What was done
The authors compared 79 coupled ocean-atmosphere climate simulations derived from twelve different state-of-the-art (as of the IPCC's Third Assessment Report) climate models forced by six different IPCC emission scenarios with observational data in order to evaluate how well they reproduce the spatio-temporal characteristics of the El Niņo-Southern Oscillation (ENSO) over the 20th century, after which they compare the various models' 21st-century simulations of ENSO and the Indian and West African monsoons among themselves.

What was learned
With respect to the past (20th century), Paeth et al. report that "all considered climate models draw a reasonable picture of the key features of ENSO." With respect to the future (21st century), on the other hand, they say that "the differences between the models are stronger than between the emission scenarios," while "the atmospheric component of ENSO and the West African monsoon are barely affected."

What it means
Quoting the researchers who performed the work, "the overall conclusion is that we still cannot say much about the future behavior of tropical climate." Hence, they say they consider their study to be "a benchmark for further investigations with more recent models in order to document a gain in knowledge or a stagnation over the past five years." We thus must await a similar analysis to be performed with what Paeth et al. call "the meanwhile available Fourth Assessment Report model data base," in order to see if the modelers have learned anything at all over the past five years, as a five-year period of "stagnation" in the gaining of knowledge is implied by them to be a very real possibility.