........ published in NEWSLETTER # 49
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........ published in NEWSLETTER # 49
THE ROLE OF THE STRATOSPHERE IN GLOBAL CHANGE
by Dr. M._L. Chanin, CNRS, Verriers_Le_Buisson (France)
A NATO Advanced Study Institute organised in Carqueiranne, France, in 1992 was aimed at describing how the stratosphere and its on_going perturbations may have an impact on the climate and on the biosphere. The book (NATO ASI SERIES I8) contains most of the lectures and deals with the aspects of global change encountered by the stratosphere and of their consequences on the troposphere_stratosphere system. It focused first on the basic processes taking place in the stratosphere and on the stratospheric changes which may occur either from natural (solar, volcanic ...) or anthropogenic forcing. This region is shown to be one of the most fragile parts of the geosphere. An illustration of this is the appearance of the Antarctic Ozone Hole in which fully half of the Antarctic Spring column ozone has disappeared during the past dacade. Although it is now well established that polar stratospheric clouds (PSCs) interacting with man released chlorine and bromine species are causing this depletion, key questions related to global consequences of similar processes occurring at Northern latitudes and in connection with stratospheric aerosols, mostly since the observed impact of the recent Pinatubo eruption, were discussed.
Another important issue is how the stratospheric changes may impact the troposphere. It has been long understood how important tropospheric processes are in determining the structure of the stratosphere. It is less well understood how stratospheric processes affect tropospheric climate; however, it is becoming increasingly clear that the stratosphere cannot be ignored in considering climate change. Many of the same gases that are responsible for greenhouse warming of the troposphere are imporatant for ozone photochemistry. Since ozone is itself a greenhouse gas, changes in stratospheric ozone must be considered in assessing future climates resulting from greenhouse warming. Models of the present state of the coupled stratosphere_trophosphere system and predictions of its future state are presented.
One of the expected consequences of change in the stratospheric composition, mainly the Ozone depletion, is the change in the penetration of UVB in the troposphere, at the surface, and in the top layers of the ocean. Monitoring and modelling of those changes are still in infancy, even though the implication may be of utmost importance for the whole biosphere. Several aspects of these consequences on aquatic ecosystems, terrestrial vegetation and human health were presented by biologists, who are experts in these different fields.
The publication of such a book is very timely, especially considering the recent implementation of a new WCRP (World Climate Research Programme) Project entitled SPARC (Stratospheric Processes and their Role in the Climate), and initiatives it gives rise to in the atmospheric community. It will be a basic reference text book for those who are starting to be involved in the programme. It will be followed by workshops on more specific subjects such as Stratosphere_Troposphere Exchange, Volcanic forcing, Solar influence on Climate, etc.
Reference books: C227, G8, I7, I8