,000 years ago, only to be cut short by human-driven climate change, a new study published in the journal Science suggests.

"It was just getting started, everything was normal, the next glaciation was about to happen – and yet it stopped," says Nicolás Young, a geochemist at Columbia University and the study's first author.

The study focused on the Laurentide Ice Sheet (LIS), the largest such structure of the Pleistocene, which covered a great deal of the northern US and Canada from around 95,000 to 20,000 years ago.

At its maximum, it stretched its frigid grip from the Arctic Circle to Illinois, covering these ancient lands in up to 3 kilometers (2 miles) of ice.

Its overall ice volume may have been equivalent to around 80 meters (260 feet) of sea-level shift.

The LIS devolved into the majestic Barnes Ice Cap (BIC), the little but still-beating heart of an entire ice age, researchers suggest.

To reach that conclusion, the researchers created an ice cap chronology using two primary lines of in-situ evidence, based on atomic dating methods.

They homed in on different types of rock to gauge the ratio of cosmogenic beryllium-10, an isotope (atomic variant) of the element beryllium. It's produced as cosmic radiation from huge exploding stars smashes into our planet.

They also analyzed the long-dead vegetation revealed as the BIC retreated, to measure the ratio of carbon-14, a benignly radioactive carbon with a predictable decay rate.

Both these measures act like terrestrial stopwatches. In rocks, beryllium-10 accumulation stops when advancing glaciation shields stones from the Universe's invisible bombardment. Accumulation then resumes when the rocks are uncovered as the ice retreats.

In the plants, the carbon stopwatch starts when they're encased beneath advancing ice, because dead vegetation no longer inhales carbon.

Altogether, the researchers put together a concise chain of climate change.

The highest temperatures of our current interglacial period, called the Holocene, may have occurred around 11,000 to 10,000 years ago – at least in northerly climes – driven by high solar irradiation due to Earth's shifting orbit, known as "Milankovitch cycles".

The following millennia welcomed a cooling trend, but, surprisingly, the LIS kept shrinking because its surface had sunk too low for it to keep growing, leaving it out of step with the climate.

By 3,600 years ago, it had shrunk to smaller than it is today, and it stayed at that minimum until around 2,000 years ago.

It wasn't until around 2,000 years ago that it started expanding, representing the inception of the next glaciation.

Or rather, the starting point for a would-be ice age, if not for the influence of warming summer temperatures beginning in the 1960s, the researchers suggest.

They report that the BIC reached its historical maximum around 1960. Then, with its frozen mind presumably set on world domination, anthropogenic warming reversed its growth, tipping it into a negative mass balance, melting faster in warm months than it could recover in the winter.

Since then, its losses "can be almost entirely explained by rising summer temperatures" which are shrinking other ice caps across the Canadian Arctic and the North Atlantic, the researchers say, in a culmination of increasing greenhouse gas emissions dating back to around 1750.

Around this time, the Industrial Revolution began to significantly pollute our atmosphere with greenhouse gases.

This came just as the climate was experiencing the coldest century of the most teeth-chattering, lip-chapping period in recent history, the Little Ice Age, with its chilliest episode lasting from 1780 to 1880.

But what about the future? Models suggest the former LIS, or the current BIC, or some future mix of these two terms, will be gone for good under current climate profiles, a vestige of an old world lost forever.

"That will be the true very last remains of the Laurentide, disappearing for good," Young concludes.

"What has been an extremely natural and predictable phenomenon is now gone."

The research has been published in Science.