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Scientists analyzed air bubbles trapped in 3-million-year-old Antarctic ice and discovered that Earth cooled drastically while CO₂ and methane remained almost stable, revealing a new climate mystery.
An analysis of air bubbles trapped in approximately 3-million-year-old Antarctic ice revealed an unexpected result that is drawing the attention of climatologists: during a long period of global cooling on Earth, carbon dioxide and methane levels remained relatively stable. The discovery was reported in April 2026 by ScienceDaily based on studies published in the scientific journal Nature by researchers affiliated with Oregon State University and the international COLDEX project, specializing in ancient Antarctic ice.
Scientists analyzed samples collected in the Allan Hills region of East Antarctica, one of the few areas on the planet capable of preserving extremely ancient ice with intact atmospheric gases. Within this ice were tiny air bubbles that function as natural time capsules, preserving records of Earth’s atmosphere from millions of years ago. What the researchers found surprised the scientific community.
Even with a strong cooling of the oceans over the past 3 million years, greenhouse gas levels changed much less than climate models expected. The discovery suggests that factors such as ocean circulation, the expansion of ice sheets, and the planet’s reflectivity may have played a much larger role in regulating Earth’s ancient climate than previously thought.
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Antarctic ice functions as a natural climate archive
When snow falls on Antarctica, small amounts of air become trapped between ice crystals. Over thousands and millions of years, these bubbles preserve actual samples of Earth’s atmosphere from that period. This allows scientists to directly analyze the concentration of carbon dioxide, methane levels, the chemical composition of the atmosphere, and the temperature of ancient oceans.
The samples used in the study came from Allan Hills, a region known as a “blue ice” area, where natural glacier movements bring extremely ancient ice closer to the surface.
The planet cooled much more than CO₂ indicated
One of the studies analyzed noble gases present in the air bubbles to reconstruct the average ocean temperature. The results indicated that the planet’s oceans cooled by about 2 °C to 2.5 °C over the past 3 million years.
This cooling process coincided with the expansion of large ice sheets in the Northern Hemisphere, a period that profoundly transformed the global climate. The problem is that the greenhouse gases found in the samples did not keep pace with this change to the same extent.
Carbon dioxide levels generally remained below 300 parts per million and varied relatively little over the analyzed period. Methane also showed changes considered modest by the researchers. It was precisely this incompatibility that drew attention.
Earth’s ancient climate may have been controlled by more complex forces
Scientists do not claim that CO₂ ceased to be important for Earth’s climate. What the study suggests is something more complex: other climatic mechanisms may have played a much larger role during certain geological periods. Among the main factors pointed out by the researchers are:
- Changes in ocean circulation;
- Expansion and retraction of large ice sheets;
- Changes in the planet’s albedo;
- Reorganization of vegetation cover.
Albedo is Earth’s ability to reflect sunlight. Ice-covered surfaces reflect much more energy back into space than dark oceans or forests, for example. This means that the growth of polar ice caps can generate an additional cooling effect capable of amplifying climate changes over thousands of years.
Oceans may have played a larger role than scientists imagined
The research also reinforces the importance of ocean currents in regulating the global climate. Oceans function as a gigantic system for redistributing heat around the planet. Changes in ocean circulation can profoundly alter heat transport between continents, polar ice formation, carbon absorption, and global climate patterns. According to the researchers, gradual alterations in these systems may have contributed to the global cooling observed in Antarctic records.
The study helps understand how Earth’s climate works at extreme scales
One of the most important parts of the discovery is that it expands scientific knowledge about very ancient climatic periods of Earth. Until today, most direct atmospheric records obtained from ice reached about 800,000 years.
The analyzed samples now push this window to approximately 3 million years. This allows comparing the current climate with ancient periods when Earth had different conditions than today. Researchers believe that understanding these periods can help improve climate models used to predict future changes.
A climatic mystery buried in ice for millions of years
The study shows that the Earth’s climate system may be even more complex than scientists imagined. For millions of years, oceans, ice, ocean currents, and the atmosphere seem to have interacted in ways that modern models are still trying to fully comprehend.
And all of this was preserved in tiny invisible air bubbles trapped within Antarctic ice. Now, these natural time capsules are helping scientists reconstruct chapters of Earth’s climate that remained hidden for millions of years beneath Antarctica.
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