When the planet warms, rocks erode faster and absorb more CO₂, and algae grow faster, removing oxygen from the oceans and creating more nutrients for the algae — a powerful feedback loop that could trigger drastic cooling of the Earth.
Earth’s climate balance does not depend solely on the slow erosion of silicate rocks, a process that captures carbon and stabilizes temperature over geological eras.
According to a recent publication in Scienceos feedback loops biological and oceanic, especially involving algae, phosphorus and oxygen, can cause much more drastic variations in the planet’s temperature.
For much of Earth’s history, scientists considered the slow decay of silicate rocks to be the principal natural “thermostat”. of the planet.
In this process, the rainwater absorbs carbon dioxide (CO₂) from the atmosphere, it reaches exposed rocks and gradually dissolves them. The carbon and calcium released end up reaching the oceans, where they serve as raw material for shells and limestone reefs. These materials fix carbon at the bottom of the sea for hundreds of millions of years.
“When the planet heats up, rocks wear out more quickly and absorb more CO₂, allowing the Earth to cool down again,” he explains. Dominik Hülseresearcher at the University of Bremen, Germany, and first author of the study, at the Center for Marine Environmental Sciences at U.Bremen.
However, there was periods when the planet was completely frozencovered in ice from one pole to the other. The researchers emphasize that this phenomenon cannot be explained just due to the weathering of the rockswhich indicates that other forces were involved in these extreme coolings.
A crucial clue It’s in the way the ocean stores carbon. As atmospheric CO₂ concentrations increase and the planet warms, more nutrients, such as phosphorus, are washed out to sea.
These nutrients fuel bursts of algal growth, which capture carbon through photosynthesis. When algae die, they sink to the ocean floor, taking the carbon with them, explains .
In a warmer climate, however, the rapid growth of algae it also reduces oxygen levels in the water. With less oxygen availablephosphorus tends to be recycled instead of being retained in sediments.
This creates a powerful feedback loop: more nutrients generate more algae, which consume more oxygen when decomposing, releasing even more nutrients. At the same time, large amounts of carbon are trapped in marine sediments, which ends up cooling the planet.
For several years now, Hülse and the study’s co-author, Andy Ridgwelldevelop an advanced computer model of the Earth’s climate system that incorporates these complex interactions.
“This most complete model of the Earth System does not always stabilize the climate gradually after a warm-up phase; may, on the contrary, overcompensate and cool the Earth well below its initial temperaturea process that, however, could still take hundreds of thousands of years”, says Hülse.
“In the computer model used in our study, this mechanism could trigger an ice age. Only with the weathering of silicates we are unable to simulate such extreme values”, explains the researcher.
The results suggest that with lower oxygen levels in the atmosphere, as in Earth’s distant past, these nutrient cycles became stronger and could have been responsible for the severe ice ages that marked the beginnings of the planet’s geological history.
Today, with the human action adding more CO₂ to the atmospherethe planet will continue to warm. But, according to the scientists’ model, in the long term this could lead again to excessive cooling.
The next event, however, should be milderbecause the current atmosphere contains more oxygen than in the remote past, which mitigates the nutrient feedback effect.
“Ultimately, it will be so important if the start of the next ice age occurs from now on 50, 100 or 200 thousand years?“, asks Ridgwell. “What matters now is focus on limiting ongoing warming. The Earth’s natural cooling will not be fast enough to save us.”
