Climate models predict that the concentration of water vapour in the Upper Troposphere (UT) could double by the end of the century as a result of increases in greenhouse gases. Observations indicate that the height of the tropopause has increased by several hundred meters since 1979. We try to reconcile these two trends by using the rather uniform dataset of radiosonde vertical profiles we gathered at Uccle since 1990. This dataset can form the basis for a time series analysis of the humidity field in the upper troposphere. We found that the UT layers above Uccle are going down between January 1990 and September 2001, hence warming up, which results in a moistening. After September 2001, the UT layers are lifting, cooling down and (slightly) drying. Other authors also pointed to a change in the Brewer-Dobson circulation around this year. However, we argue that the movement of the UT layers above Uccle (and by extension above the European continent, as we will show) is rather due to the dynamics of the underlying troposphere, which in turn is governed by the temperature variation at the surface.- ABSTRACT???