Like most junk science, it's based partly on fact. Fog dispersal operations were being conducted at English airbases back in WWII, and cloud seeding experiments have been conducted as early as 1903, so weather modification is certainly possible, though on a very limited basis.
This has led to more adventurous experiments, and some wild rumors. There was some thought of steering a hurricane, by selectively seeding a single quadrant of the storm, back in the 1960's. However, it was determined that even if all the assets at the disposal of the United states Air force were used, there would be little or no effect. Water temperature, both on the ocean surface and aloft, is really the guiding force, and seeding would have no noticeable effect on the storm. And even if it did have some effect, it would be impossible to determine what effect the seeding operation had on it. To my knowledge, no actual experimentation was ever conducted.
That hasn't stopped the rumors from flying, though. The President of Guatemala claimed in 1967 that a hurricane that threatened the Texas coastline was moved west to hit Guatemala, with heavy loss of life. Rumors flew even more in 1969 (I believe), when a hurricane unexpectedly split in two, and became two hurricanes. This had never been observed before, and rumors quickly developed that the Air Force was somehow responsible. It wasn't.
There have been other conspiracy theories. One of Michael Crichton's last novels revolved around a rather fantastic plot by environmentalists(!) to induce earthquakes, and environmentalists have even claimed that Hurricane Katrina was somehow induced by the burning of fossil fuels.
So, it really doesn't surprise me that the United Nations, (who, to my knowledge, doesn't employ a single scientist or weather forecaster) would take up this cause. It beats doing real work, which is actually probably a good thing. Keep them involved with meaningless crap like this, and we won't have anything to fear from them.
Finally, Mad Coyotee is right. I'll move this to the UPN forum.
Onward and upward,
airforce