NCAR - Thermosphere (Outermost Atmospheric Layer) Thinning Thanks To Climate Disruption

[hatrack]

BOULDER—Carbon dioxide emissions from the burning of fossil fuels will produce a 3 percent reduction in the density of Earth's outermost atmosphere by 2017, according to a team of scientists from the National Center for Atmospheric Research (NCAR) and The Pennsylvania State University (PSU). The research, which appears in the latest issue of Geophysical Research Letters, will be presented today at the annual meeting of the American Geophysical Union.

"We're seeing climate change manifest itself in the upper as well as lower atmosphere," says NCAR scientist Stan Solomon, a co-author of the study. "This shows the far-ranging impacts of greenhouse gas emissions." The research team includes Solomon, Liying Qian, and Ray Roble of NCAR’s High Altitude Observatory; and Tim Kane of PSU. The study was supported by NASA’s Living With a Star program and by the National Science Foundation, NCAR's primary sponsor.

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Confirming and extending a prediction

Recent observations by scientists tracking satellite orbits have shown that the thermosphere, which begins about 60 miles above Earth and extends up to 400 miles, is beginning to become less dense. This confirms a prediction made at NCAR in 1989 by Roble and Robert Dickinson (now at the Georgia Institute of Technology) that the thermosphere will cool and contract because of increasing carbon dioxide levels. The new study is the first to analyze whether the observed change will become more pronounced over the next decade.

Why the cooling is a sign of global warming

Carbon dioxide cools the thermosphere, even though it acts to warm the atmosphere near the Earth's surface (the troposphere). This paradox occurs because the atmosphere thins with height. Near the Earth's surface, carbon dioxide absorbs radiation escaping Earth, but before the gas molecules can radiate the energy to space, frequent collisions with other molecules in the dense lower atmosphere force the carbon dioxide to release energy as heat, thus warming the air. In the much thinner thermosphere, a carbon dioxide molecule absorbs energy when it collides with an oxygen molecule, but there is ample time for it to radiate energy to space before another collision occurs. The result is a cooling effect. As it cools, the thermosphere settles, so that the density at a given height is reduced.

EDIT

http://www.ucar.edu/news/releases/2006/thermosphere.shtml

[YankeyMCC]

1. Stupid question

If the layer is contracting or settling wouldn't that make increase the density at any given height, although the overall thickness would be less?