i would be interested in what/where those "controlled experiments" were... my understanding is that even experimenting is a no no in the field of geoengineering. Versus reflective schemes this actually "removes" carbon and is thus is a net gain, not merely a partial temporary cover. It also increases biota -- exactly the opposite of what humans tend to do, we are now in a major extinction event. Increasing biota on land is very hard and unlikely, but this easily increases it in the seas where it is badly needed. It is also easily titrated - one can stop/in/de/crease adding Iron and Phosphorus at any time.