University of St Andrews researchers identify process behind past ice ages

Researchers at the University of St Andrews published findings Oct. 24, 2026, in Journal of Climate about a process not known before that could have helped push Earth into past ice ages, Astrobiology Web reported.

Natural orbital cycles started the spread of large ice sheets across the Northern Hemisphere, but how that growth led to Southern Ocean changes and carbon dioxide drawdown was not understood, according to Astrobiology Web. Because the areas are distant, scientists had long struggled to make that connection. The outlet reported that the paper identifies ocean circulation and sea ice as the connection lowering atmospheric carbon dioxide. Previous work indicated that most past ice ages resulted from greater carbon dioxide storage in the ocean, and that changes around Antarctica drove much of that storage.

The paper proposes that expanding Northern Hemisphere ice sheets cool waters in the nearby North Atlantic, Astrobiology Web reported. Those waters then flow toward the Southern Ocean, and if the circulation is strong enough, it triggers changes that store more carbon dioxide there. Researchers described this chain as the route from Northern Hemisphere ice sheets to Southern Ocean carbon drawdown.

Astrobiology Web reported that researchers ran ocean model simulations cooling only the far northern latitudes to represent a large ice sheet, then compared that result with a simulation of cooling the whole planet. In the northern-only case, the model generated nearly the same carbon dioxide drawdown, 74%, as the planetary cooling simulation.

The outcome supports the idea that expanding ice sheets chill northern waters which then move south and cause changes in the Southern Ocean, Astrobiology Web reported. Those changes helped drive Earth into past ice ages. The findings add support to the view that ice sheets across the Northern Hemisphere can affect conditions in the Southern Ocean and play a part in initiating past ice ages.

Dr Madison Shankle, the study‘s lead author, said the work demonstrates a mechanism found in models that connects Northern Hemisphere ice sheets to Southern Hemisphere ocean shifts lowering atmospheric carbon dioxide, according to Astrobiology Web. Shankle works in the School of Earth and Environmental Science. She called it a demonstration of a once-tricky link in ice-age theory using model simulations.