Ice Core Studies Reveal 3 Million Years of Climate Data

New analyses of ancient ice from Antarctica provide insights into Earth's climate history.

Mar. 19, 2026 at 3:02am

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New research analyzing ancient ice from Antarctica has extended the history of Earth's climate records, revealing details about how the planet's climate has changed over the last 3 million years. The findings, published in two papers in the journal Nature, show that while Earth's climate has cooled significantly during this period, the decline in heat-trapping greenhouse gases like carbon dioxide and methane has been relatively modest.

Why it matters

This research provides a much longer-term perspective on Earth's climate history, going back millions of years further than previous studies. It suggests that factors beyond just greenhouse gas levels, such as changes in Earth's reflectivity, vegetation, ice cover, and ocean circulation, have played important roles in the planet's long-term cooling over the past 3 million years.

The details

The studies, led by researchers at Oregon State University's COLDEX program, used air trapped in ancient ice from Antarctica's Allan Hills region to analyze changes in ocean temperatures and greenhouse gas levels. They found that average ocean temperatures have declined by 2-2.5°C over the past 3 million years, with much of that cooling happening early on as ice sheets formed in the Northern Hemisphere. In contrast, atmospheric carbon dioxide levels only declined modestly, from around 250 ppm 2.7 million years ago to about 230 ppm 1 million years ago. Methane levels remained relatively stable at around 500 ppb over the same period.

  • The research analyzed ice core samples dating back 3 million years.
  • Carbon dioxide levels were around 250 ppm 2.7 million years ago and declined to about 230 ppm 1 million years ago.
  • Methane levels remained relatively stable at around 500 ppb over the past 3 million years.

The players

Julia Marks-Peterson

A doctoral student at Oregon State University who led one of the studies.

Sarah Shackleton

A former postdoctoral fellow at Princeton University, now a professor at Woods Hole Oceanographic Institution, who led one of the studies.

Ed Brook

The director of the COLDEX program at Oregon State University, a paleoclimatologist who co-authored the studies.

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What they’re saying

“Those snapshots extend climate records from ice much further than previously possible. These longer records are also now raising new questions about Earth's climate evolution and how far back in time we might be able to go with ice core data.”

— Ed Brook, Director of the COLDEX program at Oregon State University

“The noble gases in ice provide a unique way to look at ocean temperature change. Other methods can give you information about ocean temperature at a single site, but this gives a more global view.”

— Sarah Shackleton, Professor at Woods Hole Oceanographic Institution

“Our hope is that this work will refine our view of past warmer climates and sharpen our understanding of how different elements of the Earth system interact.”

— Julia Marks-Peterson, Doctoral student at Oregon State University

What’s next

COLDEX researchers recently discovered ice as old as 6 million years at the bottom of one of their cores and are currently developing new data from these older samples. Recently completed drilling of new ice cores should access additional old ice. Researchers are also investigating methods to test carbon dioxide reconstruction, studying other gases in the ice cores and developing a deeper understanding of the conditions that lead to preservation of very old ice, which should help identify new targets for drilling.

The takeaway

This research provides a much longer-term perspective on Earth's climate history, revealing that the planet's cooling over the past 3 million years cannot be fully explained by just declining greenhouse gas levels. It suggests that a complex interplay of factors, including changes in Earth's reflectivity, vegetation, ice cover, and ocean circulation, have all contributed to the long-term climate trends observed in this study.