We use existing palaeoclimate data and a statistical model to predict atmospheric CO₂ concentrations across the Mid-Pleistocene Transition. Our prediction assumes that the relationship between CO₂ and benthic ẟ¹⁸O_calcite over the past 800 000 years can be extended over the last 1.8 million years. We find no clear evidence from existing blue ice or proxy-based CO₂ data to reject the predicted record. A definitive test awaits analysis of continuous oldest ice core records from Antarctica.