SCIENTIFIC ASSESSMENT OF STRATOSPHERIC OZONE DEPLETION
Some recent scientific assessments have played critical roles in summarizing the state of scientific knowledge
in a fashion that allowed policy-makers to make informed decisions and that stimulated the acquisition
of additional knowledge (questions 1-5 in the text). For example, a series of international scientific assessments
on stratospheric ozone articulated the dimensions of a formerly unappreciated environmental
problem; indicated the certainties, uncertainties, and priority areas for further research; and evaluated the
likely consequences of various policy options. These assessments led to international agreements to limit
production of stratospheric ozone-reducing compounds, a major environmental success story.
A series of international scientific assessments between 1985 and 1998 provided credible and integrated
summaries of the state of knowledge on stratospheric ozone. During this interval and driven in part by the
assessment process, significant advances were made in the understanding of the impact of human activities
on the ozone layer, the influence of changes in chemical composition on the radiative balance of Earth's
climate, and the coupling of the ozone layer and the climate system itself.
The fifth scientific assessment of ozone depletion was published in 1998 (WMO/UNEP 1998) in response to
provisions of the 1987 Montreal Protocol on Substances That Deplete the Ozone Layer. The protocol
required that future decisions be based on the available scientific, environmental, technical, and economic
information as assessed by worldwide expert communities. The scientific assessment articulates 11 major
scientific findings and observations, among them:
The abundance of ozone-depleting compounds in the lower atmosphere peaked in about 1994 and is now slowly declining.
The springtime Antarctic ozone hole continues unabated.
Stratospheric ozone losses have caused a cooling of the global lower stratosphere and may have offset about 30 percent of the climate forcing due to increases in the well-mixed greenhouse gases such as carbon dioxide and methane.
The assessment details the supporting scientific evidence for its findings and discusses related issues and
needed research. It then provides an analysis of implications for policy formulation, including discussion of
The Montreal Protocol is working.
The ozone layer is currently in its most vulnerable state.
The ozone layer will slowly recover over the next 50 years.
Few policy options are available to enhance the recovery of the ozone layer.
The issues of ozone depletion and climate change are interconnected; hence, so are the Montreal and Kyoto Protocols.
The scientific assessment of ozone depletion is an excellent example of a scientific assessment whose outcome was a significant benefit to the world.