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.

Global climate change is expected to increase the frequency of drought and heavy precipitation, which could create more frequent drying‐rewetting cycles (DWC) in the soils. Although the DWC effects on soil organic carbon (SOC) decomposition have been widely studied, the effect of DWC and the subsequent legacy effect on the decomposition of different SOC pools is still unclear. We conducted a 128‐d laboratory incubation to investigate the DWC effects by using soils from old‐field for 15 years (OF, representing active SOC), bare‐fallow (BF)for 15 years, and BF for 23 years plus an extra 815‐d incubation (BF+, representing relatively resistant SOC). The experiment included nine 10‐d DWC of three treatments: (1) one mean constant‐moisture at 60% water‐holding capacity (WHC), (2) a mild DWC with 10‐d drying to 40% WHC and immediately rewetting to 80% WHC, and (3) a strong DWC with 10‐d drying to 20% WHC and immediately rewetting to 100% WHC. Following the DWC period (0–90 d), there was a 10‐d stabilization period (adjusting all treatments to 60% WHC), and then a 28‐d extended incubation under the constant moisture of 60% WHC. During the DWC period, the strong DWC had a strong effect on CO2 release compared with the constant‐moisture control, reducing the SOC decomposition of OF by 8% and BF by 10%, while increasing the SOC decomposition of BF+ by 16%. In addition, during the extended period, both mild and strong DWC significantly increased SOC mineralization of OF, but decreased that of BF and BF+. This legacy effect induced by DWC compensated for the changes in CO2 release during the DWC period, resulting in the minor response of SOC decomposition of OF and BF+ to the DWC during the entire incubation. Together, DWC could create both direct and legacy effects, and these effects vary with DWC intensity and SOC pools.