Wednesday, December 13, 2006

Global Warming cools upper atmosphere

That headline is not a misprint. A scientific team led by Dr. Stan Solomon of the National Center for Atmospheric Research (NCAR) in Colorado reports that an odd side effect of global warming caused by greenhouse gases in the lower atmosphere is that the thermosphere, the envelope of very thin air starting at about 100 kilometers, will be cooled. The reason is that CO2 molecules collide with air molecules often in the lower atmosphere, producing heat, but are unlikely to collide with any in the thermosphere, so any heat they carry is dissipated into space.
Orbiting objects like the International Space Station will benefit from this reduction, since a cooler thermosphere is less dense and thus causes less drag. (Thermospheric drag is predicted to drop about three percent by 2017.)
Unfortunately, low-orbiting space junk and debris benefits the same way, meaning it will be a hazard to space travelers longer than expected. The other long-term effects of this cooling of the thermosphere are unknown at this time.

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