Using Geoengineering to cool the climate to the point of collapse is going to be significantly more difficult than heating the planet to accomplish the same means.
The basic idea involves spraying Calcium Carbonate dust into the upper atmosphere to reflect a fraction of incoming sunlight before it has a chance to get trapped and absorbed.
How effective this is depends on how much dust you can disperse, how much light it actually reflects away, and how long it persists in the upper atmosphere.
The point of this study is to test to see if they can determine any of those values (and of course to see if they can assess the biological safety).
Some assumptions we can make are: The dust won't be SUPER effective at blocking light, the dust won't stay there for a very long time, and it will therefore take a LOT of dust to be even partially effective.
We're talking about dedicating a sizeable fraction of our global industrial capabilities to harvest the raw materials, process it into super-fine dust, and then fly it many miles into the sky.
The effort will undoubtedly take many years and will RELEASE a ton of additional CO2 into the atmosphere.
It would not be possible to accomplish this in the sneaky "evil overlord quietly gets a dooms-day device in place".
You'd be much better off trying to heat the planet up, since that's the trajectory we're currently on.
If you are insisting on accomplishing Global Cooling on a catastrophic level, consider attempting to jump start a super volcano such as Yellowstone.