How global warming today could trigger a future ice age

Earth has never stood still when it comes to climate. For billions of years, our planet has cycled between heat and cold, shaping the environment where life evolved.

But new research from UC Riverside (UCR) reveals that the story of Earth’s carbon balance is more complicated than once believed.

The findings suggest that global warming could eventually tip into the opposite extreme – another ice age.

Rocks regulate Earth’s climate

The common scientific view has been that Earth regulates temperature through rock weathering. When rainwater absorbs carbon dioxide, it interacts with rocks on land, especially silicate-rich ones like granite.

This chemical process dissolves minerals, and the captured carbon eventually travels to the ocean. There, it combines with calcium, forming shells and limestone reefs that lock away carbon for hundreds of millions of years.

“As the planet gets hotter, rocks weather faster and take up more CO₂, cooling the planet back down again,” said Andy Ridgwell, a UCR geologist and co-author of the study.

This system works slowly but reliably, helping to stabilize climate over geological timescales. Yet history shows it is not always enough.

Past warming sparked ice ages

Evidence from Earth’s deep past reveals episodes when the entire planet froze, turning into a snowball world. Such drastic shifts suggest that rock weathering alone cannot explain the extremes.

Something else was at work, driving stronger feedbacks that plunged Earth into global ice. Researchers point to carbon burial in the oceans as the missing link.

As carbon dioxide levels rise and the planet warms, more nutrients like phosphorus wash into the seas. These nutrients fuel plankton growth. Plankton absorb carbon while alive and, after death, carry it to the ocean floor.

Earth’s oceans link heat to ice

At first, this seems like a powerful stabilizing process. But as warmer oceans lose oxygen, phosphorus gets recycled instead of buried.

This creates a loop: more nutrients feed more plankton, their decay removes oxygen, and the cycle repeats. With every turn of the loop, larger amounts of carbon get buried, rapidly cooling Earth.

Rather than keeping climate steady, this system overshoots, pushing temperatures far below their starting point. Computer models in the new study show that such runaway cooling could trigger ice ages.

Thermostat gone wild

Ridgwell likens the process to a household thermostat. “In summer, you set your thermostat around 78°F. As the air temperature climbs outside during the day, the air conditioning removes the excess heat inside until the room temperature comes down to 78 and then it stops,” he said.

But Earth’s thermostat does not always respond evenly. “It might not be in the same room as the air conditioning unit, making performance uneven,” he added.

In earlier eras with lower atmospheric oxygen, this imbalance made the climate far more erratic, producing extreme glaciations.

Human carbon speeds the shift

With modern human activity adding vast amounts of CO₂, a hotter planet will continue in the near future.

The model predicts another cooling overshoot caused by warming could follow, though it would be less severe than ancient ice ages. Higher oxygen levels today dampen the nutrient feedback, softening the effect.

“Like placing the thermostat closer to the AC unit,” Ridgwell said. Even so, this could still accelerate the arrival of the next ice age.

“At the end of the day, does it matter much if the start of the next ice age is 50, 100, or 200 thousand years into the future?”

“We need to focus now on limiting ongoing warming. That the Earth will eventually cool back down, in however wobbly a way, is not going to happen fast enough to help us out in this lifetime.”

Lessons from Earth’s past

What makes this study powerful is the reminder that Earth’s systems are not always gentle. Geological history shows that balance often comes through dramatic swings.

Snowball Earth episodes hundreds of millions of years ago nearly wiped out early life forms. Yet they also set the stage for evolutionary leaps once the planet thawed.

Scientists studying these patterns use them as warnings and guides. They reveal how climate can shift suddenly and how feedback loops can make the difference between stability and catastrophe.

The human perspective

Today, humanity has entered this cycle as a driver of change. By burning fossil fuels, we are accelerating carbon buildup at a pace unmatched in Earth’s past.

While the natural thermostat may eventually cool the planet, that correction could take hundreds of thousands of years.

For humans, waiting that long is not an option. The focus must remain on managing current warming.

The UC Riverside study highlights how Earth’s deep memory is written in ice, rocks, and oceans. It shows us that climate balance is not guaranteed and that small actions can tip the system into extremes.

Models sharpen climate predictions

Understanding these feedbacks also sharpens predictions for Earth’s future. Researchers continue refining models to capture both the slow grind of rock weathering and the fast bursts of nutrient-driven cooling.

These efforts help answer critical questions: How close are we to thresholds? How might human activity influence the timing of natural cycles?

For now, one message stands clear. While Earth may one day swing back into deep cold, that turn is far away. The immediate challenge is the heat building now. What we choose to do today will decide how livable our world remains in the centuries ahead.

The study is published in the journal Science.

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