Projected changes in near-surface relative humidity (RH) remain highly model-dependent over land and may have been underestimated by the former generation global climate models. Here the focus in on the recent CNRM-CM6-1 model, which shows an enhanced land surface drying in response to quadrupled atmospheric CO₂ compared to its CNRM-CM5 predecessor. Atmosphere-only experiments with prescribed sea surface temperature (SST) are used to decompose the simulated RH changes into separate responses to uniform SST warming, pattern of SST anomalies, changes in sea-ice concentration, as well as direct radiative and physiological CO₂ effects. Results show that the strong drying simulated by CNRM-CM6-1 is due to both fast CO₂ effects and a SST-mediated response. The enhanced drying compared to CNRM-CM5 is partly due to the introduction of the physiological CO₂ effect that was not accounted for in CNRM-CM5. The global ocean warming also contributes to the RH decline over land, in reasonable agreement with the moisture advection mechanism proposed by earlier studies which however does not fully capture the contrasted RH response between the two CNRM models. The SST anomaly pattern is a significant driver of changes in RH humidity at the regional scale, which are partly explained by changes in atmospheric circulation. The improved land surface model may also contribute to a stronger soil moisture feedback in CNRM-CM6-1, which can amplify the surface aridity induced by global warming and, thereby, lead to a non-linear response of RH.

预计近地表相对湿度（RH）的变化在很大程度上取决于模型，并且可能被前几代全球气候模型低估了。这里重点关注最新的CNRM-CM6-1模型，该模型显示了与其CNRM-CM5的前身相比，对四倍的大气CO ₂响应，陆地表面干燥增强了。仅在规定的海面温度（SST）的大气实验中，将模拟的RH变化分解为对统一的SST变暖，SST异常的模式，海冰浓度的变化以及直接的辐射和生理CO ₂效应的单独响应。结果表明，CNRM-CM6-1模拟的强干燥是由于快速CO ₂效应和SST介导的反应。与CNRM-CM5相比，干燥增强了，部分原因是引入了生理CO ₂效应，而这在CNRM-CM5中没有考虑。全球海洋变暖也促使陆地上的相对湿度下降，这与早期研究提出的水分对流机制合理地吻合，但是该机制未能完全捕捉到两个CNRM模型之间相对的相对湿度响应。SST异常模式是区域尺度RH湿度变化的重要驱动力，这在一定程度上可以通过大气环流的变化来解释。改进的地表模型还可能有助于CNRM-CM6-1中更强的土壤水分反馈，从而可以放大由于全球变暖引起的地表干旱，从而导致RH的非线性响应。