Soil organic carbon (SOC) changes under future climate warming are difficult to quantify in situ. Here we apply an innovative approach combining space-for-time substitution with meta-analysis to SOC measurements in 113,013 soil profiles across the globe to estimate the effect of future climate warming on steady-state SOC stocks. We find that SOC stock will reduce by 6.0 ± 1.6% (mean±95% confidence interval), 4.8 ± 2.3% and 1.3 ± 4.0% at 0–0.3, 0.3–1 and 1–2 m soil depths, respectively, under 1 °C air warming, with additional 4.2%, 2.2% and 1.4% losses per every additional 1 °C warming, respectively. The largest proportional SOC losses occur in boreal forests. Existing SOC level is the predominant determinant of the spatial variability of SOC changes with higher percentage losses in SOC-rich soils. Our work demonstrates that warming induces more proportional SOC losses in topsoil than in subsoil, particularly from high-latitudinal SOC-rich systems.

Soil organic carbon (SOC) mineralization is a key component of the global carbon cycle. Its temperature sensitivity Q ₁₀ (which is defined as the factor of change in mineralization with a 10 °C temperature increase) is crucial for understanding the carbon cycle-climate change feedback but remains uncertain. Here, we demonstrate the universal control of carbon quality-availability tradeoffs on Q ₁₀ . When carbon availability is not limited, Q ₁₀ is controlled by carbon quality; otherwise, substrate availability controls Q ₁₀ . A model driven by such quality-availability tradeoffs explains 97% of the spatiotemporal variability of Q ₁₀ in incubations of soils across the globe and predicts a global Q ₁₀ of 2.1 ± 0.4 (mean ± one SD) with higher Q ₁₀ in northern high-latitude regions. We further reveal that global Q ₁₀ is predominantly governed by the mineralization of high-quality carbon. The work provides a foundation for predicting SOC dynamics under climate and land use changes which may alter soil carbon quality and availability.