What was done
Noting that "the Global Precipitation Climatology Project (GPCP) has produced merged satellite and in situ global precipitation estimates, with a record length now over 26 years beginning 1979 (Huffman et al., 1997; Adler et al., 2003)," the authors used empirical orthogonal function (EOF) analysis to study annual GPCP-derived precipitation variations over the period of record.

What was learned
The first three EOFs accounted for 52% of the observed variance in the precipitation data. Mode 1 was associated with mature ENSO conditions and correlated strongly with the Southern Oscillation Index, while Mode 2 was associated with the strong warm ENSO episodes of 1982/83 and 1997/98. Mode 3, on the other hand, was uncorrelated with ENSO but was associated with tropical trend-like changes that were correlated with interdecadal warming of tropical sea surface temperatures. Globally, however, Smith et al. report that "the mode 3 variations average to near zero, so this mode does not represent any net change in the amount of precipitation over the analysis period."

What it means
Citing several climate modeling studies, Huntington (2006) states there is a "theoretical expectation" that global warming will result in significant increases in global precipitation. However, as a result of their analysis of global precipitation data over the period 1979-2004 (when climate alarmists claim the world warmed at a rate and to a degree that was unprecedented over the past two millennia), Smith et al. report that most of the precipitation variations in their global data set "are associated with ENSO and have no trend." As for the variations that are not associated with ENSO and that do exhibit trends, they say that the trends are associated "with increased tropical precipitation over the Pacific and Indian Oceans associated with local warming of the sea." However, they note that this increased precipitation "is balanced by decreased precipitation in other regions," so that "the global average change is near zero." Over the earth as a whole, therefore, one of the major "theoretical expectations" of the climate modeling community remains unfulfilled, even under the supposedly highly favorable thermal conditions of the last quarter century, which observation suggests that their other major "theoretical expectation," i.e., catastrophic CO2-induced global warming, may well remain unfulfilled too.

References
Adler, R.F., Susskind, J., Huffman, G.J., Bolvin, D., Nelkin, E., Chang, A., Ferraro, R., Gruber, A., Xie, P.-P., Janowiak, J., Rudolf, B., Schneider, U., Curtis, S. and Arkin, P. 2003. The version-2 global precipitation climatology project (GPCP) monthly precipitation analysis (1979-present). Journal of Hydrometeorology 4: 1147-1167.

Huffman, G.J., Adler, R.F., Chang, A., Ferraro, R., Gruber, A., McNab, A., Rudolf, B. and Schneider, U. 1997. The Global Precipitation Climatology Project (GPCP) combined data set. Bulletin of the American Meteorological Society 78: 5-20.

Huntington, T.G. 2006. Evidence for intensification of the global water cycle: Review and synthesis. Journal of Hydrology 319: 83-95.