Warming‐Induced Shifts in Relative Humidity Reshape Global Soil Organic Carbon Storage

Soil organic carbon (SOC) underpins food production, ecosystem functioning, and climate regulation. Yet how global SOC storage will respond to future land‐use and climate change remains uncertain. Here we synthesized global datasets from the Food and Agriculture Organization of the United Nations, Land‐Use Harmonization, and World Bank describing SOC, land‐use (cropland, pasture, rangeland, and non‐forest and forest natural ecosystems), and climate (mean annual temperature, mean annual precipitation, maximum of daily max‐temperature, maximum of one‐day precipitation, maximum number of consecutive dry days, maximum number of consecutive wet days, and relative humidity). To assess the effects of land‐use and climate change on SOC, we developed a four‐dimensional deep learning model that incorporates spatial context, soil depthwise information (0–200 cm), and temporal iteration. The model reproduced global SOC patterns with high accuracy ( R 2 = 0.79–0.91). Our results show smaller SOC loss under lower climate forcing, reflecting the benefits of sustainable management and limited warming. Notably, we identified a previously overlooked global control on SOC—relative humidity (RH). Under future warming, widespread SOC losses emerged in regions experiencing declining relative humidity, especially in the tropical zone. Localized gains occurred in a few arid ecosystems where RH increased. The polar zone transitioned from gaining to losing SOC as intensified warming further reduced RH. Warming‐induced shifts in RH therefore reshape the global SOC landscape. Additionally, we found SOC changes attenuated with increasing soil depth in tropical, arid, and temperate zones but amplified in continental and polar regions. Together, these findings highlight the need for region‐specific SOC stewardship, including moisture‐conserving management in drying regions and protection of emerging carbon sinks in humidifying areas. Our study advances understanding of land‐climate‐soil interactions and establishes a new foundation for ecosystem assessment and sustainable management.