The research, led by scientists at the IBS Center for Climate Physics (ICCP) at Pusan National University in South Korea, offers fresh insight into how massive ice sheets react to long term climate changes and what that could mean for future sea level rise.

Today, Antarctica contains the largest mass of ice on the planet and plays a major role in regulating global sea levels. Around one million years ago, Earth experienced a major climate transition in which ice ages became longer, colder, and more intense. Scientists refer to this period as the Mid-Pleistocene Transition. Although researchers have known about this shift for decades, exactly how Antarctica's ice sheet responded has remained uncertain.

Simulating 3 Million Years of Climate History

One of the biggest obstacles has been the lack of realistic long term climate records needed to test ice sheet behavior under ancient conditions.

To solve this problem, the team used an advanced paleoclimate simulation recently developed at the ICCP that reconstructs global climate patterns over the past 3 million years. The simulation provided detailed temperature and precipitation data, which researchers fed into the Penn State University ice-sheet-ice-shelf model.

That model tracks changes in ice sheet movement, thickness, temperature, and elevation across Antarctica and the Northern Hemisphere. It also simulates the behavior of floating ice shelves, including those in the Ross and Weddell Seas.

Using one of South Korea's most powerful supercomputers dedicated to basic science research, the team produced a physically consistent picture of how Earth's major ice sheets evolved as climate conditions changed over time.

Antarctic Ice Reached a Critical Threshold

The simulations revealed that Antarctica entered an entirely different mode of behavior after the Mid-Pleistocene Transition.

Researchers identified a key atmospheric carbon dioxide threshold of roughly 240 parts per million. Once CO2 levels dropped below that point, Antarctic ice volume began responding much 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.

Why Antarctica's Ice Expanded So Rapidly

According to the simulations, several processes worked together to accelerate Antarctic ice growth after the climate transition around one million years ago.

First, 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 today. Lower sea levels reduced pressure on the bedrock beneath Antarctic ice shelves, allowing the land underneath to slowly rise upward. That uplift helped support additional thickening of coastal ice.

Together, these mechanisms helped create the larger and more persistent Antarctic ice sheets that later defined Earth's ice age cycles.

"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.

What the Findings Could Mean for the Future

The study highlights that ice sheets may not always respond to climate change in a slow, predictable way. Instead, they can suddenly shift into a much more sensitive state after crossing critical climate thresholds.

Scientists say understanding these abrupt transitions is essential for improving future projections of Antarctic ice loss and global sea level rise.