Carbon dioxide heats the low atmosphere through the greenhouse effect. In the high atmosphere, however, carbon dioxide does not have enough density to cause the greenhouse effect, but absorbs heat from the area and will radiate out of the Earth. Thus, the high atmosphere cools and compresses towards Earth.
This is good news for satellites, as being lower density in the high atmosphere, they must withstand less friction and can remain in orbit for longer. But the same goes for the garbage in space.