Bremen, Germany, September 26, 2025 – A groundbreaking study published in Science reveals a critical missing piece in understanding Earth’s carbon cycle and its role in long-term climate regulation, suggesting that global warming could trigger an overcorrective cooling, potentially plunging the planet into an ice age over hundreds of thousands of years. Conducted by Dr. Dominik Hülse from MARUM – Center for Marine Environmental Sciences at the University of Bremen and Dr. Andy Ridgwell from the University of California, Riverside, the research introduces an advanced Earth system model that highlights nutrient-driven feedback loops as a key driver of extreme climate shifts, including the snowball Earth events of the distant past.
Background: Unraveling Earth’s Climate Regulation
Amid human-driven climate change, scientists are racing to understand the processes that have historically stabilized Earth’s climate. Traditionally, silicate rock weathering has been considered the primary mechanism: Rain absorbs atmospheric carbon dioxide (CO?), dissolves exposed rocks, and transports carbon and calcium to the ocean, where it forms shells and limestone reefs, locking carbon away for millions of years. “When the planet warms, rocks weather faster, absorbing more CO? and cooling the Earth,” explains Hülse. 0 However, this process alone cannot explain extreme cooling events, such as the snowball Earth phases when the planet was entirely covered in ice and snow.
Study Methodology: A Refined Earth System Model
Hülse and Ridgwell have spent years refining a computational Earth system model, integrating previously overlooked processes. Their latest model, detailed in Science, incorporates nutrient dynamics, particularly phosphorus, and their impact on marine ecosystems. The study simulates how increased CO? and warming drive nutrient runoff into oceans, fueling algal growth that sequesters carbon during photosynthesis. When algae die, they sink to the ocean floor, burying carbon in sediments. However, in a warmer world, oxygen depletion in oceans recycles phosphorus back into the water, creating a feedback loop: more nutrients spur more algal growth, consuming more oxygen, recycling more nutrients, and burying more carbon—ultimately cooling the planet.
The model was tested against geological records, focusing on periods with low atmospheric oxygen, common in early Earth history, which amplified these nutrient feedbacks and triggered extreme cooling. The researchers also projected future scenarios under current CO? emissions to assess long-term climate impacts.
Findings: A Tipping Point Toward Ice Ages
The study’s key revelation is that the Earth system doesn’t always stabilize gently after warming. Instead, nutrient-driven feedbacks can overcorrect, driving temperatures far below baseline levels over hundreds of thousands of years. Key findings include:
- Nutrient Feedbacks: Increased phosphorus in oceans, spurred by warming, boosts algal blooms, which bury significant carbon in sediments, reducing atmospheric CO? and cooling the planet.
- Oxygen’s Role: Low oxygen levels, as seen in early Earth, intensify nutrient recycling, amplifying cooling. Today’s higher oxygen levels would dampen this effect, but not eliminate it.
- Snowball Earth Explanation: The model successfully simulates extreme ice ages, unlike silicate weathering alone, which couldn’t replicate such drastic shifts.
- Future Implications: Current CO? emissions will warm the planet for millennia, but in roughly 100,000 years, a cooling overcorrection could occur, though less severe due to modern oxygen levels.
Health and Environmental Implications
While the prospect of an ice age lies far in the future, the study underscores the fragility of Earth’s climate regulation. Human-driven CO? emissions are disrupting these natural feedbacks, risking unpredictable long-term consequences. “The question isn’t whether an ice age starts in 50,000 or 200,000 years,” Ridgwell notes. “We need to focus on limiting warming now—Earth’s self-cooling won’t save us fast enough.” 0 The research aligns with broader concerns about climate tipping points, such as permafrost thaw or ocean acidification, which could exacerbate nutrient cycles and destabilize ecosystems.
Conclusions and Future Directions
The study, supported by MARUM’s Excellence Cluster “The Ocean Floor – Earth’s Unexplored Interface,” highlights the ocean’s pivotal role in climate dynamics. Starting January 2026, Hülse plans to use the model to explore why Earth historically recovered rapidly from climate perturbations, focusing on organic-sediment interactions. 0 The findings call for:
- Urgent Emission Cuts: Mitigating CO? to prevent long-term climate destabilization.
- Enhanced Modeling: Integrating nutrient and oxygen dynamics into global climate models.
- Public Awareness: Educating policymakers on the ocean’s role in climate regulation.
Public and Scientific Relevance
This discovery reframes our understanding of Earth’s climate resilience, warning that natural systems could amplify human impacts in unforeseen ways. It’s a call to action for scientists, policymakers, and the public to prioritize sustainable practices to avert catastrophic climate shifts—whether warming now or cooling in the distant future.
Source: Hülse D, Ridgwell A. Instability in the geological regulation of Earth’s Climate. Science (2025). DOI: 10.1126/science.adh7730.
Additional Resource: University of California News Release.
