The United Nations Montreal Protocol on Substances that Deplete the Ozone Layer was signed in September, 1987. This international agreement began what is now over a decade of decision making associated with protection of the Earth's ultraviolet-radiation shield. The process created the need for sound, independent, and regular information upon which to base those decisions. Specifically, the Montreal Protocol called for periodic assessments of the understanding of (i) the science of the ozone layer, (ii) the environmental impacts of ozone depletion, and (iii) the mitigative technologies and associated economics.
The latest scientific "product" of this assessment process is the Scientific Assessment of Ozone Depletion: 1998, prepared by a substantial fraction of the ozone research community worldwide. The report is now in the hands of governments, industry, the professional communities, and interested members of the general public. The sections of the report address the major four questions about the ozone layer issue: "What's happening?", "Why?", "So what?", and "What's next?" Examples of answers include the following findings:
The total abundance of ozone-depleting gases in the lower atmosphere peaked in 1994 and is now (slowly) starting downward, giving direct evidence that the Montreal Protocol is working.
The springtime Antarctic ozone "hole" continues unabated, with the overall extent of loss being essentially unchanged since the early 1990s.
In the Arctic, six of the past nine winters have been cold and protracted, which, as predicted, have caused lower-than-usual (25-30%) ozone levels.
Over the midlatitudes of both hemispheres, the decadal downward trend of ozone has slowed since about 1991.
The peak abundance of ozone-depleting gases in the stratosphere is expected to peak before the year 2000, and the ozone layer will then be in its most vulnerable state for the next decade or two.
Detection of the recovery of the ozone layer as a result of the Montreal Protocol may not be possible for perhaps another 20 years, due to the superimposed natural variation of ozone, changing atmospheric composition, possible volcanic activity, the coupling of ozone change and climate change, and other potential human impacts on the ozone layer.
The 1998 assessment also contains an updated list of "Frequently Asked Questions About Ozone". The list still has the questions and answers that were formulated in the 1994 assessment (e.g., "If CFCs are heavier than air, how can they get to the stratosphere?"), but it also includes questions that the public is now posing ("Is the ozone layer expected to recover? If so, when?"). Since the answers are written for the general reader, but are based upon the science embodied in the 1998 assessment, these Q&As have proven useful in communicating with the public on a complex topic.
The Parties to the Montreal Protocol have found the assessments to be essential input to decision making. Amendments and adjustments to that historic international agreement have occurred in lock step with the major assessments in 1989, 1991, and 1994. Features of the Montreal Protocol assessments have been adopted by the Intergovernmental Panel on Climate Change (IPCC) when it set up its assessment process, which issued its first report in 1990.
It is no accident that such assessment features have "caught on", since several aspects of the assessments have proven to be highly useful:
They are the integrated perspectives of the (vast) majority of the expert communities involved, which is in contrast to the more-limited utility of the viewpoint of a particular scientist, technologist, or economist.
They are the status of understanding of the information-producing communities, but that information is described in the context of the information needs of the stakeholding "customers".
They are the perspectives of the global communities on a global issue, which is in contrast to a particular national or single-sector viewpoint.
They are an end-to-end picture of the issue (causes -> effects -> options), which is in contrast to a study of a single aspect of a phenomenon/issue.
Lastly, the Protocol recognized that knowledge improves over time and hence that the assessment process must necessarily be a sequential one.
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