Barnett,T. P., 1999:
Comparison of near-surface air temperature variability in 11 coupled  global climate models
Journal of Climate, 12, 511-518.


The common variance between 100-yr-long control runs from 11 coupled global climate models (CGCMS) has been studied by use of common empirical orthogonal functions (EOFs). The results suggest that there is a considerable disparity between the CGCMs estimates of internal variability. About one-half of this difference can be attributed to model drift or other low-frequency variations in several of the models. However, even after accounting for this effect, it was found that the models can easily differ by a factor of 2 or more for the energy levels in different EOF mode (wave) numbers. Comparison with observations showed that no one model consistently reproduced the observed partial eigenvalue spectrum. Again, differences between observed and model energy levels were commonly a factor of 2 or more. It is speculated that at least some of the disagreement is due to the relative coarse resolution of the models used in this study. Separate analysis of a 1000-yr control run of the Geophysical Fluid Dynamics Laboratory model suggested that intramodel variability is much smaller than intermodel variability. It was also found that an estimate of the anthropogenic signal due to greenhouse gases and aerosols from the Max Planck Institute had strong spatial similarities to the leading modes of the models' common EOFs. This fact complicates the detection attribution problem.