What sounds like science fiction is the result of a recent study by researchers from the University of Bremen and the University of California. According to them, Earth could one day cool itself as a result of the current and ongoing warming – thereby initiating a new ice age.
Ice Age: When Warmth Leads to Cold
For billions of years, Earth has oscillated between heat and cold. The climate is normally regulated by a natural process: the weathering of rocks. “When the planet warms, rocks weather faster and absorb more CO2, allowing the Earth to cool down again,” explains researcher Dominik Hülse from MARUM – Center for Marine Environmental Sciences, in a statement (via EurekAlert). Rain absorbs CO₂ from the atmosphere, dissolving silicates and flushing the bound carbon into the oceans. There, limestone forms, storing the carbon for millions of years.
However, the new study shows that an additional mechanism is hidden in the sea that can overcool Earth, meaning beyond the necessary point. As CO₂ levels rise, more nutrients like phosphorus enter the water. This allows algae to grow, which bind carbon. When these in turn die, they sink to the seabed, taking the carbon with them. At the same time, warmer oceans lose oxygen, leading to phosphorus recycling. This cycle reinforces itself: More algae mean more oxygen consumption, which in turn releases more nutrients.
In short, more and more carbon accumulates in the sediments until temperatures drop drastically. “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,” Hülse explains. “In the computer model of the study this can trigger an ice age,” he adds.
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“We Need to Focus Now”
Ridgwell compares this effect to a thermostat that overreacts. “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 explains to Earth.com. However, Earth’s thermostat is subject to fluctuations. “It might not be in the same room as the air conditioning unit, making performance uneven,” he added. Thus, Earth’s climate system could also overshoot its target and, instead of stabilizing, tip into the next ice age.
At first glance, it sounds comforting that Earth regulates itself. But researchers warn that this natural correction would be far too slow to stop today’s climate crisis. Ridgwell clarifies: “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.” Even if the process were to occur, according to the model, it would be significantly weakened by today’s higher oxygen content in the atmosphere.
Research reminds us that Earth’s climate rarely remains in balance. In the deep past, similar feedbacks triggered massive ice ages that wiped out almost all life while also enabling new evolutionary developments. The current study shows that these mechanisms are still at work in the background today. But while past ice ages took millions of years, the current temperature increase due to human activity is progressing at record speed.
Sources: “Instability in the geological regulation of Earth’s climate” (Science, 2025); MARUM, Earth.com
This article was translated with the help of AI and carefully reviewed by our editorial team.