Earth Could Overcorrect Global Warming, Triggering an Ice Age

[Renaud de RICHTER]

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Earth Could Overcorrect Global Warming, Triggering an Ice Age

07/10/2025

Reference: “Instability in the geological regulation of Earth’s climate” by Dominik Hülse and Andy Ridgwell, 25 September 2025, Science.
DOI: 10.1126/science.adh7730

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New research suggests that Earth’s ancient ice ages may have been triggered not just by rock weathering, but by a powerful ocean feedback loop, one that could, in time, cool the planet again. Credit: Shutterstock

New research reveals how the Earth might overcorrect for global warming.

For a long time, scientists believed that the gradual breakdown of silicate rocks played the leading role in regulating Earth’s climate. In this natural process, rain absorbs carbon dioxide (CO2) from the atmosphere and falls onto exposed rock surfaces, where it slowly dissolves the minerals. The resulting chemical reactions carry carbon and calcium into the oceans, where they serve as building blocks for shells and coral reefs. Over millions of years, these materials accumulate on the seafloor, locking away carbon deep within the Earth.

“When the planet warms, rocks weather faster and absorb more CO₂, allowing the Earth to cool down again,” explains Dominik Hülse.

However, throughout Earth’s history, there have been times when the entire planet was shrouded in snow and ice. The researchers note that these extreme glaciations cannot be explained by rock weathering alone, meaning other mechanisms must have contributed to the planet’s deep freeze.

One key factor appears to be how carbon is stored in the ocean floor. As atmospheric CO2 levels rise and the planet warms, more nutrients, particularly phosphorus, are carried into the oceans. These nutrients fuel the growth of algae that capture carbon through photosynthesis. When the algae die, they sink to the seabed, carrying the trapped carbon with them.

Feedback Loops and Oxygen Loss

In a warmer world with enhanced algae growth, however, the oceans also lose oxygen, which results in the recycling of phosphorus rather than it being stored long-term in the sediments. This creates a feedback loop: the availability of more nutrients in the water results in more algae, whose decomposition in turn consumes more oxygen, causing even more nutrients to be recycled. At the same time, large amounts of carbon are buried in the sediments, which causes the Earth to cool.

For several years, Hülse and Ridgwell have been refining a computer model of the Earth System by incorporating more of these processes. “This more complete Earth System model does not always stabilize the climate gradually after a warming phase, rather it can overcompensate and cool the Earth far below its initial temperature — a process that can still take hundreds of thousands of years, however. In the computer model of the study, this can trigger an ice age. With the silicate weathering alone, we were unable to simulate such extreme values,” explains Dominik Hülse.

Ancient Ice Ages and Atmospheric Oxygen

The study shows that lower oxygen concentrations in the atmosphere, which occurred in the geological past, could have triggered stronger nutrient feedbacks, and thus have caused the extreme ice ages of early Earth history.

As humans today add more CO₂ into the atmosphere, the planet will continue to warm. But according to the scientists’ model, it could lead again to a cooling overshoot in the long run. However, the next event will likely be milder, because today’s atmosphere contains more oxygen than in the distant past, which dampens the nutrient feedback.

“At the end of the day, does it really matter much if the start of the next ice age is 50, 100, or 200 thousand years into the future?” asks Ridgwell. “We need to focus now on limiting ongoing warming. That the Earth will naturally cool back down is not going to happen fast enough to help us out.”

In the next step, Hülse wants to use the model to understand why the Earth System has, at times, recovered surprisingly quickly from past climate perturbations, and how interactions with the marine sediments contributed to this.

Reference: “Instability in the geological regulation of Earth’s climate” by Dominik Hülse and Andy Ridgwell, 25 September 2025, Science.
DOI: 10.1126/science.adh7730

The study was funded in part by the MARUM-based Cluster of Excellence “The Ocean Floor – Earth’s Uncharted Interface.”