| Soils store a vast amount of carbon (C) and can potentially offset or exacerbate the climate change triggered by anthropogenic C emissions. Given the size of the soil C pool and its potentially substantial role in climate-carbon feedbacks, it is important to evaluate the magnitudes and spatial variability of near-future changes in soil C stocks. Such evaluation is typically done using process-based simulation models, but they often generate biased SOC stocks. Recent increase in diversity of observational data products facilitates development of new benchmarks, which can be used to improve the performance of the process-based simulation models. Moreover, diverse observational data products facilitate direct assessment of the near-future trajectories in soil C stocks. In this study I show that the observational data products for soil C ages, stocks, and heterotrophic respiration impose constraints on (1) the fractions of fresh C allocated to faster-decomposing C pool; (2) decay rates of labile and recalcitrant C; and, combined with satellite data on productivity, (3) near-future soil C trajectories. Maximum likelihood changes in soil C over a 10-year period amounted to a 27.2 Pg C loss, however the changes in soil C were highly uncertain, ranging from a 95.6 Pg C loss to a 32.3 Pg C gain. The biggest decadal C loss is projected to occur in croplands (4.94 Pg C), and the smallest - in temperate forests (0.34 Pg C). |