admin
Global warming is usually framed as a one-way trajectory toward ever hotter conditions, but new research suggests Earth’s climate may be capable of swinging much further than expected, even far enough to trigger a future ice age. Scientists at the University of California, Riverside, say they have identified a missing piece in how Earth recycles carbon, one that helps explain why some ancient cold periods were so extreme.
For decades, scientists believed that Earth’s climate was regulated by a slow but steady natural balancing act driven by rock weathering. This process was widely seen as a dependable thermostat, gradually correcting temperature shifts over millions of years and preventing the planet from drifting too far toward either intense heat or deep cold. That view, the UC Riverside team argues, is incomplete.
How rock weathering cools the planet
The long-standing model centres on the interaction among rain, rocks and carbon dioxide. As rain falls, it absorbs CO₂ from the atmosphere. When that rainwater flows over exposed land, it chemically reacts with rocks, especially silicate rocks such as granite, slowly breaking them down.
The dissolved rock material and captured carbon are then washed into the oceans. There, carbon combines with calcium released during weathering to form shells and limestone reefs. Over time, these materials settle onto the seafloor, locking carbon away for hundreds of millions of years and lowering atmospheric CO₂ levels.
“As the planet gets hotter, rocks weather faster and take up more CO₂, cooling the planet back down again,” says Andy Ridgwell, UCR geologist and co-author of the paper published in Science in September 2025. This feedback has long been viewed as Earth’s natural climate stabiliser.
Why ancient ice ages defy expectations
But the geological record reveals periods when this stabilising mechanism appears to have failed. Some of Earth’s earliest ice ages were so severe that glaciers and snow spread across nearly the entire planet. Such conditions, the researchers argue, cannot be explained by a climate system that simply self-corrects in small increments.
That contradiction led the team to search for an additional mechanism, one capable of pushing Earth’s climate beyond gentle regulation and into dramatic extremes.
Story continues below this ad
Oceans, nutrients and a runaway feedback loop
The missing factor, they say, lies in how carbon is buried in the ocean and how that process interacts with nutrients and oxygen. As atmospheric CO₂ rises and the planet warms, increased rainfall washes more nutrients, particularly phosphorus, into the oceans. These nutrients stimulate blooms of plankton, microscopic organisms that absorb carbon dioxide through photosynthesis.
When plankton die, they sink to the seafloor, taking the carbon they absorbed with them. In this way, carbon is transferred from the atmosphere to ocean sediments.
Under warmer conditions, however, this system changes. More plankton growth means more decaying organic matter, which reduces oxygen levels in the ocean. With less oxygen present, phosphorus is more likely to be released back into the water rather than permanently buried. That recycled phosphorus fuels even more plankton growth, whose decay further depletes oxygen, keeping nutrients and carbon cycling through the system.
As this feedback loop intensifies, increasingly large amounts of carbon are buried. Eventually, atmospheric CO₂ drops sharply, and global temperatures begin to fall.
Story continues below this ad
When climate regulation overshoots
Rather than gently restoring balance, this feedback can overshoot. In computer simulations run by the researchers, the cooling effect became strong enough to push Earth into an ice age.
Ridgwell compares the process to a household cooling system that works unevenly. “In summer, you set your thermostat around 78°F. As the air temperature climbs outside during the day, the air conditioning removes the excess heat inside until the room temperature comes down to 78°F, and then it stops,” he says.
Earth’s climate control, he explains, isn’t broken but it may not always respond smoothly. “It’s more like the thermostat isn’t positioned right next to the air conditioner,” allowing the system to overcorrect.
Why today’s world may respond differently
The study also offers an explanation for why ancient ice ages were so intense. Early in Earth’s history, oxygen levels in the atmosphere were much lower. That made the nutrient-driven feedback in the oceans far stronger and far less stable.
Story continues below this ad
Today, oxygen levels are significantly higher, weakening that feedback loop. As human activity continues to add CO₂ to the atmosphere, the planet is expected to keep warming in the near term. Over much longer timescales, the researchers’ model suggests that cooling will eventually follow, but likely in a less extreme form.
Also Read: A ‘warm ice age’ may have permanently changed Earth’s climate cycles
Ridgwell likens modern conditions to “placing the thermostat closer to the AC unit.” Even so, the model indicates that long-term cooling could still arrive sooner than previously expected, potentially bringing forward the beginning of the next ice age by tens or even hundreds of thousands of years.
Why climate action still matters
Despite this distant possibility, the researchers stress that it does nothing to offset the urgent problem of present-day warming.
Story continues below this ad
“At the end of the day, does it matter much if the start of the next ice age is 50, 100, or 200 thousand years into the future?” Ridgwell says. “We need to focus now on limiting ongoing warming. That the Earth will eventually cool back down, in however wobbly a way, is not going to happen fast enough to help us out in this lifetime.”
In other words, Earth’s climate may eventually swing back toward cold, but not before humans experience the full consequences of the warming now underway.
