There is apparently a kind of bacteria that can cloud seed. I don't recall how it gets up into the air, but it has some biochemistry that increases the dew point by a few degrees celcius, and then rides the rain back to the ground.

We may find that seeding the stratosphere with one of these bacteria, especially if this happens again when we are farther down the Climate Change rabbit hole, is more ecologically sound than stuffing aerosols up there.