Stratospheric cooling?

One consequence of Earth undergoing greenhouse-caused warming would be a cooling stratosphere.  It i often claimed that the stratosphere, specifically the lower stratosphere, has in fact been cooling, thus confirming the enhanced greenhouse effect hypothesis.  Skeptics refute this claim in two ways: the cooling was caused by ozone depletion; and the cooling has now stopped.

Proponents of the Enhanced Greenhouse Effect theory suggest that the observed stratospheric cooling has been the product of both ozone depletion and a more intense greenhouse effect.

I recognize that the fact that the stratosphere hasn’t cooled for 13 years is an important point to make, especially considering the fact that month-to-month variation in stratospheric temperatures is small and thus trends are easy to extract.  Yet, I’ve never heard the point made that the only time the stratosphere seemed to cool was right after volcanic stratospheric warming episodes.  I’ve used paint to illustrate my point:

During the volcanic eruptions of El Chichon and Mt. Pinatubo, stratospheric temperature jumped and surface temperature fell.  Yet, instead of stratospheric temperatures returning to normal, they appear to have dropped significantly lower than they were before the eruption.  I’m not proposing any physical mechanism that could explain this, nor am I fully backing the idea that the volcanic eruptions caused the observed coooling.  I just thought it was worth noting.

UPDATE

I finally found a graph of global ozone levels (rather than Antarctic ozone levels or the size of the Antarctic ozone hole).  I’ve posted it below.

With this graph (data from here) as context, the trends in lower stratospheric temperature make sense, as caused (at least in part) by changes in ozone.  The graph appears to show diminishing ozone, with either an 11-year solar cycle!!!! or more likely the effects of bromine and chlorine released into the stratosphere by the especially intense eruptions of El Chichon and Mt. Pinatubo.