Shadowing the glaciers

No.11025350 ViewReplyOriginalReport
How much light do you need to take away to make the glaciers grow back?

Let's say you have a local mountain range of about 1000 km2. How many balloons do you need to fly over it to have a significant effect. Assume high altitude and reflectivity so all captured light goes back out.

According to the following link, the space based concept is targetting a reduction of 1.7% of sunlight to counter a doubling of CO2. (We're not there yet though)
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4550401/

Now with a small localized area, this might not be enough due to incoming winds of adjacent areas.
But what would be?