Trends derived from the latest version of Halogen Occultation Experiment (HALOE) data are used in a two-dimensional atmospheric model to estimate their radiative effects over the last decade. The results show a stratospheric cooling in regions of H2O increase, of magnitude similar to that due to stratospheric ozone loss indicating a significant additional cause of observed stratospheric temperature decreases. Radiative forcings are derived and it is found that global average radiative forcing due to stratospheric water vapor changes probably lies in the range 0.12 to 0.20 Wm-2 decade-1. This could have more than compensated for the negative radiative forcing due to decadal ozone loss. ¿ 2001 American Geophysical Union