In late winter (February and March), there is a trend in the cooling of the polar stratosphere as well as declining wave activity in both the lower stratosphere and the troposphere. The question is : Is the decadal cooling in the stratosphere caused by a decline in wave activity from the troposphere, or is the decline in wave activity caused by readiatively induced cooling occurring in the polar stratosphere? Sorting out the cause and effect is the focus of this work. We will show using NCEP data and TOMS ozone that the planetary wave trends in the lower atmosphere are likely induced by changes in the zonal mean waveguide in the stratosphere caused by ozone induced cooling. Using quantitative arguments, we show that on decadal time scales, the observed cooling trend in the stratosphere cannot be accounted for by declining wave activities. However, the stronger polar vortex resulting from the cooling yields a change in the index of refraction for planetary waves which are consistent with the trends in wave activity in the lower atmosphere.