Darken the sky

I have been pondering the idea of fighting the greenhouse effect with nuclear winter (previous idea - linked). It is sloppy. However the idea still seems valid - if you can decrease incident radiation, you can cool the earth. Doing so by suspending particles in the atmosphere is a reversable way to achieve cooling.

Rather than blowing up bombs in the Antarctic, the same end could be more cleanly achieved with railguns. A railgun operation with a dedicated powerplant would launch small payloads up to the appropriate level in the atmosphere. Once there they would detonate, releasing microparticle mylar. These particles would do a better job at reflecting than random dirt launched by a volcano or bomb. They would do no harm on settling down to the earth over months or years. Also, the railgun could be run continuously for incremental darkening of the sky. Mistakes would not be calamatous - a $100 5 kg undetonated mylar projectile falls into the ocean, or the railgun malfunctions and must be repaired. If it turns out that dark skies are bad, give it a year or two and it will revert to normal!

Another idea about railguns - it seems like arcing and melting of the rails is a big problem. If the rails were superconducting, would this still be a problem? My understanding of a superconductor is that they do not lose energy to heat. It is heat that melts the rails and requires the gun to go offline for resurfacing. Would superconductivity avoid this? How about surfacing with carbon fiber? It does not melt, but vaporizes, which would avoid globs of congealed rail matter gumming up your rail.