No. First, there is not enough up there to impact the amount of solar energy coming into the top of the atmosphere. Space junk is very small and space is very big. [There are 300,000 pieces larger than 1 cm estimated to exist below 2,000 kilometres (1,200 mi).](https://en.wikipedia.org/wiki/Space_debris) Adding that up into a single sheet would be 3000 square meters, which at 500 miles up would be about 1.25 arc minutes wide. This is about the size of a small planetary nebula in the night sky, or about the size of the crater Copernicus on the moon. Translation, you would see it, but barely as a fuzzy source of light at the limit of normal human eyesight, about as bright as the space station on a favorable pass. This is assuming that the debris formed a sheet 1cm thick and was uniformly flat and tangent to the earth's surface.

More info about space debris here.

The bigger impact is aerosol levels in the upper atmosphere.These reflect light back into space. One of the factors commonly "blamed" on the sharp rise in global temps over the last 30 years is the reduction in aerosol pollutants in the upper atmosphere. But! Aerosols cause clouds as well, and clouds trap heat. When you add the two, they nearly balance out. One group was suggesting dumping a bunch of bright pollutants into the stratosphere to cool the globe, but hopefully we stop and think before we go crazy and mess with the whole planet's ecology.