The Role of Clouds in Polar Amplification

Polar surface temperatures are expected to warm 2-3 times faster than the global mean surface temperature; a phenomenon referred to as polar amplification. Therefore, understanding individual process contributions to polar warming response is critical to understanding the overall climate response. The coupled feedback response analysis method (CFRAM) is applied to decompose the zonal mean, vertical temperature response within a transient 1% per year CO2 increase simulation of the NCAR CCSM4 into individual radiative and non radiative climate feedback process contributions. The surface albedo feedback provides the strongest contributions to polar amplification, +3-4 K. However, clouds and dynamic transport by the atmosphere and ocean are found to be important processes controlling the overall surface and atmospheric temperature response. In terms of polar amplification, atmospheric dynamic transport and the net cloud feedback contribute +0.5 K and up to +1.5 K to the polar surface temperature response, respectively, in both hemispheres. Ocean heat transport opposes contributions from atmospheric heat transport and cloud feedback and cools the polar surface temperatures due to enhanced heat transport to the deeper ocean. A comparison is made between NCAR CCSM4 and idealized GCM results to investigate the role of clouds on polar amplification. The comparison reveals a limited impact of control climate cloudiness on the polar surface temperature response. In the absence of clouds, the polar surface warming results from direct radiative perturbations as the surface, whereas in the presence of time mean clouds the polar surface warming is largely caused by enhanced downward radiation to the surface. Clouds are shown to exhibit a significant influence on the vertical distribution of the external forcing and water vapor feedback, which alters the atmospheric heat transport response.