Terrestrial nitrogen feedbacks may accelerate future climate change

The effects of nitrogen (N) constraints on future terrestrial carbon (C) dynamics are investigated using the O‐CN land surface model. The model's responses to elevated [CO 2 ] and soil warming agree well with observations made in ecosystem manipulation studies. N dynamics reduce terrestrial C storage due to CO 2 fertilization over the period 1860–2100 by ∼50% (342 Pg C) mainly in mid‐high latitude ecosystems, compared to a simulation not accounting for N dynamics. Conversely, N dynamics reduce projected losses of land C due to increasing temperature by 16% (49 Pg C); however, this effect is prevalent only in mid‐high latitude ecosystems. Despite synergistic interactions, the balance of these opposing effects is a significant reduction in future net land C storage. Terrestrial N dynamics thereby consistently increase atmospheric [CO 2 ] in the year 2100 with a median value of 48 (41–55) ppmv, corresponding to an additional radiative forcing of 0.29 (0.28–0.34) W m −2 .