Climate Sensitivity and Feedback of a New Coupled Model (K-ACE) to Idealized CO2 Forcing

Abstract

Climate sensitivity and feedback processes are important for understanding Earth’s system response to increased CO2 concentration in the atmosphere. Many modelling groups that contribute to Coupled Model Intercomparison Project phase 6 (CMIP6) have reported a larger equilibrium climate sensitivity (ECS) with their models compared to CMIP5 models. This consistent result is also found in the Korea Meteorological Administration Advanced Community Earth System model (K-ACE). Idealized climate simulation is conducted as an entry card for CMIP6 to understand Earth’s system response in new coupled models and compared to CMIP5 models. The ECS in the K-ACE is 4.83 K, which is higher than the range (2.1–4.7 K) of CMIP5 models in sensitivity to CO2 change and higher bound (1.8–5.6 K) of CMIP6 models. The radiative feedback consists of clear-sky and cloud radiative feedback. Clear-sky feedback of K-ACE is similar to CMIP5 models whereas cloud feedback of K-ACE is more positive. The result is attributable for strong positive shortwave cloud radiative effect (CRE) feedback associated with reduced low-level cloud cover at mid latitude in both hemispheres. Despite the cancellations in strong negative long wave CRE feedback with the changes in high-level clouds in the tropics, shortwave CRE has a dominant effect in net CRE. Detailed understanding of cloud feedback and cloud properties needs further study.

Sea Level Rise Drivers and Projections from Coupled Model Intercomparison Project Phase 6 (CMIP6) under the Paris Climate Targets: Global and around the Korea Peninsula

“…In addition, the simulated SLR around the Korean Peninsula (Figure 1b) by CMIP6 (128 mm) is larger than that by CMIP5 (76 mm; [3]). This appears to be related to high climate sensitivity, because the response to past global warming in the CMIP6 models tends to be large [50,51]. However, the simulated global SLR from the CMIP6 ensemble mean (Figure 1a) is similar to observations in recent periods (the PD period in this study), agreeing well with recent studies [3,52].…”