Last Millennium Climate Simulated by the ICM Climate Model

In this study, the last millennium transient simulation of Integrated Climate Model (ICM) climate model developed in Center for Monsoon System Research, Institute of Atmospheric Physics, Chinese Academy of Sciences is presented. The model was driven by up-to-date external forcings, and the simulation could reproduce many large-scale climate variations of surface temperature and atmospheric oscillation suggested by reconstructions. The centennial scale changes of global monsoon were further studied. Results indicate that the overall variations of temperature and atmospheric oscillation during the last millennium are reasonably reproduced by ICM. The northern hemisphere surface temperature is higher than average during 900-1200 but lower than average during 1500-1800. The simulated hemispheric scale surface temperature shows an unprecedented warming from the 1800s to present. The simulation didn't well reproduce the reconstructed Atlantic Multi-decadal Oscillation (AMO) and Pacific Decadal Oscillation (PDO). Over the past millennium, the simulated global monsoon shows significant centennial variations. The global monsoon strengthens during 850-1050, 1150-1200, and 1300-1420. Conversely, it weakens during 1210-1300 and 16000-1850. In the last century, the global monsoon index shows a prominent upward trend. During the Medieval Warm Period (MWP), precipitation increases in most parts of the global monsoon regions, but decreases within the Little Ice Age (LIA). The global monsoon strengthens markedly during the Present Warm Period (PWP), and the precipitation rate in the equatorial western Pacific Ocean increases by 1mm/d.