The intensification of soil extreme heat further accelerates the rise of atmospheric extreme temperature over China

Soil temperature is recognized as a fundamental factor influencing the intensity and frequency of heatwaves. However, the degree to which soil temperature regulates the release of organic carbon through soil respiration and its contribution to atmospheric warming still needs to be clarified. Through site and reanalysis data, the trend of soil extreme high heat intensity index exceeded that of air in about 75% of regions in China from 1961 to 2023. For extreme high heat frequency and duration, this proportion is even greater, reaching 78% and 88% respectively. Particularly in Northeast China, the increasing trend for soil extreme heat is nearly double that of air. In this context, the intensified soil extreme heat is markedly accelerating soil respiration rates, with a remarkable increase of 33.6% reported in North China. This further enhances carbon dioxide (CO 2 ) release, with forest and agricultural ecosystems identified as significant contributors to carbon emissions in Northeast China. Furthermore, the impact of rising soil extreme heat on air temperatures is projected to intensify in the future, especially in North China, which is expected to increase by 30% as the global temperature escalating from 1.5 to 2.0°C. Future increases in soil extreme heat intensity could further enhance soil respiration, exacerbating CO 2 emissions and accelerating future warming.