The largest atmospheric temperature changes due to the increase of greenhouse gases are expected in the 40 to 60 km altitude region, where enhanced infrared cooling decreases the temperature. Ten-year (1980--1990) temperature trends at 55 km and 0.4 mb, derived using data from the ground-based lidar at Haute Provence, 44 ¿N 6 ¿E, and the SSU channel 47X on several satellites, are presented. These data show temperature decreases that are as large and in some cases exceed predictions based on current models. At 44 ¿N, the ground-based lidar and satellite techniques give a negative trend of -0.10¿0.04% per year and -0.14¿0.02% per year, respectively. Agreement between these two data sets based on different measurement techniques gives confidence in the detected trends at this latitude. Further analysis of the SSU 47X satellite data between 45 ¿S and 45 ¿N indicates a maximum decline of 0.16% per year near 30 ¿N. A minimum trend decrease of 0.07% per year is detected between 20¿ and 30 ¿S. Based on NOAA satellite radiance observations, these long-term temperature changes are larger than changes at any of the other stratospheric levels below 55 km monitored during this period. ¿ American Geophysical Union 1991