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Scientists now believe intense global warming could paradoxically lead to a future ice age. Learn how an ocean feedback loop involving plankton can remove CO2 and cool the Earth.
It may seem strange, but scientists now believe that intense global warming could eventually lead the Earth into an ice age. Research from the University of California, Riverside, shows that the natural climate mechanisms that regulate Earth’s temperature do not always function as previously thought. Rather than maintaining a steady climate, these mechanisms might sometimes cause dramatic shifts between extreme conditions. The study was published in Science.
For many years, scientists believed Earth’s climate was kept in balance by a gradual natural process involving rocks, rain, and carbon dioxide. This process, called rock weathering, was thought to act like a reliable thermostat, preventing the planet from becoming either too hot or too cold.
How Rocks Help Cool the Planet
This process works in the following way. Rainwater absorbs carbon dioxide (CO₂) from the air as it falls. When this slightly acidic rain reaches the ground, it reacts with rocks, particularly hard ones like granite. Over time, the rocks gradually break apart.
As this happens, the carbon dioxide that was dissolved in the rain is carried away by rivers and eventually ends up in the oceans. There, it mixes with calcium released from the rocks to form shells and limestone. These materials settle on the ocean floor and store the carbon for millions of years. By removing CO₂ from the atmosphere, this process gradually cools the planet.
As explained by geologist Andy Ridgwell, one of the researchers, when the Earth warms, rocks break down more quickly and remove more carbon dioxide, which helps to cool the planet again.
A Problem with the Old Picture
Scientists know that some of Earth’s earliest ice ages were extremely severe, with ice sheets covering nearly the entire planet, turning it into what is sometimes referred to as a “snowball Earth.”
Such extreme freezing is difficult to explain if the climate system simply gently corrects itself. This led researchers to suspect that another powerful process might also be at work, one that can push the climate too far, rather than just maintaining balance.
The Role of Oceans and Tiny Life Forms
According to the new study, the missing link lies in the oceans. As the planet warms and carbon dioxide levels increase, more rainfall occurs, washing more nutrients from the land into the sea. One of the most important of these nutrients is phosphorus.
Phosphorus supports plankton, tiny organisms that live near the ocean’s surface. Plankton use sunlight and carbon dioxide to grow, similar to how plants do on land. When they die, they sink to the ocean floor, carrying the carbon they absorbed with them. This is another way carbon is removed from the atmosphere.
But this system has an unexpected twist. When plankton grow in large numbers, they can reduce oxygen levels in the water as they decay. Low oxygen makes it harder for phosphorus to remain buried in sea-floor sediments. Instead, it is released back into the water.
This recycled phosphorus then feeds even more plankton, which removes more carbon dioxide and further lowers oxygen levels. The cycle continues, feeding on itself. As more carbon is locked away, global temperatures begin to drop sharply.
What This Means for the Future
Rather than stabilizing the climate, this feedback loop can cause temperatures to drop far below their original level. In computer models used by the researchers, this effect was strong enough to trigger a full ice age.
In Earth’s distant past, oxygen levels in the atmosphere were much lower than they are today. This made the ocean’s nutrient cycle far more unstable, helping to explain why ancient ice ages were so extreme.
Today, oxygen levels are much higher, which weakens this runaway cooling effect. While human activity is clearly causing rapid global warming now, the researchers believe a natural cooling phase will eventually follow. However, it is unlikely to be as severe as the ice ages of the distant past.
Why Action on Climate Still Matters
Ridgwell emphasizes that this long-term cooling offers no comfort for modern society. Any natural drop in temperatures would take far too long to benefit people alive today. The urgent task remains the same: to limit human-caused warming now. Earth may eventually cool again, but it will do so slowly and unevenly, and not in time to prevent the impacts of climate change in our own lifetimes.
