You didn't quite take notes well. You missed one very important
point: the growth rates. Greenhouse gas forced global warming is
growing faster than aerosol forced global dimming. So, though
global dimming may cancel 1/2 of global warming today, it will
cancel a much less significant fraction of global warming tomorrow.
Therefore, global dimming is not the solution to global warming,
greenhouse gas emission reductions are.

The problem with your Aluminum Sequin idea remains the same. The
trick to calculate the area that needs to block the Sun. It's now a
wopping 0.2% of the Earth's cross section, or 300,000 km squared!
That figure is growing, too. Below, is my post of a few months ago.
=-=-=-=-=-=-=
Let's run some numbers on this idea . . .
The solar constant is ~1367 Watts per Meter squared
http://en.wikipedia.org/wiki/Solar_Constant
Global Warming is now about 3 watts per meter squared,
which is 0.2% of the solar constant.
http://www.giss.nasa.gov/data/simodel/
(Global Warming will quadruple in a century or two.)

The cross sectional area of the Earth is 125,000,000 km²
http://en.wikipedia.org/wiki/Solar_Constant

The area of Aluminum sequin in orbit needed to remove the current
global warming is, therefore roughly .002 * 125,000,000 km squared
or 300000 km squared.

If your sequins were one 10,000th of a meter thick, you would need
to orbit 30 km cubed worth of Aluminum.

The density of Aluminum is 2.70 g/cm³.
http://en.wikipedia.org/wiki/Aluminum

One km cubed is equal to 10 to the 15 cm cubed.

So you want to orbit 8 times 10 to the 13 the power kg
of Aluminum.

Well then, GOOD LUCK.
Even if you could reduce this by, say, making your sequins
1/1000 thiner, it would still be impossible. But . . .

I've got an idea! WHY NOT JUST REDUCE THE EMISSIONS
OF GREENHOUSE GASES? Wouldn't that be easier?
Of course, one could not write good science fiction with
this solution, because greenhouse gas reduction is just
too practical.