Can ozone depletion and global warming interact to produce rapid climate change?

The atmosphere displays modes of variability whose structures exhibit a str ong longitudinally symmetric (annular) component that extends from the surf ace to the stratosphere in middle and high latitudes of both hemispheres. I n the past 30 years, these modes have exhibited trends that seem larger tha n their natural background variability, and may be related to human influen ces on stratospheric ozone and/or atmospheric greenhouse gas concentrations . The pattern of climate trends during the past few decades is marked by ra pid cooling and ozone depletion in the polar lower stratosphere of both hem ispheres, coupled with an increasing strength of the wintertime westerly po lar vortex and a poleward shift of the westerly wind belt at the earth's su rface. Annular modes of variability are fundamentally a result of internal dynamical feedbacks within the climate system, and as such can show a large response to rather modest external forcing. The dynamics and thermodynamic s of these modes are such that strong synergistic interactions between stra tospheric ozone depletion and greenhouse warming are possible. These intera ctions may be responsible for the pronounced changes in tropospheric and st ratospheric climate observed during the past few decades. If these trends c ontinue, they could have important implications for the climate of the 21st century.