Diagnosis of the weakened global land carbon sink enhancement in recent decades: When and where the shifts occurred.

The terrestrial carbon sink is a major regulator of atmospheric carbon dioxide (CO2) growth, yet its long-term trajectory and stability remain uncertain. Linear trend-based assessments may obscure nonlinear evolution and trend shifts. Here, we reassess global terrestrial carbon sink dynamics from 1981 to 2020 using ensemble outputs from dynamic global vegetation models combined with ensemble empirical mode decomposition. We find that although the global land carbon sink has approximately doubled, its rate of enhancement has declined sharply, falling to nearly half of its early-period value. This slowdown is spatially heterogeneous, with widespread stagnation or reversals across equatorial and northern temperate regions, slower growth in boreal and southern temperate zones, and sustained increases mainly limited to the northern equatorial region. The fraction of land exhibiting positive trends has declined since the late 1990s, a signal largely masked by linear analyses. Dominance of interannual variability indicates low temporal stability, challenging linear, magnitude-based assessments of land-based climate mitigation potential.