Researchers extracted ice cores from Antarctica dating back 3 million years to analyze ancient atmospheric compositions. By measuring trapped air bubbles, scientists found that CO2 concentrations around 400 ppm during the Pliocene epoch led to significantly higher global temperatures and sea levels. This data provides a natural analogue for modern climate change, helping scientists calibrate computer models and determine climate sensitivity. The findings reinforce the direct correlation between greenhouse gas concentrations and the melting of polar ice sheets.
