Could Earth be on the brink of a dramatic climate reset? Recent research suggests that our planet might react to the overwhelming amounts of carbon dioxide (CO2) emitted by humans by ‘overcorrecting’ the existing climate imbalance, potentially triggering the next ice age sooner than previously projected. Instead of delaying this significant shift by tens of thousands of years, as scientists had once believed, it seems that natural processes might kick in much sooner than expected.
This revelation is linked to a remarkable new discovery: a kind of natural ‘thermostat’ capable of burying vast amounts of carbon deep beneath the seafloor with incredible efficiency. Researchers assert that this mechanism could eliminate anthropogenic carbon emissions within a span of 100,000 years.
Andy Ridgwell, a co-author of the study and geology professor at the University of California, Riverside, explained to Live Science that if both natural thermostats—namely, the silicate weathering feedback and the newly identified organic carbon burial—function together, we could very well witness the initiation of the next ice age as originally scheduled, instead of postponed by climate change.
However, it's crucial to note that this newly uncovered thermostat does not shield current generations from the adverse effects of global warming, as Dominik Hülse, a co-author from the University of Bremen, emphasizes. "Let’s be clear: we are not going to escape the repercussions of climate change in the next 100 or even 1,000 years," he stated, highlighting an important distinction about the challenges we are likely to face moving forward.
Experts have long theorized about Earth's ability to self-regulate its climate through geological timescales. This concept ties back to the 1980s when scientists suggested a process known as the silicate weathering feedback. This phenomenon occurs when rainfall captures CO2 from the atmosphere and interacts with silicate rocks, which comprise about 90% of the Earth’s crust. Here’s how it works: the CO2 reacts with the rocks, dissolving them and forming new molecules that eventually wash into the ocean. Once in the sea, these compounds contribute to the formation of limestone and chalk, effectively sequestering carbon for millions of years.
Much like how a thermostat operates, an increased concentration of CO2 in the atmosphere leads to a rise in Earth’s temperatures, thereby intensifying the water cycle. This cycle results in increased precipitation, subsequently accelerating silicate weathering. As a consequence, more atmospheric CO2 is transferred to the ocean, which helps bring CO2 levels down to normal background levels.
It’s worth mentioning that this feedback mechanism can also reverse. Ridgwell explains that if temperatures dip too low and CO2 levels fall, the thermostat might not trap enough CO2. Since CO2 is continuously emitted from the Earth's mantle through volcanic activity, this resulting deficit causes atmospheric CO2 to gradually rise back to baseline levels.
Nevertheless, silicate weathering operates at a sluggish pace, requiring up to one million years to restore balance after disturbances. Thus, it struggles to clarify certain significant climatic events, including the glacial and interglacial cycles, which involve dramatic fluctuations in CO2 and temperature approximately every 100,000 years.
Silicate weathering fails to account for extreme climate scenarios like the so-called snowball Earth events, which historically enveloped our planet in ice. If this was the sole mechanism maintaining Earth’s climate, its slow and steady balancing action would likely prevent such drastic fluctuations, as Hülse explains.
The introduction of a second ‘thermostat’
The inspiration for this groundbreaking research stemmed from Hülse's doctoral thesis, where he analyzed the quantities of organic carbon preserved in ocean sediments during various historical climate events. His findings illustrated how periods of heightened volcanic activity and warming led to the deposition of significant organic carbon quantities on the seafloor, hinting at a possible correlation between atmospheric CO2 levels and organic carbon burial in ocean sediments.
As Ridgwell noted, "There have undoubtedly been periods in Earth's history where vast amounts of organic carbon were deposited. We’ve long suspected that additional factors must be at play beyond just silicate weathering, but modeling this complexity poses a significant challenge."
Together, Hülse and Ridgwell took on the task of combining their research efforts into a singular global climate carbon cycle model which incorporated the burial of organic carbon on the ocean floor. Their collaboration unveiled a second natural thermostat linked to Earth’s phosphorus cycle. This cycle initiates when phosphorus-containing rocks, such as apatite, undergo weathering due to precipitation. The phosphorus then seeps into the ground, flowing through rivers and streams, ultimately reaching the ocean.
Phosphorus serves as an essential nutrient for microscopic photosynthetic organisms called phytoplankton, which utilize it for various life-sustaining processes. When phytoplankton perish, they sink to the ocean floor, depositing organic carbon, phosphorus, and other nutrients.
In a warming climate, increased phosphorus runs into the ocean, stimulating phytoplankton growth. This in turn means more organic carbon and phosphorus settle at the seafloor. However, one of the challenges is that warmer oceans are also less capable of holding oxygen, leading to a process where oxygen is less soluble at higher temperatures. This condition causes previously deposited phosphorus to be released back into the water column while organic carbon remains trapped in sediments.
Ridgwell pointed out, "While the precise mechanisms are not fully understood, we know this process takes place. Historical events show that, after warming periods, when large quantities of organic carbon are buried, the phosphorus content of that material is remarkably low compared to normal conditions. If it’s not being buried, then that phosphorus is likely being recycled back into the ocean."
As phosphorus returns to circulation, it re-enters the food web, allowing phytoplankton populations to flourish as they feast on phosphorus from both terrestrial and marine sources. This leads to an explosion in phytoplankton numbers, which efficiently absorbs atmospheric CO2 and sequesters more organic carbon within the ocean depths, ultimately cooling the planet.
Thus, as the planet heats up, ocean productivity surges, more carbon can be sequestered, and this process aids in reducing global temperatures. A significant distinction between phosphorus dynamics and silicate weathering is that phosphorus levels in oceans do not immediately decline when cooling occurs, as there continues to be a release of phosphorus from the seafloor.
As Ridgwell explains, "The organic carbon thermostat can be compared to the silicate system, but with an added boost. You accumulate so many nutrients in the ocean, and because they are recycled so efficiently, it becomes very challenging to deplete them."
The phosphorus cycle is designed to eventually restore balance, but in the interim, it has the potential to cause Earth to ‘overcorrect’ during tumultuous fluctuations, possibly leading to snowball Earth scenarios. While the exact response of this second thermostat to climate change remains uncertain, researchers believe that the ocean’s current oxygen levels are significantly higher than during prior epochs, making a snowball Earth scenario unlikely.
In fact, there is a possibility that the organic carbon thermostat could compensate for the delay in the onset of the next ice age. Climate change is indeed disrupting Earth's natural cycles—previous research indicated that human emissions could postpone the expected arrival of the next glacial phase, currently forecasted for about 11,000 years from now, by tens of thousands of years. Yet, if the organic carbon thermostat is engaged, atmospheric CO2 levels might revert to natural background levels more expeditiously, allowing the next ice age to commence as originally expected.
"Regardless of the delay we might experience for the next ice age… considering this mechanism may push its onset forward again," Ridgwell remarked. "At some point, the next ice age will occur; it’s simply a matter of how soon it starts."
This is an exciting and complex topic that calls for further exploration and understanding. How do you feel about these findings? Do you agree or disagree? Let's discuss your thoughts in the comments below!
Sascha is a staff writer at Live Science, based in the U.K. She earned her bachelor's degree in biology from the University of Southampton and holds a master’s in science communication from Imperial College London. Her work has been featured in The Guardian and the health website Zoe. When not writing, she enjoys playing tennis, baking bread, and hunting for unique finds in second-hand shops.
