Radiative forcing due to trends in stratospheric water vapour

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 H 2 O 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 vapour 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.