The dynamics of atmospheric CO₂ concentrations during and following the last deglaciation have mainly been ascribed to carbon release from and uptake in oceans, primarily in the Southern Ocean. But recent studies also point toward a terrestrial influence. We quantify dynamic changes to northern terrestrial carbon stocks from the Last Glacial Maximum (21,000 years) until present at millennial time steps using a combination of paleo-data and climate-biome modeling. During the deglaciation, northern land carbon storage declined by >300 petagrams of carbon with a minimum around 11,000 years, followed by progressively higher land carbon stocks during the Holocene. We find evidence that dynamic changes in terrestrial land carbon stocks were of a scale to exert large influence on atmospheric CO₂ concentrations and that postglacial terrestrial carbon stock dynamics were dominated by losses from permafrost-affected loess and gains into peatlands.