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How have ice cores helped scientists study ancient carbon dioxide concentrations?

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World map shaded to show annual carbon dioxide emissions by country in 2022, with China, the United States, and India highlighted as top emitters in dark red. A bar chart below lists the top ten emitting countries by million metric tons. — Greenhouse gas Map of annual carbon dioxide emissions by country in 2014.

Ice cores serve as vital archives for studying ancient atmospheric composition because they contain tiny air bubbles trapped within the ice as snow was compressed and recrystallized over millennia.1

By extracting and analyzing the gas trapped in these bubbles, scientists can directly measure historical concentrations of carbon dioxide and other greenhouse gases. These records have revealed that carbon dioxide levels were significantly lower during past glacial periods compared to interglacial periods, often falling below pre-industrial levels.123

This data provides critical evidence that greenhouse gas concentrations are closely linked to climate change cycles. The observed fluctuations suggest that changes in carbon dioxide levels acted as a feedback mechanism, reinforcing and amplifying the cooling or warming trends during transitions between glacial and interglacial regimes. By comparing these findings with other paleoclimatic data, such as oxygen isotope records from marine sediments, researchers can better understand the complex interactions within the Earth system that drive long-term climatic shifts.132