Evidence of long term global decline in the Earth's thermospheric densities apparently related to anthropogenic effects

A study was performed of the long-term orbital decay of five Earth satellit es with perigee altitudes averaging near 350km. To decouple long-term trend measurements from the effects of solar variability, measurements were eval uated during the years of solar minimum (1976, 1986 and 1996). Atmospheric densities derived from these essentially global measurements showed substan tial evidence of a decline averaging 9.8 +/- 2.5% in thermospheric density over 20 years pointing toward a long-term cooling of the upper atmosphere. Increases in greenhouse gases induced by human activity are hypothesized to warm the Earth's surface and lower atmosphere, but strongly cool the upper atmosphere. Assuming that the 10% increase in CO2 over these 20 years caus ed cooling resulting in the 10% decline in density, a doubling of CO2 could cause the thermospheric densities measured near 350km to decrease by a fac tor of 3. This decrease may shrink the altitude of a constant density surfa ce by 40km before the end of the 21(st) century.