Stratospheric water vapour (SWV), as a greenhouse gas, modulates the radiative energy budget of the climate system. It is sensitive to, and plays a significant role in the climate change. In this study, we investigate the SWV response to CO₂ increase with the Whole Atmosphere Community Climate Model (WACCM). In addition, we study its possible feedback on stratospheric temperature and relevant mechanisms. In our model experiments, the CO₂ concentration and sea surface temperature (SSTs) are changed at the same time, as well as separately, to enable separating the radiative-photochemical and dynamical response to CO₂ doubling scenarios. The model results show that the response of SWV to CO₂ doubling is dominated by the changes in the SSTs, with an increase of the SWV concentration by ~ 6 to 10% in most of the stratosphere and more than 10% in the lower stratosphere, except for winter pole in the lower stratosphere, where the CO₂ doubling decreases water vapour. The increase of SWV is mostly due to a dynamical response to the warm SSTs. Doubled CO₂ induces warm SSTs globally and further leads to moist troposphere and a warmer tropical and subtropical tropopause, resulting in more water vapour entering stratosphere from below. As a greenhouse gas, large increase of SWV in the lower stratosphere, in turn, affects the stratospheric temperature, resulting in a warming of the tropical and subtropical lower stratosphere, offsetting the cooling caused by CO₂ doubling.

平流层水蒸气（SWV）作为一种温室气体，调节了气候系统的辐射能收支。它对气候变化敏感，并在气候变化中起重要作用。在这项研究中，我们调查了SWV对整个大气社区气候模型（WACCM）对CO ₂增加的响应。此外，我们研究了其对平流层温度的可能反馈及其相关机制。在我们的模型实验中，同时以及分别更改了CO ₂浓度和海面温度（SST），以实现对CO ₂倍增方案的辐射光化学和动力学响应的分离。模型结果表明SWV对CO ₂的响应SST的变化决定了倍增，在平流层的大部分地区，SWV浓度增加了约6％至10％，在平流层的下部，SWV浓度增加了10％以上，但平流层下层的冬季极点除外₂倍减少水蒸气。SWV的增加主要归因于对温暖的SST的动力响应。CO ₂倍增会在全球范围内引发温暖的SST，并进一步导致对流层潮湿以及热带和亚热带对流层顶变暖，从而导致更多的水蒸气从下方进入平流层。作为温室气体，平流层下部的SWV的大量增加反过来又影响了平流层温度，导致热带和亚热带平流层的变暖，抵消了由CO ₂引起的冷却 加倍。