Earth’s ice age cycles are predictable - but humans may change that

Earth has never been a stranger to changes in the ice age cycle. Around 2.5 million years ago, the planet settled into a rhythm – glaciers advanced, then melted back, over and over again. The last big freeze ended about 11,700 years ago, leaving us in a warm, stable period. But how long will this last?

If history followed its usual script, the next ice age would arrive in roughly 10,000 years, according to a new study. A team of researchers, including scientists from UC Santa Barbara, has traced the subtle shifts in Earth’s orbit. These wobbles and tilts are so slight that they seem insignificant.

Yet, over thousands of years, these changes have consistently transformed the planet’s climate. The findings reveal a strikingly predictable pattern in Earth’s natural cycles.

Subtle mechanics of a changing climate

The team combed through a million years of climate records, tracking how ice sheets across the Northern Hemisphere expanded and shrank.

The researchers compared those shifts to the temperature of deep ocean waters, which represent cold storage in terms of Earth’s climate history. Then, they lined it all up with data about variations in Earth’s orbit.

It turns out, every major climate shift follows a script dictated by these orbital quirks.

“We found a predictable pattern over the past million years for the timing of when Earth’s climate changes between glacial ‘ice ages’ and mild warm periods like today, called interglacials,” said Lorraine Lisiecki, a professor in UCSB’s Earth Science Department.

Some orbital changes signaled the end of an ice age, while others set the stage for a new one.

A pattern hidden in plain sight

Scientists have long suspected that Earth’s orbit plays a role in glacial cycles. The idea dates back over a century. But proving it? That took time.

Not until the mid-1970s did data begin to confirm the connection. Even then, the details remained murky. Now, thanks to this new study, those details are much clearer.

“We were amazed to find such a clear imprint of the different orbital parameters on the climate record. It is quite hard to believe that the pattern has not been seen before,” expressed Stephen Barker, a professor at Cardiff University.

Earth’s next ice age – on hold?

Looking at the past 900,000 years, the team uncovered a pattern. Left to its own devices, Earth would remain in this warm interglacial period for several more millennia before the next deep freeze began.

“The pattern we found is so reproducible that we were able to make an accurate prediction of when each interglacial period of the past million years or so would occur and how long each would last,” Barker said.

This discovery confirms that climate changes over tens of thousands of years are anything but random. But there’s a catch. The planet’s natural rhythm assumes nothing interferes.

Humans have changed the natural cycle

“And because we are now living in an interglacial period – called the Holocene – we are also able to provide an initial prediction of when our climate might return to a glacial state,” noted Chronis Tzedakis, a professor at University College London.

The problem? Human activity has already thrown the system off course.

“But such a transition to a glacial state in 10,000 years’ time is very unlikely to happen because human emissions of carbon dioxide into the atmosphere have already diverted the climate from its natural course, with longer-term impacts into the future,” added Gregor Knorr from the Alfred Wegener Institute.

Looking at Earth’s future climate

The research team isn’t stopping here. They plan to refine their predictions, calibrating past climate changes to create a clearer picture of what Earth’s climate should look like over the next 10,000 to 20,000 years.

Combined with modern climate models, this data could reveal the full extent of human influence on the planet.

“Now we know that climate is largely predictable over these long timescales, we can actually use past changes to inform us about what could happen in the future,” Barker said. “This is something we couldn’t do before with the level of confidence that our new analysis provides.”

Understanding these cycles matters. It’s not just about predicting the next ice age – it’s about understanding how our choices today reshape the climate for millennia to come.

The study is published in the journal Science.

Image Credit: Matt Perko, UC Santa Barbara

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