Numerical simulation study of temperature change over East China in the past millennium

Despite many studies on reconstructing the climate changes over the last millennium in China, the cause of the China's climate change remains unclear. We used the UVic Earth System Climate Model (UVic Model), an Earth system model of intermediate complexity, to investigate the contributions of climate forcings (e.g. solar insolation variability, anomalous volcanic aerosols, greenhouse gas, solar orbital change, land cover changes, and anthropogenic sulfate aerosols) to surface air temperature over East China in the past millennium. The simulation of the UVic Model could reproduce the three main characteristic periods (e.g. the Medieval Warm Period (MWP), the Little Ice Age (LIA), and the 20th Century Warming Period (20CWP)) of the northern hemisphere and East China, which were consistent with the corresponding reconstructed air temperatures at century scales. The simulation result reflected that the air temperature anomalies of East China were larger than those of the global air temperature during the MWP and the first half of 20CWP and were lower than those during the LIA. The surface air temperature of East China over the past millennium has been divided into three periods in the MWP, four in the LIA, and one in the 20CWP. The MWP of East China was caused primarily by solar insolation and secondarily by volcanic aerosols. The variation of the LIA was dominated by the individual sizes of the contribution of solar insolation variability, greenhouse gas, and volcano aerosols. Greenhouse gas and volcano aerosols were the main forcings of the third and fourth periods of the LIA, respectively. We examined the nonlinear responses among the natural and anthropogenic forcings in terms of surface air temperature over East China. The nonlinear responses between the solar orbit change and anomalous volcano aerosols and those between the greenhouse gases and land cover change (or anthropogenic sulfate aerosols) all contributed approximately 0.2A degrees C by the end of 20th century. However, the output of the energy-moisture balance atmospheric model from UVic showed no obvious nonlinear responses between anthropogenic and natural forcings. The nonlinear responses among all the climate forcings (both anthropogenic and natural forcings) contributed to a temperature increase of approximately 0.27A degrees C at the end of the 20th century, accounting for approximately half of the warming during this period; the remainder was due to the climate forcings themselves.