Extreme Climate as the Primary Control of Global Soil Organic Carbon Across Spatial Scales

Soil organic carbon (SOC) stock exhibits substantial variability across spatial scales and depths. Drivers of such variability may be scale- and depth-dependent, but have been rarely systematically investigated. Assessing SOC measurements of 113,013 soil profiles worldwide, we show that climate, encompassing mean modern- and paleo-climate and climate extremes, is the predominant determinant across scales (from 50 km to the globe) and depths, explaining 34%–62% of the spatial variability of SOC stocks depending on the spatial scale and soil depth layer assessed. On finer scales (50–100 km), soil properties and mean modern- and paleo-climate are dominant in all soil depth layers. At broader scales (>100 km), the significance of climate extremes intensifies, alone explaining 27%–32% of the spatial variability of SOC stocks. Furthermore, we find nonlinear relationships of SOC stocks with most factors, while the relationship with the same factor is distinct across scales and depths. These results reinforce climate, particularly extremes, as the primary driving force of whole-soil carbon distribution across the globe, emphasizing the need to factor extremes into carbon management strategies.