Overview
- Two Nature studies analyzed disrupted Allan Hills blue‑ice samples to reconstruct past mean ocean temperature and atmospheric gases using noble‑gas ratios and trapped air.
- Noble‑gas proxies indicate the global ocean cooled by about 2 to 2.5 Celsius degrees since the Pliocene, with deep‑ocean cooling occurring earlier than surface cooling.
- Direct measurements from ancient bubbles show carbon dioxide near 250 ppm around 2.7 million years ago, declining by roughly 20 ppm by 1 million years ago, and methane near 500 ppb with little long‑term change.
- The results imply that major climate transitions likely involved shifts in ocean circulation and other Earth‑system factors beyond greenhouse gases alone.
- Researchers stress that the Allan Hills record is non‑chronological and probably averages multiple cycles, so comparisons with continuous cores such as Beyond EPICA and further sampling will be used to test and refine these findings.