By Dan Albritton, NOAA Aeronomy Laboratory

The United Nations Montreal Protocol on Substances that Deplete the Ozone Layer was signed in September, 1987. It entered into force in January, 1989, thereby beginning a decade of decision making associated with protection of the Earth's ultraviolet-radiation shield and thereby creating the need for sound, independent, and regular information upon which to base those decisions.

Specifically, the Montreal Protocol established three Assessment Panels, with the following foci: (i) the science of the ozone layer, (ii) the environmental impacts of ozone depletion, and (iii) the mitigative technologies and associated economics. These Panels have provided the Protocol with a series of four major assessments: 1989, 1991, 1994, and 1998. The assessment process is as follows. The Panel Chairs participate in the meetings of the Parties to the Protocol, which are also attended by industry, environmental groups, and other relevant organizations. Thereby, the Chairs are able to construct a picture of the evolving information needs of the stakeholders associated with the Protocol. Periodically (about every 3 to 4 years), the Panels organize a two-year process of assessing the current state of understanding, namely, defining the information needs, organizing the drafting and peer review of an updated status report prepared by the relevant communities, and summarizing the resulting major points to the Parties in decision-relevant terms.

The 1998 State-of-Understanding Assessments

An example of a tangible "product" of the most recent assessment process is the Scientific Assessment of Ozone Depletion: 1998 (UNEP/WMO, 1999), which has been distributed to 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, has been a factor in the lower-than-usual (25-30%) ozone levels, caused by ozone-depleting gases.
  
  
• Over the midlatitudes of both hemispheres, the decadal downward trend of ozone has slowed since about 1991.
  
  
• The 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 Executive Summary of the Ozone Assessment has been separately published. This booklet also contains a section called "Frequently Asked Questions About Ozone", as well as a full list of the hundreds of international participants who contributed to the preparation and review of the Assessment. The purpose of the Summary is, of course, to give the 1998 "bottom lines" in a user-friendly format. The "Frequently Asked Questions" have been updated. It 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 ones that the public is now posing ("Is the ozone layer expected to recover? If so, when?"). Because the answers are written for the general reader, but are based upon the science embodied in the 1998 assessment, these booklets have proven useful in communicating with the public on a complex topic.

In addition to their three individual reports (UNEP/WMO, 1999; UNEP, 1999a; UNEP, 1999b), the co-chairs of the three Assessment Panels have prepared a Synthesis Report (UNEP, 1999c), which integrates the major points of their full reports. As such, it is "one-stop shopping" for the Parties regarding the overall 1998 understanding of the ozone depletion issue.

Lastly, the year 1999 marks the 10th anniversary of the formation of the Assessment Panels by the Montreal Protocol. It also ends the first decade of the Panel's providing assessed information to the world governments about the ozone layer and related topics. Therefore, the main body of the 1998 report takes this 10-year perspective in synthesizing the work of the Panels and the communities represented.

The Assessment Process: What Have We Learned?

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. Others have noted their value and style. For example, the American Library Association recognized the 1991 scientific assessment report as the Best Government Publication of that year. More importantly, 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 perspective 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 perspective 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.

The Past is Prologue to the Future
In the last section of the Synthesis Report, the Montreal Protocol Assessment Panels paused to describe "the world that was avoided"; namely, to give a forecast of what would have occurred had there been no Montreal Protocol. The nature of that world -- for example, the impacts of ultraviolet radiation on humans -- underscores the high value of the efforts of so many people worldwide who are wrestling with the series of challenging decisions and actions that are associated with the complex ozone depletion issue. In this case, the independent, professional, and regular assessments have been, by design, useful "touchstones" for society's decision making process.

References for further information (and http://www.unep.org/ozone):

• UNEP/WMO, 1999. Scientific Assessment of Ozone Depletion: 1998, pp. 732.
• UNEP, 1999a. Environmental Effects of Ozone Depletion: 1998 Assessment, pp. 191.
• UNEP, 1999b. 1998 Report of the Technology and Economic Assessment Panel, pp. 286.
• UNEP, 1999c. Synthesis Report of the Scientific, Environmental Effects, and Technology and Economic Assessment Panels of the Montreal Protocol, A Decade of Assessments for Decision Makers Regarding the Protection of the Ozone Layer: 1988 - 1999, pp. 161.