http://eol.jsc.nasa.gov/EarthObservatory/ThinningUpperAtmosphere.htm
The below text is from the above URL. By the way, the real reason behind the
increase in Carbon Dioxide in the composition of the outer atmosphere is
DEFORESTATION.
[Models predict that emissions of carbon dioxide are causing the upper
atmosphere to cool and contract, and therefore reduce the density of gases in
the layer spanning from 90 to 649 km (60 to 400 miles) above the surface—known
as the thermosphere. According to a study by the Naval Research Laboratory
(http://www.agu.org/sci_soc/prrl/prrl0406.html), the density of the thermosphere
has decreased about 10 percent over the last 35 years. These findings are
important both for space science and for Earth science. Spacecraft in orbit,
such as the International Space Station, experience less drag and need fewer
boosts to maintain their orbit. At the same time, space debris also remains in
orbit longer, which increases hazards to spacecraft. Most importantly, the study
validates models of the “greenhouse effect” of increased carbon dioxide release
on the dynamics of the atmosphere.
Astronaut photograph ISS008-E-8951 was taken using a Nikon digital camera with
an 800-mm lens and was provided by Julie A. Robinson, Earth Sciences and Image
Analysis Laboratory (Lockheed Martin), Johnson Space Center. The International
Space Station Program supports the laboratory to help astronauts take pictures
of Earth that will be of the greatest value to scientists and the public, and to
make those images freely available on the Internet. Additional images taken by
astronauts and cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut
Photography of Earth.]