Source or Sink? Precipitation Shapes Future Terrestrial Carbon Uptake in Australia

Nature‐based CO 2 removal must deliver sequestration beyond background terrestrial uptake and be resilient to future climate change. Regional‐scale simulations of future terrestrial carbon cycles are needed to establish baselines, map spatial variation in carbon uptake, and guide placement of nature‐based carbon removal projects. Using Australia as a case study, spanning biomes from tropical to semi‐arid, we simulated Australia’s future terrestrial carbon cycle (2015–2100) using a land‐surface model under low (SSP1‐2.6) and high (SSP3‐7.0) emissions scenarios (14 simulations). Simulations indicate that Australia is likely to remain a carbon sink in this century although sink strength is uncertain and strongly linked to variability in precipitation projections. Under SSP3‐7.0, cumulative carbon uptake ranged from 2.0 to 14.2 Pg C with end‐of‐century sequestration rates between 0.01 and 0.22 Pg C yr −1 . Under SSP1‐2.6, uptake was lower, ranging from −0.7 to 12.2 Pg C with rates between −0.2 and 0.04 Pg C yr −1 . Precipitation was the strongest correlate with carbon uptake, whereas CO 2 played a secondary role. Few regions consistently increased uptake across all climate futures, whereas several “hotspots” of decline were identified in southeastern and southwestern Australia. Interannual variability in carbon uptake is projected to increase in the savanna and sparsely vegetated biomes. Our results highlight challenges in identifying regions for nature‐based carbon removal and indicate a weakening terrestrial carbon sink under emissions pathways aligned with Paris agreement goals. This study underscores the value of regional‐scale simulations for informing policies to enhance carbon sinks and the critical importance of precipitation projections to future carbon dynamics.