Projections of future carbon storage by the land surface depend on three overarching factors: 1) how plant biomass and soil carbon respond to climate changes, 2) how plants respond to CO₂ enrichment, and 3) how effectively plants can move in response to shifting climate patterns. The implications of CO₂ enrichment on global carbon storage in vegetation and soil remain ambiguous despite nearly two decades of plot-level manipulative field experiments. Nevertheless, biogeochemical models often assume substantial plant fertilization in response to higher CO₂ concentrations. Here I demonstrate that simulated climate changes associated with the A1FI greenhouse gas emission scenario could trigger further losses of carbon from the land surface that exceed the amount of carbon currently contained in the atmosphere. Furthermore, model results suggest that plausible constraints on plant migration could cause an additional carbon loss from the land surface in excess of cumulative historical anthropogenic emissions. Taken together, this release of carbon from the land surface is sufficient to push atmospheric concentrations to levels found in the highest IPCC emission scenario (A1FI) even if anthropogenic emissions correspond to the lowest emission levels (B1).