A PNAS study reports that ice cores recovered from Allan Hills, East Antarctica, extend the direct climate record to about 6 million years — roughly five times farther than previous records. The shallow but ancient cores preserve trapped air and chemical signals used to reconstruct past temperatures and atmospheric composition. The samples suggest this region was roughly 12°C (22°F) warmer six million years ago, underscoring the value of paleoclimate data for understanding long-term climate variability and informing responses to rapid modern warming.
Antarctic Ice Cores Extend Climate Record to 6 Million Years — Reveal a Much Warmer Past
A PNAS study reports that ice cores recovered from Allan Hills, East Antarctica, extend the direct climate record to about 6 million years — roughly five times farther than previous records. The shallow but ancient cores preserve trapped air and chemical signals used to reconstruct past temperatures and atmospheric composition. The samples suggest this region was roughly 12°C (22°F) warmer six million years ago, underscoring the value of paleoclimate data for understanding long-term climate variability and informing responses to rapid modern warming.
10:59 AM, 11/16/2025Science
Antarctic ice cores push climate record back to ~6 million years
A new study in the Proceedings of the National Academy of Sciences reports that ice from the Allan Hills region of East Antarctica preserves a direct climate record stretching back about 6 million years — roughly five times farther than the previous record. The work, summarized by Oregon State University, is part of the Center for Oldest Ice Exploration (COLDEX), a collaboration of 15 research institutions.
The field team, led by Sarah Shackleton of the Woods Hole Oceanographic Institution and John Higgins of Princeton University, recovered shallow but exceptionally old ice cores in a remote part of Allan Hills. COLDEX Director Ed Brook said the group had hoped to recover ice up to about three million years old, making this result a substantial and unexpected advance.
‘Ice cores are like time machines,’ Shackleton said, noting the Allan Hills samples let scientists peer much further back in Earth’s history than previously possible.
Antarctic ice cores preserve more than frozen water: they contain tiny trapped air bubbles and chemical signatures that record atmospheric composition and temperature at the time each layer formed. By extracting gases and measuring stable isotopes and other tracers, scientists can date layers and reconstruct past climates.
The Allan Hills cores indicate that this part of Antarctica was roughly 12°C (about 22°F) warmer about six million years ago. For context, the U.S. National Oceanic and Atmospheric Administration (NOAA) estimates the global average temperature has risen by about 2°F over the last 175 years. Researchers emphasize that these long-term paleoclimate data are essential for distinguishing natural variability from modern, human-driven change.
Local conditions that helped preserve such ancient ice near the surface likely include a combination of topography, persistently strong winds that scour fresh snowfall, and extremely low temperatures that slow ice flow. Those factors make Allan Hills one of the rare places on Earth where very old ice can be recovered from relatively shallow depths, though the site is challenging for field teams.
While the new record reveals that Antarctica has undergone much warmer periods in the deep past, scientists caution against simplistic comparisons. The paleoclimate record shows how Earth's climate system responds to long-term forcings; the rapidity and scale of recent warming, driven by emissions of greenhouse gases, are what raise concern for modern societies — contributing to polar ice loss, sea level rise and increased extreme weather risks.
Why this matters: Building a robust, well-dated library of ice cores is critical for testing climate models, improving projections of future change, and informing policy decisions. The Allan Hills discovery supplies concrete, ancient data that will help researchers better understand past climate states and refine our view of modern warming.