Abstract: The external forcing and the internal variability in numerical simulations of last millennium climate by the community earth system model (CESM) are investigated by the spectral decomposition using wavelet. The simulations include five different ensembles of single forcing, greenhouse gas levels, volcanic variations, changes in land use/land cover, orbital variations, and total solar irradiance. And an ensemble of nine experiments of those single forcing combined (the full forcing) was also conducted. All the experiments have almost identical spectra in the high-frequency band. However, in each ensembles of different external forcing, the low-frequency spectra indicate significantly different spectral exponents in average, while the internal variability can be realized by the small variations around the average.
