Two Climatic Thermostats Regulating Earth’s Balance
Earth’s climate has long been understood to be moderated by natural feedbacks that act like thermostats. The well-known silicate weathering feedback is a slow, geological process: rain erodes silicate rocks, CO2 is drawn down to form carbonates in the ocean, and atmospheric CO2 levels drift back toward a balance over hundreds of thousands to millions of years. This mechanism helps explain how the planet dampens carbon imbalances and returns toward a baseline after perturbations.
However, a new study published in Science adds a second, faster mechanism—an organic carbon thermostat tied to the ocean’s phosphorus cycle. The researchers combined models of carbon burial in ocean sediments with insights from phosphorus dynamics to reveal a potential “supercharger” that could accelerate CO2 sequestration in the oceans.
The Organic Carbon Thermostat: A Fast-Track to Cooler Climates?
The core idea: during warmer periods, more weathering of phosphate-bearing rocks releases phosphorus into rivers and oceans. Phytoplankton—a key group of tiny marine plants—thrive on this phosphorus, driving a bloom that draws down substantial amounts of CO2 and deposits organic carbon and phosphorus onto the seafloor. Warmer oceans, which hold less oxygen, paradoxically promote this process by enhancing nutrient recycling, enabling a rapid sequestration of carbon. This creates a feedback loop that can cool the climate much faster than silicate weathering alone would allow.
Lead authors Ridgwell and Hülse describe this second mechanism as a “supercharged” version of the silicate thermostat. While the classic carbon-weathering loop tends to rebalance CO2 over up to one million years, the organic-carbon thermostat could shorten that timescale dramatically, potentially offsetting human carbon emissions on a geologic timetable of 100,000 years. This rapid burial of organic carbon might, in theory, help the atmosphere return to background CO2 levels sooner than previously anticipated.
Implications for the Next Ice Age
The timing of the next glacial period has long been debated. Some climate models predict a roughly 11,000-year cadence for ice-age cycles unless external factors intervene. By introducing a faster pathway to remove CO2, the new thermostat could delay or accelerate the onset of the next ice age, depending on how the processes balance over time. In their discussion, the researchers emphasize that this mechanism does not shield people from near-term warming. The rapid changes described operate on much longer geological timescales, while current climate impacts occur on decadal scales.
What This Means for Our Understanding of Climate Regulation
The study reframes how scientists view planetary climate control. Silicate weathering remains a crucial, slow regulator, but the organic-carbon and phosphorus interplay adds a dynamic that could respond more quickly to warming events. If future research confirms the magnitude and reliability of this pathway, models of past and future climate will need to account for a dual-thermostat system, with the potential for outcomes as varied as earlier snowball Earth events or timely ice-age transitions.
Context and Caution
Experts caution that while the organic-carbon thermostat is a compelling addition to the climate puzzle, it does not negate the risks of ongoing climate change. The researchers acknowledge uncertainties about how strongly this mechanism operates under current conditions and how it interacts with other global processes. The ocean’s oxygen levels and nutrient cycles are just part of a complex system that responds to, but does not automatically fix, human emissions.
What Comes Next?
Further research is needed to quantify the exact strength and timing of the organic-carbon thermostat in modern oceans. If confirmed, this mechanism could refine our understanding of both Earth’s long-term climate trajectory and the potential timing of future ice ages, highlighting the planet’s remarkable, and sometimes surprising, capacity to regulate its own climate over deep time.
