USGCRP logo & link to home

Updated 12 October, 2003
Depletion and Recovery of the Ozone Layer: An Update of the Scientific Understanding
USGCRP Seminar, 23 September 1998
Horizontal blue line.


What are the current and projected trends in stratospheric ozone-depleting chemicals in the atmosphere? Has the Montreal Protocol been effective in reducing ozone-depleting chemicals in the atmosphere? How severe is ozone depletion at present? Will ozone depletion worsen before it gets better? Is ozone depletion confined solely to high latitudes? Will the ozone layer recover to its natural state, and if so, when? Are there likely to be surprises along the way?


Dr. David Goodrich
Executive Director, U.S. Global Change Research Program Coordination Office, Washington, DC


Dr. Daniel L. Albritton
Director, National Oceanic and Atmospheric Administration Aeronomy Laboratory, Boulder, CO


State-of-Science Update: The Stratospheric Ozone Layer

The forthcoming United Nations Environment Programme (UNEP) report,"Scientific Assessment of Ozone Depletion: 1998" will be the newest in a series of assessments providing an update on the state of scientific understanding of the Earth's ozone layer. The key scientific points and conclusions contained within this report's Executive Summary are listed below. These key points were established and agreed upon at a peer-review meeting held in early June, 1998, of the full assessment report. Over 250 scientists from around the world participated in the writing and review of the 1998 report, which will go to press later this year and will be available in early 1999.

Key Points of UNEP's Scientific Assessment of Ozone Depletion: 1998

  • The total tropospheric abundance of ozone-depleting gases 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 extent of Antarctic ozone depletion essentially unchanged since the early 1990s.

  • In the Arctic, six of the past nine winters have been cold and protracted. As predicted in the 1994 assessment, those winters have seen lower-than-usual ozone levels in the region. Ozone has declined during some months by 25-30% below the 1960s average.

  • Over the middle latitudes of both the northern and southern hemispheres, the decadal ozone decline has slowed since about 1991. The understanding of how changes in stratospheric chlorine/bromine and aerosol loading affect ozone suggests some reasons why a linear extrapolation of the pre- 1991 ozone trend to the present is not suitable.

  • Ozone losses in the stratosphere may have caused part of the observed cooling of the lower stratosphere in the polar and upper middle latitudes (about 0.6 degrees C per decade since 1979).

  • The Ozone Depletion Potential (ODP) of methyl bromide is now calculated to be 0.4 [compared to 0.6 from the previous (1994) assessment], with the change being largely the result of the recognition and better quantification of removal mechanisms in soils and oceans.

  • In the stratosphere, the peak in the abundance of ozone-depleting gases is expected before the year 2000, and the ozone layer will be in its most vulnerable state for the next decade or two. Detection of the start of the ozone layer recovery may not be possible for perhaps another 20 years, due to natural ozone variability and changing atmospheric conditions.

  • There are not many remaining options for substantially hastening the return to a natural ozone layer. The largest of these options are associated with potential action regarding the halons, which would typically lower the sum of the ozone depletion over the next 50 years by a few to several percent. Non-adherence to the Montreal Protocol could also add to future integrated ozone depletion.


Dr. Daniel L. Albritton has directed the Aeronomy Laboratory of NOAA's Environmental Research Laboratories in Boulder, Colorado since 1986. The research of the Laboratory is focused on understanding the chemistry and dynamics of the atmosphere. Several key environmental phenomena are being addressed: stratospheric ozone depletion, regional tropospheric chemistry, tropospheric ozone production, tropical ocean/atmosphere interactions, and the climate system. The Laboratory is staffed with approximately 115 scientists, engineers, and support personnel.

Personal Research: Dr. Albritton joined the Aeronomy Laboratory in 1967 and conducted research on the laboratory investigation of atmospheric ion-molecule reactions and theoretical studies of diatomic molecular structure. In later years, his research interest has been the field investigation of atmospheric trace-gas photochemistry. He has published approximately 150 papers in these areas, has contributed numerous invited review papers, and has lectured worldwide on these subjects.

Research Planning: Dr. Albritton was one of two coordinators of the drafting of the initial research plan for the U.S. Global Change Research Program. He has been a member of review and steering groups for the National Academy of Sciences, other-Federal Agency and private-sector programs, and international research efforts such as the International Global Atmospheric Chemistry Program. He is the Science Vice-Chair of the Air Quality Research Subcommittee of the Committee on Environment and Natural Resources. He also leads the Atmospheric Chemistry Project of NOAA's Climate and Global Change Program and NOAA's "Health of the Atmosphere" regional air quality research program.

Scientific Assessments of the Stratospheric Ozone Layer: Dr. Albritton serves as Co-chair of the United Nations Environment Programme's Ozone Science Assessment Panel. In this capacity, he provides scientific information to the United Nations Montreal Protocol on Substances that Deplete the Ozone Layer. He has often been called upon to describe this science to other governmental and industrial organizations and to the public. He has also testified frequently before Congress on this topic.

Scientific Assessments of the Climate System: He has served as a Lead Author on the Intergovernmental Panel on Climate Change (IPCC) scientific assessment reports. He has been invited by numerous organizations to summarize the current scientific knowns and unknowns regarding the climate system.

Recognition and Awards: Dr. Albritton is a Fellow of the American Physical Society and of the American Geophysical Union. He has served on the Editorial Advisory Board of the Journal of Molecular Spectroscopy and the Journal of Atmospheric Chemistry, as well as serving as editor of the latter journal. Dr. Albritton has received several awards and honors for outstanding performance in NOAA, including two Department of Commerce Gold Medal Awards and two Presidential Rank Awards. For his role in leading scientific assessments of stratospheric ozone depletion, he has received a 1992 Special Award from the American Meteorological Society, the 1993 Scientific Freedom and Responsibility Award from the American Association for the Advancement of Science, the 1994 U.S. Environmental Protection Agency Stratospheric Ozone Protection Award, and a 1995 U. N. Environment Programme Ozone Award.


US CCSP  logo & link to home USGCRP logo & link to home
US Climate Change Science Program / US Global Change Research Program, Suite 250, 1717 Pennsylvania Ave, NW, Washington, DC 20006. Tel: +1 202 223 6262. Fax: +1 202 223 3065. Email: Web: Webmaster: