New research suggests that cooling in the Northern Hemisphere may have triggered far-reaching ocean changes that helped drive Earth’s past ice ages.
Growing ice sheets in the Northern Hemisphere may have helped push Earth into past ice ages by triggering changes in ocean circulation thousands of miles away, near Antarctica. New research from the University of St Andrews identifies a possible mechanism connecting these distant regions, helping explain how the planet naturally reduced atmospheric carbon dioxide (CO2) as ice ages developed.
Scientists have long known that the Southern Ocean plays a central role in regulating atmospheric CO2. Changes in its circulation and sea ice can increase the amount of carbon stored in the deep ocean, contributing to the cooling associated with ice ages. But researchers have struggled to explain how expanding northern ice sheets could influence waters so far south.
How Northern Ice Sheets Could Transform the Southern Ocean
The growth of massive Northern Hemisphere ice sheets begins with changes in Earth’s orbit that alter how solar energy is distributed across the planet. According to the new study, published in the Journal of Climate, these expanding ice sheets may set off a much larger chain of events by cooling nearby North Atlantic waters.
As those colder waters move through the global ocean circulation system, they can eventually reach the Southern Ocean. If the northern cooling is strong enough, it could alter circulation around Antarctica and promote conditions that allow more CO2 to remain stored in the ocean rather than the atmosphere.
This proposed connection provides a physical explanation for how ice sheet growth in one hemisphere could help amplify cooling across the planet.
Ocean Simulations Reveal a Powerful Cooling Effect
To test the hypothesis, researchers used computer simulations that cooled only the ocean’s northernmost latitudes (mimicking the effect of a large ice sheet). They then examined whether the temperature changes could travel south and alter Southern Ocean conditions in ways that reduce atmospheric CO2.
The results showed that cooling northern waters alone produced a substantial response. The simulated reduction in atmospheric CO2 reached 74% of the reduction produced when the researchers cooled the entire planet.
The experiments support the proposed connection between Northern Hemisphere ice sheets and Southern Ocean carbon storage. However, they demonstrate that the mechanism is physically plausible in a model, rather than establishing exactly how much it contributed to individual ice ages in Earth’s past.
Rethinking What Drives Earth’s Ice Ages
Lead author Dr. Madison Shankle, from the University of St Andrews’ School of Earth and Environmental Science, explained:
“Essentially, we’ve produced evidence of a plausible mechanism connecting these two far-flung puzzles pieces – Northern Hemisphere ice sheets and Southern Hemisphere ocean circulation changes leading to CO2 drawdown – which has been a tricky thing to explain in our theory of Earth’s past ice ages. Our study takes the step of actually demonstrating them working in model simulations, which is a big step forward for this field.”
Ice age research has traditionally emphasized processes occurring around Antarctica, where ocean circulation strongly influences the exchange of carbon between the atmosphere and deep ocean. The new findings suggest that temperature changes in distant northern waters may also be an important part of that system.
Past ice ages provide natural examples of how carbon moves between Earth’s atmosphere and oceans over long periods. Understanding these processes can help scientists improve climate models and investigate how the global carbon cycle responds to changes in atmospheric CO2, including the additional carbon dioxide released by human activities.
Reference: “Isolated Northern Hemisphere Cooling in an Idealized Model Promotes Ocean Carbon Storage and Glacial-like Ocean Features” by Madison G. Shankle, Graeme A. MacGilchrist, Andrea Burke, Alice Marzocchi, Malte F. Jansen and James W. B. Rae, 22 October 2026, Journal of Climate.
DOI: 10.1175/JCLI-D-25-0355.1
Never miss a breakthrough: Join the SciTechDaily newsletter.
Follow us on Google and Google News.