Background
Climate model simulations of CO2-induced global warming have long depicted strong concomitant increases in global monsoon precipitation (Zhao and Kellog, 1988; Meehl and Washington, 1993; Chakraborty and Lal, 1994; Wang, 1994; Whetton et al., 1993, 1994; Hirakuchi and Giorgi, 1995; Li et al., 1995; Suppiah, 1995; Hulme et al., 1998; Zwiers and Kharin, 1998; Ueda et al., 2006). Of far greater importance, however, is what actual observations reveal about the subject.

What was done
After defining "a global monsoon rain domain according to annual precipitation range, using simple objective criteria," the authors derived an ensemble (arithmetic) mean of annual global monsoon precipitation for the period 1948-2003, based on four sets of monthly rain-gauge data for a 0.5-degree latitude/longitude grid of the land surface of the globe, as compiled by four different climate diagnostic groups.

What was learned
Wang and Ding discovered "an overall weakening of the global land monsoon precipitation in the last 56 years, primarily due to weakening of the summer monsoon rainfall in the Northern Hemisphere." Since 1980, however, they note that "the oceanic monsoon precipitation shows an increasing trend," but that "the global land monsoon rainfall has seen no significant trend."

With respect to the total (monsoon plus non-monsoon) land-sea combination, the two researchers report that since 1979 "no trend was seen for the total global precipitation (Allen and Ingram, 2002)," based on the Global Precipitation Climatology Project's 2.5 by 2.5 degree grid of precipitation data, a finding that was recently replicated by Smith et al. (2006).

What it means
Contrary to a long history of climate model predictions, earth's monsoon precipitation did not materially increase in response to the global warming of the past half century, nor did the planet's total precipitation increase in response to the warming of the past quarter century, during which time climate alarmists typically claim the earth warmed at a rate and to a level that was unprecedented over the past two millennia. Clearly, there seems to be a major disconnect between the virtual world of climate models, where significant warmings bring significant increases in precipitation, and the real world, where actual observational data suggest that such is not the case.

References
Allen, M.R. and Ingram, W.J. 2002. Constraints on future changes in climate and the hydrologic cycle. Nature 419: 224-232.

Chakraborty, B. and Lal, M. 1994. Monsoon climate and its change in a doubled CO2 atmosphere simulated by CSIRO9 model. TAO 5: 515-536.

Hirakuchi, H. and Giorgi, F. 1995. Multiyear present-day and 2xCO2 simulations of monsoon climate over eastern Asia and Japan with a regional climate model nested in a general circulation model. Journal of Geophysical Research 100: 21,105-21,125.

Hulme, M., Osborn, T.J. and Johns, T.C. 1998. Precipitation sensitivity to global warming: Comparison of observations with HADCM2 simulations. Geophysical Research Letters 25: 3379-3382.

Li, X., Yang, S., Zhao, Z. and Ding, Y. 1995. The future climate change simulation in east Asia from CGCM experiments. Quarterly Journal of Applied Meteorology 6: 1-8.

Meehl, G.A. and Washington, W.M. 1993. South Asian summer monsoon variability in a model with doubled atmospheric carbon dioxide concentration. Science 260: 1101-1104.

Smith, T.M., Yin, X. and Gruber, A. 2006. Variations in annual global precipitation (1979-2004), based on the Global Precipitation Climatology Project 2.5° analysis. Geophysical Research Letters 33: 10.1029/2005GL025393.

Suppiah, R. 1995. The Australian summer monsoon: CSIRO9 GCM simulations for 1xCO2 and 2xCO2 conditions. Global and Planetary Change 11: 95-109.

Ueda, H., Iwai, A., Kuwako, K. and Hori, M.E. 2006. Impact of anthropogenic forcing on the Asian summer monsoon as simulated by eight GCMs. Geophysical Research Letters 33: 10.1029/2005GL025336.

Wang, H. 1994. The monsoon precipitation variation in the climate change. Acta Meteorologie Sinica 9: 48-56.

Whetton, P.H., Fowler, A.M., Haylock, M.R. and Pittock, A.B. 1993. Implications of climate change due to the enhanced greenhouse effect on floods and droughts in Australia. Climatic Change 25: 289-317.

Whetton, P.H., Rayner, P.J., Pittock, A.B. and Haylock, M.R. 1994. An assessment of possible climate change in the Australian region based on an intercomparison of general circulation modeling results. Journal of Climate 7: 441-463.

Zhao, Z. and Kellogg, W.W. 1988. Sensitivity of soil moisture to doubling of carbon dioxide in climate model experiments, Pt. 2, Asian monsoon region. Journal of Climate 1: 367-378.

Zwiers, F.W. and Kharin, V.V. 1998. Changes in the extremes of the climate simulated by the CCC GCM2 under CO2 doubling. Journal of Climate 11: 2200-2222.