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Artistic representation of Snowball Earth. Credit: Song et al, 2023 DOI: 10.1038/s41467-023-37172-x
Our planet plunged into one of the most dramatic climate states in its long history, approximately 720–635 million years ago. During a period geologists call Snowball Earth, ice sheets crept from the poles all the way to the tropics, covering the oceans and continents in a nearly global freeze.
Evidence for this extreme climate comes from rock formations around the world that bear the signatures of ancient glaciers at low latitudes—signs that Earth's surface was encased in ice far beyond what we see in today's polar regions.
Scientists have long studied how a feedback process known as ice-albedo helped lock in and amplify this deep chill. Albedo is a measure of how much sunlight a surface reflects; snow and ice are bright and reflect most of the sun's energy back into space, cooling the planet further as more of it spreads across the surface.
But new research, published in Climate of the Past, explores another overlooked feedback: how salt emerging from sea ice could have played a role in enhancing Earth's icy grip during the earliest stages of global glaciation, when the planet was transitioning from a warmer climate into a fully frozen state.
Salt's climate effect
When sea ice forms today in polar regions, it does not freeze as pure water. Ocean water contains salt, and as the ice forms, most of the salt is squeezed out of the freezing lattice. Some of that salt stays trapped in brine pockets, and under very cold, dry conditions it can crystallize and precipitate out of the remaining ice.
On a Snowball Earth, the authors suggest this process may have been widespread across the vast expanse of bare sea ice exposed to the atmosphere.
As ice sublimates—turning directly from a solid into water vapor without melting—the salt that had been trapped in its structure would have been left behind as a residue of bright, white salt crystals on the surface. In a climate already dominated by high reflectivity, this saline crust could have boosted the planet's reflective power even more. In climate science terms, that's another positive feedback: more reflected sunlight means less warming, which means even more ice (and in this case salt) accumulating on Earth's frozen shell.
To explore how significant this effect might have been, researchers from UiT—The Arctic University of Norway built a simple climate model that included this salt-albedo feedback.
In their simulations, once the process set in, it helped to intensify the cooling trend that was already underway during the early stages of the Snowball Earth event. That suggests salt precipitation could have acted like an accelerator pedal, pushing the world deeper into a frozen state than it might have reached with ice-albedo processes alone.
Additionally, in the model, once the salt feedback is activated, returning to a warmer climate would require substantially more warming than in simulations without salt, suggesting the process could have made the frozen state more resistant to melting.
Illustration of the temperature and solar radiation modeling parameters influencing glaciation to hothouse transitions with and without salt deposits. Credit: Samuelsberg et al, 2026.
Why salt matters in climate models
Ocean salinity influences water density, circulation and how heat moves through the seas, all of which feeds back into the global climate system. Previous research has even shown that differences in salinity can change how easily a planet enters or exits a Snowball state.
Laboratory and field studies have shown that salty ice can have a very high albedo compared with ordinary ice or snow, but these effects haven't been widely incorporated into global climate models, especially those used to study Earth's deep past.
In practical terms, that means that many simulations of Snowball Earth may have underestimated just how reflective the planet's surface could have become once ice began to shed its salty residue. The new results suggest this overlooked process might help explain why Earth entered such a deep, prolonged freeze in the first place and how sensitive planetary climates can be to seemingly small physical processes acting at the surface.
However, the researchers stress that this is an initial modeling study. It remains uncertain whether large, long-lasting surface deposits of salt would have formed and persisted on Snowball Earth, and more detailed climate models are needed to test how strong this feedback would have been when processes such as clouds, wind and ice dynamics are included.
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The bigger picture of deep freezes
Snowball Earth events, while extreme, were not one-off curiosities. They are believed to have occurred more than once in the Neoproterozoic era (approximately 1,000–538 million years ago), a time of dramatic climatic swings that may also have influenced the evolution of early life. Understanding the precise mechanics of these events helps scientists unravel how Earth's climate system behaves under conditions vastly different from today's.
The salt-albedo feedback does not replace the classic ice-albedo feedback that climate scientists have long studied. Rather, it adds another layer to the complex interplay of processes that can tip a planet into (or out of) a global glaciation. As modelers refine their tools and include more detailed physics, we may find that Earth's ancient freeze was even more nuanced than rocks and simulations have previously shown.
Written for you by our author Hannah Bird, edited by Sadie Harley, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a donation (especially monthly). You'll get an ad-free account as a thank-you.
Publication details Aksel Samuelsberg et al, Amplified cooling of Snowball Earth from a salt–albedo feedback, Climate of the Past (2026). DOI: 10.5194/egusphere-2026-679 Journal information: Climate of the Past
Key concepts glaciation
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— Source: Phys.org (https://phys.org/news/2026-03-salt-snowball-earth-million-years.html)
