Precipitation is part of earth's self regulating processes, where atmospheric water vapor (not only from direct solar exposure but from wind, ambiance heat and nighttime evaporation as well) is returned to the surface in liquid form (rain) or ice (snow or hail); this is called the hydrological cycle or water cycle.
The WHOLE of this complex process is how Earth cools itself!
Clouds play a big role in regulating earths temperature, thick fluffy clouds truly cool the planet by reflecting sunlight, while the existence of 'clear sky' gaps between them allow the 'escape' of trapped infrared heat; while thinner more uniform and expansive clouds warm the planet by allowing heat to reach the surface while trapping the outgoing long wave radiation (green house effect).
But that is not the end of the story... the processes of cloud formation and precipitation trough evaporation  and condensation  also play important roles by themselves in this regulating effect.
Temperature, moisture and the presence of condensation nuclei are factors that lead to the formation of clouds and precipitation.
Rain occurs when condensation nuclei gather enough water droplets "with a fall velocity which exceeds the cloud updraft speed, then it will fall out of the cloud as precipitation". 
Accidental or otherwise ocean and atmospheric geoengineering, throws Earth's self regulating system, perfected over thousands of years, further 'out of whack' by injecting 'nuclei' or fertilizing materials of the wrong kind or in the wrong proportions and in the wrong places.
Injecting cloud nuclei with the purpose of maintaining or enhancing the cloud cover means less rain, which may in turn interact synergically with other lack of rain problems.
There is no logical case for geoengineering as a last resort or plan b. At present geoengineering is not palliative medicine, is euthanasia; we should rather work on solutions for all of the living.. present and future.
The truth, the real real... real truth about geoengineering or climate engineering is that it's been in our past, it is present now an will be in our future, the only question is what will it's future history be.
The most terrifying thing about GE/climate Enggineering may not be the technology itself  but some of the other questions:
Who wields it?
With what purpose?
What level of competence and trustworthiness?
Is it part of master economic or military plans with entrepreneurial and geopolitical considerations first?
All so that fossil fuels remain as the preferred method of energy generation and consumption?
The prognosis is no good.
Note (added 3/26/14)
Perhaps it would be useful to note that we are already disturbing the hydrological cycle trough our emissios of CO2, but also very large but often ignored sulfur emissions. See my more recent blog entries:
H2SO4 (SULFURIC ACID) FROM AVIATION MAY BE HIGHER TODAY THAN WHAT WOULD BE REQUIRED FOR A GEOENGINEERING REGIME IN 2020
Shipping emissions can lead to high local ocean acidification
 Effects of Turfgrass Evaporation on External Temperatures of Buildings J. L. Heilman and R. W. Gesch http://www.ars.usda.gov/SP2UserFiles/Place/36450000/Products-Reprints/1991/1211.pdf
 Latent Heat of Condensation http://www.springerreference.com/docs/html/chapterdbid/330823.html
 The Water Cycle: Precipitation http://ga.water.usgs.gov/edu/watercycleprecipitation.html
 Aerosols, Climate, and the Hydrological Cycle
V. Ramanathan1,*, P. J. Crutzen1,2, J. T. Kiehl3, D. Rosenfeld4
"Human activities are releasing tiny particles (aerosols) into the atmosphere. These human-made aerosols enhance scattering and absorption of solar radiation. They also produce brighter clouds that are less efficient at releasing precipitation. These in turn lead to large reductions in the amount of solar irradiance reaching Earth's surface, a corresponding increase in solar heating of the atmosphere, changes in the atmospheric temperature structure, suppression of rainfall'
 Desert dust suppressing precipitation: A possible desertification feedback loop
 Blue sky thinking
Geoengineers are would-be deities who dream of mastering the heavens. But are humans the ones who are out of control?
By Adam Corner
Other resources (updated 3/26/2014):
The Ocean’s Cooling Effect: An Air Conditioner for the Planet
Roberto Mera, scientist and Kendall Science Fellow - March 26, 2014
On the Role of Climate Forcing by Volcanic Sulphate and Volcanic Ash
Advances in Meteorology
Volume 2014 (2014), Article ID 340123, 17 pages
Rain Falling on Mountains Speeds CO2 Removal
By Tim Radford, Climate News Network January 26th, 2014
LONDON – U.S. scientists have measured the rate at which mountains make the raw material for molehills – and found that if the climate is rainy enough, soil gets made at an astonishing speed. And in the course of this natural conversion of rock to fertile farmland and forest loam, carbon is naturally removed from the atmosphere.
Water evaporated from trees cools global climate
Video from CarnegieInstitution:
(low cloudiness from evaporation)
Ken Caldeira: 2:15 "For each unit of energy that went into evaporating water, approximately 3/4 of a unit of energy of sunlight was reflected back to space"
How far can climate change go?
Why Does Earth Have Deserts?
Reduced efficacy of marine cloud brightening geoengineering due to in-plume aerosol coagulation: parameterization and global implications
G. S. Stuart et al.
Image from: The Water Cycle http://ga.water.usgs.gov/edu/watercycle.html
Aerosol pollution slows winds, reduces rainfall
BY MARIA JOSÉ VIÑAS
Earth Systems Science Education Alliace http://essea.strategies.org/