Many scientists are puzzled as to why the thermosphere is contracting. The upper most layer of the earths atmosphere begins 80 to 90 kilometers above the surface and extends several hundred kilometers into the sky. This region is occupied by numerous satellites and the International Space Station.
In a recent study of satellite orbital decay (due to light atmospheric drag) found that the contraction during 2008 and 2009 was unusually more severe than expected, leaving researchers at a loss for how to explain it.
Nevertheless the following video/animation clip, from NCAR scientist Stan Solomon offers us his theory as to why the thermosphere is contracting.
"With anthropogenic activities there has been an increase in global carbon emissions. The concentration of CO2 in the thermosphere has therefore increased. When the CO2 atoms are energized in the thermosphere by collisions with other atoms and molecules, their energy is radiated as heat before it can transfer its energy by other means such as another collision. Over time this manifests itself as an overall cooling and contraction of the thermosphere." Source
