Last Millennial Climate Simulation of FGOALS

Abstract

Variations in surface air temperature (SAT) and the East Asian Summer Monsoon (EASM) during the last millennium have been simulated using the climate system model FGOALS-gl. This model is driven by both natural (solar irradiance, volcanic eruptions) and anthropogenic (greenhouse gases, sulfate aerosols) forcing agents. The major features of the simulated past millennial global mean SAT variations (including the Medieval Climate Anomaly (MCA), the Little Ice Age (LIA), and twentieth-century warming (20CW)) are generally consistent with those of climate reconstructions. In the simulation, solar and volcanic factors are the primary external forcing mechanisms of the climate system during the MCA and LIA, whereas the 20CW can be attributed primarily to increasing concentrations of greenhouse gases. The simulated MCA exhibits a cooling pattern over most parts of the globe with respect to the 1961-1990 mean conditions, which means that the 20CW (i.e., over the last millennium) is unprecedented in the simulation. Moreover, the LIA is characterized by pronounced coldness over the extra tropical NH continents. The simulated global mean SAT difference between MCA and LIA is 0.14 °C, with enhanced warming occurring over North America, the high-latitude North Atlantic, and the Eurasian continent. The centennial EASM variations exhibit a stronger EASM circulation for the MCA-LIA difference. The corresponding rainfall anomalies indicate excessive (deficient) rainfall in the north (south), and the stronger monsoon circulation is driven by an enhanced land-sea thermal contrast.