The scientific community and society have placed increasing importance on the consequences of potential global warming. At the forefront of these issues is the fate of the global water cycle, which includes (among others) changes in patterns, intensity and/or frequency of precipitation events. However, the complexities and interplay of precipitation (microphysical) processes are represented quite differently among state-of-the-art general circulation models (GCMs). Further, GCMs' projections of anthropogenic warming are challenged by uncertainty in global climate sensitivity as well as inaccuracies in their implied rates of global deep-ocean heat uptake. As a result, quantifying the range of possible mean precipitation changes due to (uncertain) global warming is inherently difficult and recent results of event-based precipitation assessments from GCMs prove to be at least equally uncertain and, in some cases, contradictory. Nevertheless, observational analyses suggest that we have seen significant shifts in the occurrence of (extreme) precipitation events within the past century. The MIT Integrated Global System Model (IGSM) is designed for analyzing the global environmental changes that may result from anthropogenic causes, quantifying the uncertainties associated with the projected changes, and assessing the costs and environmental effectiveness of proposed policies to mitigate climate risk. We present results from our latest large ensemble of runs that span multiple dimensions of climate-change uncertainty. In particular, we focus on a sub-sample of runs that address the uncertainty of precipitation-frequency change. The range of the uncertainty in changes in precipitation-frequency are based upon analyses of experimental results from nearly a dozen state-of-the-art GCMs taken from IPCC's AR4 archive. Particular attention will be placed on the impact of the uncertainty in precipitation-frequency change on the range of changes in: trace-gas emissions and productivity from global natural (and managed) ecosystems, as well as continental water and energy fluxes. In addition, the influence of various prescribed climate policies on these hydro-ecologic impact scenarios will be assessed.