Quantifying climate feedbacks in the middle atmosphere using WACCM

• Main Authors: Kuilman, Maartje Sanne, Zhang, Qiong, Cai, Ming, Wen, Qin
• Format: Text
• Language: English
• Published: 2020
• Subjects: Sea ice
• Online Access: https://doi.org/10.5194/acp-2019-1169; https://www.atmos-chem-phys-discuss.net/acp-2019-1169/

The importance of feedback processes in the middle atmosphere for surface and tropospheric climate is increasingly realized. To better understand feedback processes in response to a doubling of CO 2 we use the climate feedback response analysis method (CFRAM). We examine the middle atmosphere response to CO 2 doubling with respect to the pre-industrial state in the Whole Atmosphere Community Climate Model (WACCM). Globally, the simulated temperature decrease between 200 and 0.01 hPa (~ 12–80 km) is found to be −5.2 K in July and −5.5 K in January in WACCM. The CFRAM calculations show that the direct forcing of CO 2 alone would lead to an even stronger cooling of approximately 9 K in the middle atmosphere in both July and January. This cooling is being mitigated by the combined effect of the different feedback processes. The contribution from the ozone feedback causes a warming of approximately 1.5 K, mitigating the cooling due to changes in CO 2 . Changes in CO 2 also lead to changes in the middle atmosphere dynamics. The changes in dynamics play a large role locally, especially above 0.1 hPa. Other feedback processes, which are known to be important in the tropospheric and surface climate, such as the water vapor, albedo and cloud feedbacks are of minor importance in the middle atmosphere,although some effects are seen in the stratosphere, mainly through the responses to sea surface temperature and sea ice changes. It should be noted that there is a relatively large error term associated with the current method in the middle atmosphere, which can be explained by the linearization in the method.