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For decades, scientists believed that the climate of our planet is controlled by the process of weathering of rocks. This mechanism works as follows: rainfall absorbs carbon dioxide from the atmosphere and falls onto land. Water breaks down rocks, especially silicate ones like granite. The dissolved substances, including CO₂, then enter the oceans.
In the ocean, carbon combines with calcium from the rocks, forming shells and limestone reefs. These formations settle on the ocean floor, trapping carbon for hundreds of millions of years, which gradually reduces the level of CO₂ in the atmosphere.
Geologist Andy Ridgwell, one of the authors of the study, noted that under conditions of rising temperatures, the planet heats up, and rocks weather faster, leading to greater CO₂ absorption, thereby cooling the climate.
It was previously thought that this process serves as a stabilizing factor, preventing excessive temperature fluctuations. However, geological data suggest that some ancient ice ages were so severe that ice and snow covered nearly the entire planet, which cannot be explained by a simple temperature regulation mechanism.
The researchers identified an additional mechanism related to carbon burial in the oceans. As CO₂ levels in the atmosphere rise and temperatures increase, runoff carries more nutrients, such as phosphorus, into the sea, promoting the growth of plankton—microscopic organisms that absorb carbon dioxide through photosynthesis.
When plankton die, they sink to the ocean floor, taking carbon with them. Thus, carbon is removed from the atmosphere and stored in oceanic sediments.
However, in warmer conditions, this system begins to change. Enhanced plankton growth can lead to a decrease in oxygen levels in the ocean. With less oxygen, phosphorus is more likely to return to the water instead of being permanently buried. This phosphorus, in turn, promotes even more plankton growth, which further depletes oxygen upon decomposition.
This cycle continues, resulting in vast amounts of carbon being buried, and global temperatures begin to drop, often much more sharply than they initially rose.
Ridgwell compared this process to the operation of an air conditioner. “When you set the thermostat to 25°C, the air conditioner removes excess heat until the room temperature reaches the set point,” he explains.
The Earth’s climate system operates similarly but can respond unevenly, as if the thermostat were far from the air conditioner. Instead of stable temperature regulation, such feedback can lead to sharp cooling. In computer models, this effect has proven strong enough to trigger an ice age.
In the ancient atmosphere, oxygen levels were significantly lower, making the climate system less stable, which explains the severity of early ice ages.
Today, oxygen levels in the atmosphere are significantly higher than in the past, suggesting that future cooling will likely be less pronounced. Higher oxygen levels reduce the strength of feedback in the oceans.
“It’s as if the thermostat is now closer to the air conditioner,” Ridgwell added.
Nevertheless, this effect may be sufficient to accelerate the onset of the next ice age. However, this is not a reason for complacency.
“Ultimately, does it matter whether the next ice age occurs in 50, 100, or 200 thousand years? We need to focus on limiting current warming. The fact that the Earth will eventually cool, even if it happens unevenly, will not occur quickly enough to help us in our lifetime,” the scientist emphasized.
