Pumping crap into the air to cool things off has been suggested as a way of countering global warming. A new paper by Kevin Trenberth and Aiguo Dai at NCAR makes this look like a bad idea. They used actual volcanic eruptions as an analog and looked at their effect on the hydrologic cycle:

Following the eruption of Mount Pinatubo in June 1991 there was a substantial decrease in precipitation over land and a record decrease in runoff and river discharge into the ocean from October 1991–September 1992. The results suggest that major adverse effects, including drought, could arise from geoengineering solutions.