Assess advanced understanding of how global carbon budgets are estimated by comparing top‑down (atmospheric inversion, remote sensing) and bottom‑up (emission inventories, process models) methodologies and Earth system model projections; identify and evaluate major uncertainties (carbon cycle feedbacks, aerosols, non‑CO2 forcings, land‑use change, measurement and inventory errors, internal variability); and judge implications of differing budget estimates for the timing, feasibility, equity, and policy design of net‑zero targets.