Contributions of Natural and Anthropogenic Forcing Factors to Twentieth‐Century Temperature Change: Results from the Simulation of LASG/IAP Climate System Model FGOALS_gl

Abstract

AbstractContributions of natural and anthropogenic forcing factors to the temperature change in the twentieth‐century are evaluated with a climate system model named FGOALS_gl, which was developed by LASG/IAP. Two sets of numerical experiments were done. The first is an all‐forcing in which both the natural forcing agents and the anthropogenic forcing agents were specified, the other is a natural‐only forcing run in which only the natural forcing agents were specified. The HadCRUT3v dataset is used to validate the model. Observed warming trends on a global scale and in many regions are simulated more realistically in the all‐forcing run than in the natural‐only forcing experiment. The simulations support the idea that the twentieth‐century global warming was resulted from a combination of the natural and anthropogenic forcing factors, with the latter being the dominant cause of the pronounced late twentieth‐century warming. For global and hemispheric mean temperatures, the external forcing factors explain most of the variance. However, internal variability is dominant over the tropical eastern Pacific and the North Atlantic. Attribution generally becomes more difficult on regional scales due to both a decreasing externally forced signal level and an increasing internally generated noise level. The reproducibility of the surface air temperature averaged over China is lower than that of the global and hemispheric mean. The model results suggest that anthropogenic forcing factors may have played a dominant role in the late twentieth century warming over China.