Marks-Peterson, J., Shackleton, S., Higgins, J. et al.
Nature (2026)doi: 10.1038/s41586-025-10032-y
The evolution of greenhouse gases in Earth’s atmosphere over the last 3 million years is uncertain beyond the continuous ice core record (800,000 years). Here we present new measurements of carbon dioxide (CO2) and methane (CH4) for the period between 3.1 and 0.4 million years ago (Ma) from shallow ice cores drilled in the Allan Hills Blue Ice Area (BIA), Antarctica. The records are complicated by postdepositional processes (folding, thinning, recrystallization, and respiration) and likely represent averages over glacial cycles weighted by climate-dependent differences in accumulation rates. Assuming this weighting is constant, our values permit direct reconstructions of atmospheric greenhouse gases (CO2 and CH4). Across the Pleistocene, we find no significant change in mean CH4 and a small decline of ~20 ppm in CO2 between 2.9 and 1.2 Ma, followed by stable concentrations (+/- 10 ppm) across the MPT. Results for samples aged 2.8 to 3.1 Ma affected by respiration and corrected using stable carbon isotopes in CO2 (δ13C) yield mean atmospheric CO2 levels that are indistinguishable from the Early Pleistocene (250 +/- 10 ppm). Although paleoclimate archives from Antarctic Blue Ice Areas are complex, our new records show that measurements of greenhouse gases in ice cores can be extended to the Late Pliocene, providing snapshots of Earth’s climate system over a time of global cooling and falling sea level.
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