Century-scale changes of atmospheric CO2 during the last interglacial

The crucial role of atmospheric CO₂ in glacial-interglacial transitions is demonstrated by recent ice-core studies that highlight the importance of accurate CO₂ records for our understanding of Quaternary climate dynamics. Previous estimates of CO₂ levels during the last interglacial stage (the Eemian) relied on measurements on air trapped in the Antarctic Vostok ice core. Due to uncertainties associated with in situ chemical alteration and gas diffusion, there is a need for independent estimates of past CO₂ levels. Here we report 33 Eemian CO₂ estimates based on the stomatal index of Salix herbacea L. leaves preserved in Greenland sediments. We reconstruct Eemian CO₂ levels centered on 250–280 parts per million by volume (ppmv), in general agreement with ice- core data. Two deviating (lower) stomatal estimates may reflect diffusional smoothing of Vostok CO₂ data and indicate century- scale Eemian CO₂ variability.