Overview: A Two-Thermostat View of Earth’s Climate
Scientists have long explored how Earth naturally regulates its climate on geological timescales. The classic model centers on the silicate weathering feedback: when the planet warms and rain increases, CO2 is drawn down through chemical reactions with silicate rocks, ultimately storing carbon in oceans and sediments. This slow mechanism has been described as a thermostat that gradually stabilizes atmospheric CO2 over hundreds of thousands to millions of years. New findings, however, point to a second, faster regulator that could dramatically alter how soon—or how late—the next ice age arrives.
The Emergence of a Second Thermostat: Organic Carbon Burial in the Seafloor
Researchers combined two lines of inquiry—organic carbon burial in ocean sediments and the phosphorus cycle on land—to build a global climate model. They found that during periods of warming, vast amounts of organic carbon can be deposited on the seafloor along with phosphorus. In warmer oceans, phytoplankton blooms thrive on the increased nutrient supply, accelerating carbon capture and transport to the deep sea. This creates a feedback loop that sequesters carbon more rapidly than previously thought.
What makes this “thermostat” special is its coupling with phosphorus. In warm conditions, more phosphorus reaches the ocean, fueling phytoplankton growth and, in turn, promoting sustained carbon burial. The result is a potentially powerful, self-reinforcing mechanism that can pull CO2 out of the atmosphere much faster than the silicate weathering feedback alone.
Implications for the Next Ice Age
The study suggests that if this organic carbon thermostat operates as described, the clock for the next glacial period could reset to an earlier date than previously projected. Traditionally, scientists estimated a next ice age might have been delayed by tens of thousands of years due to human-caused warming. The new mechanism could offset that delay, nudging the timing back toward a more immediate cycle around 11,000 years from now, depending on how these feedbacks interact with ongoing climate change.
It’s important to stress that this does not imply humanity would be spared from warming in the near term. The organic carbon thermostat works on longer timescales and does not shield us from current temperatures or extreme weather. In fact, the interaction between these feedbacks and present-day emissions remains complex and uncertain.
Why This Matters for Climate Science
Until now, the silicate weathering thermostat has been the primary lens for understanding long-term climate stability. The discovery of a more rapid, phosphorus-linked carbon burial process adds nuance to that picture. It helps explain why Earth’s climate has behaved in bursts, with glacial and interglacial cycles roughly every 100,000 years, and why some extreme events like snowball Earth—where oceans freeze over completely—happen in Earth’s deep past despite the silicate feedback. The new model shows that Earth’s natural regulation is potentially more dynamic and multi-layered than a single thermostat would suggest.
What Researchers Said
Lead author Andy Ridgwell notes that the organic carbon thermostat is not a guarantee of a quick return to a cooler world. The balance of feedbacks, ocean oxygen levels, and nutrient cycling will determine the exact outcome. Co-author Dominik Hülse emphasizes that while historical cycles illuminate possible futures, today’s climate system is being perturbed in novel ways by human activity. The study frames a question worth pursuing: how will these natural thermostats respond to rapid, human-driven changes in greenhouse gas concentrations?
Looking Ahead
As scientists refine climate models, the possibility of an accelerated or altered ice-age timeline invites a broader discussion about long-term climate risk and planetary resilience. Whether or not the organic carbon thermostat reshapes the schedule of Earth’s climatic cycles, it underscores a key lesson: Earth’s climate is governed by interconnected, often counterintuitive feedbacks that operate across millennia—and that our best forecasts require embracing that complexity.
