This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: New research from the University of St Andrews has uncovered a previously unknown process that may have helped drive Earth into past ice ages. Published today (Oct. 22) in the Journal of Climate, the paper links ice sheets in the Northern Hemisphere to changes in ocean circulation and sea ice in the Southern Hemisphere understood to drive down atmospheric CO₂.
Linking these two key features of the ice ages has long been a challenge, given how far apart the two regions are. Earth was mainly driven into ice ages by more CO₂ being stored in the ocean, a process largely driven by changes in the Southern Ocean around Antarctica. Yet how the initial growth of large ice sheets in the Northern Hemisphere (brought about by natural cycles in Earth's orbit) then led to changes in the far-flung Southern Ocean that led to CO₂ drawdown was unknown.
This new paper proposes that once northern ice sheets start growing, they cool nearby North Atlantic waters, which eventually circulate all the way down to the Southern Ocean. If the cooling of the northern waters is strong enough, it could induce significant circulation changes in the south, of the sort known to lead to more CO₂ being stored in the ocean. Researchers tested this hypothesis in ocean model simulations by cooling only the far northern latitudes (mimicking the effect of a large ice sheet) and measuring whether it affected the Southern Ocean.
The results demonstrated that cooling the northern latitudes alone caused nearly the same amount of CO₂ drawdown (74%) as a simulation in which researchers cooled the entire planet. This result backs up the idea that ice sheets can cool northern waters that eventually make their way south and cause changes in the Southern Ocean—an important part of driving Earth into its past ice ages. Scientists studying ice ages have long focused on the Southern Ocean, and it's only recently that other remote parts of the ocean have started to be more appreciated.
Madison Shankle from the School of Earth and Environmental Science said, "Essentially, we've produced evidence of a plausible mechanism connecting these two far-flung puzzle 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." The ice ages are natural case studies of how carbon moves in and out of the atmosphere. The more researchers know about them, the more they can understand how Earth naturally moves carbon around in the carbon cycle.
This knowledge is critical in considering how the planet will respond to the added CO₂ within the Earth system today. Isolated Northern Hemisphere Cooling in an Idealized Model Promotes Ocean Carbon Storage and Glacial-like Ocean Features, Journal of Climate (2026). DOI: 10.1175/JCLI-D-25-0355.1 BA art history, MA material culture.
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