Maybe attaching lasers to baby birds will make it rain
There appears to be a laser technology that can be fired into the atmosphere to induce cloud formation processes. [http://www.nature.com/news/2010/100502/full/news.2010.213.html?s=news_rss] A "few" challenges remain to take the step from producing some droplets in the path of the beam to producing measurable rainfall. Whether there are any unexpected consequences is an open question. One potential issue is what happens high up in the atmosphere? The way this works is that the laser ionizes oxygen and nitrogen, which then somehow act as condensation nuclei. What happens in the stratosphere when you create ions? I don't know the answer, but I do know that there is a lot of chemistry happening in the stratosphere. We might not to perturb that chemistry if we don't understand the consequences. See also ozone depletion.