The Digester

3-million-year-old Antarctic ice shows unexpectedly low Pliocene CO2 and methane

Mar 18th 2026

Air bubbles trapped in a 3-million-year-old Allan Hills ice core yield the first direct Pliocene gas measurements, showing CO2 at 250 ppm and methane at 507 ppb, far below earlier estimates and prompting calls for further validation and model testing.

  • Scientists measured 250 ppm CO2 and 507 ppb methane from 3-million-year-old ice at Allan Hills.
  • These direct measurements are much lower than prior indirect CO2 estimates of about 400 ppm and far below present levels.
  • The late Pliocene was roughly 1°C warmer than today with sea levels up to 25 meters higher, making it a key past climate analogue.
  • If confirmed, the low greenhouse gas values could imply the climate is more sensitive to small CO2 changes than currently thought.
  • Researchers and outside experts say the record needs validation and comparison with continuous cores like Beyond EPICA because the ancient ice may not represent a global or peak warm interval.

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