Roles of the Stratosphere in Climate

Marvin Geller with his colleague Marie-Lise Chanin led the successful launch of the SPARC Project within the World Climate Research Programme. SPARC stands for Stratosphere-troposphere Processes And their Role in Climate and the project began in 1992. Marv and his colleagues foresaw an important role for chemical changes associated with the developing stratospheric ozone hole on polar temperatures, general circulation, and climate. He served as Co-Chair of the SPARC Scientific Steering Group for 10 years from the project's inception until 2002. At the beginning of SPARC, a time when the stratosphere was widely considered irrelevant to climate, and the importance of resolving stratospheric processes in climate models was still a crazy idea, Marv and Marie-Lise championed the idea and forged a a project now entering its 24th year that has had a remarkable international influence. Today, a clear measure of SPARC's success lies in the fact that most of the climate models participating in the Coupled Model Intercomparison Project (CMIP) for the assessment of the Intergovernmental Panel on Climate Change include stratospheric processes. A number of important issues have emerged that have lead SPARC to continually broaden its range of international collaborative projects: Representing ozone depletion and its expected recovery is a key element in models seeking to understand recent and future climate changes in the Southern Hemisphere; Stratospheric volcanic aerosols are recognized as a major source of variability in the surface temperature record; Changes in stratospheric water vapor are understood to be a key uncertainty in decadal-scale climate change; The stratospheric quasi-biennial oscillation in zonal winds is known to modulate tropical-extratropical teleconnections and regional patterns of climate variability; Sudden stratospheric warnings are a source of significant subseasonal climate predictability. These and other examples illustrate the scientific successes of the SPARC Project and the SPARC community that Marv's work and vision fostered.