The GFDL SKYHI general circulation model is used to compute annual and seasonal stratospheric temperature trends and radiative forcings due to the observed changes in stratospheric ozone and greenhouse gases in the last twenty years. The computed decadal temperature trends are compared to the measured (1979-2000) trends from satellites and sondes. The relative importance of the observed ozone losses and greenhouse gas increases is evaluated through calculations in which ozone and greenhouse gases are separately changed. The computed annually and globally averaged temperature trends are similar to observed trends in the lower stratosphere, but greatly exceed the observations near the stratopause. When the GCM reference ozone and temperature climatology is computed using a 1989-91 ozone climatology, upper stratospheric temperature trends agree closely with satellite measurements. The GCM calculations indicate that ozone loss is the major cause of temperature change in the lower stratosphere while greenhouse gas change dominates in the rest of the stratosphere. In the lower stratosphere, model temperature trends are within the range of the measured trends, except in mid-latitudes of the northern hemisphere. The results indicate that anthropogenic changes in ozone and greenhouse gases largely explain the recent temperature changes in the stratosphere.