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Foreword

This scientific assessment has been carried out jointly by the WCRP project on Stratospheric Processes and their Role in Climate (SPARC) and the International Ozone Commission (IOC), in close co-operation with WMO’s Global Atmospheric Watch programme (GAW). The objective of the report is to review critically the measurements and trends of the vertical distribution of ozone. Recently revised data are used where appropriate and the time period covered has been extended into mid 1996. This objective has been achieved, and this report contains a thorough description of the measurements and their associated uncertainties as well as the trends and their associated uncertainties. The executive summary, which follows, first appeared in SPARC Newsletter No. 10 during the spring of 1998.

This is the first assessment of its kind carried out by SPARC and the IOC. It was stimulated by the WMO/UNEP Scientific Assessment of Ozone Depletion : 1994 which found large discrepancies between ozone trends in the lower stratosphere. One of the objectives of this assessment was to ensure a continuity in the international effort necessary to prepare the WMO/UNEP Assessments and the work presented here is being heavily relied on in the production of the 1998 assessment. It is also being used in the preparation of the Special IPCC Report on Aviation and the Global Atmosphere. The SPARC-IOC-GAW assessment also anticipates the need for precise updated observations of the vertical distribution of stratospheric ozone depletion to be used to assess the impact on climate in the Third IPCC Assessment Report on Climate Change due in the year 2000.

The need for such an assessment was recognised by the IOC, SPARC and GAW in 1995 after the publication of the 1994 WMO-UNEP Assessment. The outline of the assessment was determined by an international group of scientists during a workshop held at the Observatoire de Haute Provence in France, in July 1996. The drafts of the chapters were prepared in the following year and an impressive amount of new critical analyses were produced. The draft report was examined by an international panel of reviewers both by mail peer review and at a meeting at Abingdon, United Kingdom in October 1997. This rigorous review greatly improved the report, especially the presentation of the large amount of new material and the consistency between chapters.

The success in producing the present document is the result of the intensive work and enthusiastic co-operation of a large number of scientists world-wide who have worked towards improving the quality of the measurements, validating the trends observed with state of the art techniques, and calculating and validating the trends deduced, testing the models used. This has resulted, for the first time, in a single profile of observed ozone depletion at northern mid-latitudes, combining all the observing systems available. The work of the contributors and reviewers was generously supported by many agencies including WMO-GAW, WCRP, SPARC, DG-XII of the European Commission, NASA, NOAA, UK DETR, CNRS and other national research programmes and institutions.

We take this opportunity to express our gratitude to all the scientists (authors, contributors and reviewers) who helped in the preparation this assessment and to the SPARC and IOC panel members who have been supportive since its inception. Our special gratitude is due to the lead authors of the chapters who worked impressively hard and effectively. Particular thanks must be given to Isabelle Faviez of the Institut Pierre Simon Laplace, France, who helped organise the workshop at the Observatoire de Haute Provence, and Maria Brown of the European Ozone Research Co-ordinating Unit, United Kingdom, for her help in organising the workshops and the final editing of the report. Finally, and by no means least, we sincerely thank our co-editor, Céline Phillips of the SPARC office, for her dedicated hard work at all stages during the preparation of the report, at the meetings and especially in the preparation of the final document.

Neil Harris, European Ozone Research Coordinating Unit , Centre for Atmospheric Science, University of Cambridge, UK
Bob Hudson, Department of Meteorology, University of Maryland, USA Assessment co-chairs.