ANTARCTICA — A study published in Nature Geoscience indicates that Antarctica’s ice sheet underwent a change approximately one million years ago, becoming more responsive to shifts in Earth's climate. The research shows the ice sheet shifted into a more sensitive state after the Mid-Pleistocene Transition, a major climate shift during which ice ages became longer, colder, and more intense.

Researchers used an advanced paleoclimate simulation developed at the IBS Center for Climate Physics (ICCP) at Pusan National University in South Korea to reconstruct global climate patterns over the past 3 million years. That simulation provided temperature and precipitation data that were input into the Penn State University ice-sheet-ice-shelf model, which tracks changes in ice sheet movement, thickness, temperature, and elevation across Antarctica and the Northern Hemisphere, including floating ice shelves in the Ross and Weddell Seas.

The simulations revealed that Antarctica entered a different mode of behavior after the Mid-Pleistocene Transition. Scientists identified a key atmospheric carbon dioxide threshold of approximately 240 parts per million, below which Antarctic ice volume responded more dramatically to changes in atmospheric and ocean temperatures.

"After this transition, the Antarctic ice sheet reacts much more strongly to changes in climate forcing. This indicates that the system does not evolve gradually but instead becomes more responsive after crossing a particular threshold in the climate system." said Dr. Kyung-Sook Yun, researcher at the IBS Center for Climate Physics and lead author of the study.

According to the study, colder ocean temperatures during ice ages reduced melting beneath portions of the Antarctic ice sheet that extend below sea level. At the same time, global sea levels were approximately 50–100 meters lower than present-day levels, which reduced pressure on the bedrock beneath ice shelves. That allowed the land underneath to slowly rise, supporting additional thickening of coastal ice. "Our findings suggest that the Antarctic ice sheet was more sensitive to external forcings than previously assumed. This also raises important questions about its future response to global warming." said Prof. Axel Timmermann, Director of the IBS Center for Climate Physics and co-author of the study. The study suggests that ice sheets may not respond to climate change in a slow, predictable manner but can shift abruptly into a more sensitive state after crossing critical climate thresholds.