Low CO₂ levels of the entire Pleistocene epoch

Quantifying ancient atmospheric pCO₂ provides valuable insights into the interplay between greenhouse gases and global climate. Beyond the 800-ky history uncovered by ice cores, discrepancies in both the trend and magnitude of pCO₂ changes remain among different proxy-derived results. The traditional paleosol pCO₂ paleobarometer suffers from largely unconstrained soil-respired CO₂ concentration (S(z)). Using finely disseminated carbonates precipitated in paleosols from the Chinese Loess Plateau, here we identified that their S(z) can be quantitatively constrained by soil magnetic susceptibility. Based on this approach, we reconstructed pCO₂ during 2.6-0.9 Ma, which documents overall low pCO₂ levels (<300 ppm) comparable with ice core records, indicating that the Earth system has operated under late Pleistocene pCO₂ levels for an extended period. The pCO₂ levels do not show statistically significant differences across the mid-Pleistocene Transition (ca. 1.2-0.8 Ma), suggesting that CO₂ is probably not the driver of this important climate change event.