Is there Greenhouse Cooling in the Thermosphere?

Thomas Ulich and Esa Turunen

Geophysical Observatory, FIN-99600 Sodankylä, Finland


Increased concentrations of greenhouse gases in the air are predicted to cause cooling of the entire middle and upper atmosphere (Roble and Dickinson, 1989); doubled mixing ratios of carbon dioxide and methane would result in a 50 K decrease of the thermospheric temperatures. Rishbeth (1990) predicted a consequent lowering of the peak height of the ionospheric F2-layer by 20 km. Experimental evidence of a long term trend, favouring interpretation as greenhouse cooling, was shown by Bremer (1992). We compare high latitude data from Sodankylä Finland, (67.4 N, 26.7 E) with Bremer's results for mid-latitudes, and with other ionosonde records. While Sodankylä shows a linear decrease of the peak height during the last 40 years, the same trend is not observed at all locations in this study.