For decades, scientists have described Earth’s climate as governed by a slow but steady self-regulating system. This natural thermostat is built on rock weathering: rainwater absorbs carbon dioxide from the air, reacts with exposed rocks like granite, and washes dissolved minerals into the oceans. There, carbon combines with calcium to form seashells and limestone, which eventually settle on the ocean floor, locking carbon away for millions of years. This cycle, scientists believed, acted as a gentle hand on the climate, keeping Earth from overheating or freezing.
But new research from UC Riverside suggests that this picture was incomplete. Their study reveals another powerful mechanism in Earth’s carbon cycle, one that doesn’t just nudge the planet back to balance but could instead cause it to overshoot—plunging Earth into a deep freeze.
The Unexpected Power of Plankton
The missing piece, according to the researchers, lies in how the oceans bury carbon. As carbon dioxide levels in the atmosphere rise and the planet warms, more nutrients such as phosphorus are flushed from land into the sea. These nutrients feed blooms of plankton—tiny, photosynthetic organisms that take in CO₂ as they grow. When plankton die, they sink to the seafloor, carrying that carbon with them. Over long timescales, this burial removes massive amounts of carbon from circulation, cooling the planet.
At first glance, this seems like another stabilizing process. But the UC Riverside team found that in warmer conditions, the oceans start to lose oxygen. This lack of oxygen disrupts the burial of phosphorus, allowing it to be recycled back into the water. The recycled nutrients fuel yet more plankton growth, whose decay consumes even more oxygen. The cycle repeats, accelerating until vast amounts of carbon are buried at once. Instead of gently cooling the planet, the system overshoots, pulling Earth far below its starting temperature.
The result? A mechanism powerful enough to tip Earth into an ice age.
Lessons from a Frozen Past
Geological records show that Earth has indeed gone through extreme “snowball” ice ages in its distant past, when the entire surface may have been covered in ice and oceans sealed under frozen sheets. These events were too intense to be explained by rock weathering alone, and the UC Riverside findings provide a convincing missing link.
The team’s computer models suggest that this nutrient-driven carbon burial system could explain why Earth’s climate sometimes swings so dramatically. The analogy offered by Andy Ridgwell, a geologist and co-author of the study, makes the concept vivid: imagine a thermostat cooling a house. Normally, it turns the air conditioning on until the room returns to the desired temperature and then stops. But what if the thermostat were placed in a different room than the AC unit? The system would overcompensate, chilling the house more than intended.
In Earth’s case, the “misplaced thermostat” is the complex interaction between warming, nutrient recycling, and oxygen levels in the ocean.
Why the Past Was More Extreme
One important detail lies in atmospheric oxygen. In ancient times, oxygen levels were lower than they are today. With less oxygen available, the feedback loop of nutrient recycling and carbon burial was more erratic, making the thermostat overshoot wildly. This explains why Earth’s earlier ice ages were so extreme.
Today, with higher oxygen levels, the system is more stable. If an overshoot happens again in the future, it is likely to be less severe than in the past. Still, it could be strong enough to bring forward the beginning of the next ice age, a reminder that even Earth’s natural defenses against warming can come with sharp consequences.
What This Means for Our Future
In the short term, the overwhelming trend is still warming. Human activity is pumping billions of tons of CO₂ into the atmosphere every year, raising global temperatures, melting ice, and destabilizing ecosystems. The natural carbon cycle works on timescales of tens to hundreds of thousands of years—far too slow to counteract the rapid changes we are causing today.
The UC Riverside study shows that, eventually, Earth’s climate will swing back, perhaps overshooting into cooling. But this rebound is not a solution to the current crisis. It will not arrive quickly enough to offset the damages of warming in our lifetimes or those of many future generations.
As Ridgwell puts it, whether the next ice age begins in 50,000 years or 200,000 years makes little difference to us now. What matters is how we respond to the pressing reality of today’s warming world.
A Planet Always in Motion
This discovery reframes our understanding of Earth’s climate as something far less delicate than once thought. Instead of a quiet balance, the planet’s thermostat is a dynamic, sometimes unruly system capable of dramatic swings. It explains ancient frozen worlds and reminds us that climate stability cannot be taken for granted.
Yet, it also underscores a crucial truth: while Earth has natural ways of regulating carbon, those mechanisms operate on geological timescales, not human ones. For us, the choice is clear. We must act now to reduce emissions, protect ecosystems, and limit the damage of warming. The planet may cool itself eventually—but not in time to save us from the consequences of inaction.
The Story Still Unfolds
The UC Riverside team’s findings add a striking new chapter to the story of Earth’s climate. They reveal how profoundly interconnected land, sea, atmosphere, and life are in the great cycles that shape our world. They show us that Earth’s thermostat is powerful, but not always precise.
And perhaps most importantly, they remind us that while the planet’s climate machine will keep turning long after we are gone, the choices we make today will shape the lives of countless generations before that machine resets itself. The question is not whether Earth will recover—it always has—but whether humanity can thrive long enough to see what comes next.
More information: Dominik Hülse et al, Instability in the geological regulation of Earth’s climate, Science (2025). DOI: 10.1126/science.adh7730. www.science.org/doi/10.1126/science.adh7730
