Scientists have uncovered a vital missing link in Earth’s carbon cycle that could finally explain how past ice ages occurred. The discovery highlights how warming conditions can ironically set off processes that push the planet into far colder climates than before.
According to researchers from the University of California, Riverside, when Earth warms, rainfall and runoff from land carry large amounts of nutrients into the oceans. These nutrients fuel massive plankton blooms. When plankton die, they sink to the seabed, burying large quantities of carbon and gradually reducing atmospheric CO₂ levels.
However, the team found that in low-oxygen ocean environments, this cooling feedback becomes significantly stronger. As plankton decay further reduces oxygen, it accelerates phosphorus recycling in seawater. This recycled phosphorus fuels even more plankton growth, allowing vast amounts of additional carbon to be buried. Over time, the process can dramatically cool the planet — powerful enough to trigger ice ages, where most of Earth becomes covered in snow and ice.
Computer simulations conducted by the researchers revealed that this effect may have contributed to some of the most extreme climate phases in Earth’s history, particularly when atmospheric oxygen levels were lower, such as during the planet’s early years.
Until now, scientists believed that rock weathering was the primary natural mechanism controlling Earth’s climate by absorbing CO₂ from the atmosphere. However, ancient ice age evidence did not fully fit this explanation. The newly identified ocean nutrient feedback system helps fill that gap, showing how climate shifts can become far more intense than previously understood.
Lead researcher Professor Ridgwell compared the phenomenon to a thermostat that sometimes “over-cools” the planet. While warming initiates the process, the feedback system can push Earth into an extreme cooling spiral.
Despite this discovery, scientists emphasise that it will not offset modern climate change. Human-driven greenhouse gas emissions are warming the planet much faster than such natural cooling cycles can operate. Researchers stress that immediate reductions in CO₂ emissions remain critical to prevent severe climate consequences.