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WMO and UNEP issue summary of scientific assessment of the ozone layer 1998

Nairobi/Geneva, 22 June 1998 - The World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) have jointly released today the Executive Summary of the "Scientific Assessment of Ozone Depletion - 1998". It has been prepared by more than 200 scientists from around the world and was reviewed from 1 to 6 June by 77 scientists from 27 countries.

The Executive Summary confirms the effectiveness of the Montreal Protocol on Substances that Deplete the Ozone Layer, which has proved to be an outstanding success so far. A full recovery of the Earth's protective ozone shield could occur by the middle of next century, but it would require that the Protocol is fully implemented.

The heads of both United Nations bodies expressed their thanks to the scientists working on the Assessments. "Over the past two decades, the scientists have provided excellent and unbiased advice to the Governments and showed them the effective path to save the ozone layer. The world owes them a debt of gratitude," said Mr Klaus Toepfer, Executive Director of UNEP.

While welcoming the report's findings, Mr Toepfer cautioned against complacency and urged all Parties to the Protocol to seize every opportunity to reduce their emissions of ozone-depleting chemicals. "The use of economic instruments has played an important role in the phase-out achieved so far by the industrialized countries," said Mr Toepfer. "The developing countries, due to begin the phase-out next year, can speed up the process by using these instruments, in addition to faster implementation of projects sanctioned by the Montreal Multilateral Fund, so far at a cost of US$740 million," he said.

Prof. Obasi, Secretary-General of WMO, paid tribute to the continuous efforts of WMO Member countries which have been carrying out systematic observations and analysis of ozone and related chemical compounds for the last four decades. Without such data and scientific assessments it would have been impossible to detect the start of the ozone decline in the 1970s," he said. In fact, remedial actions that were later taken as a result of the Montreal Protocol were made possible thanks to these efforts.

"The WMO global network of stations is detecting lower rates of increase in bromine and a decline of chlorine concentrations from ozone-destructive substances in the troposphere, obviously as a result of the restrictions made by the Montreal Protocol. However, perhaps it might not be possible to detect firm signs of ozone recovery before another 20 years, due to the natural atmospheric and ozone variability," said the Secretary-General. He further urged Governments to continue to expand their activities in atmospheric monitoring and research, including those on tropospheric ozone which is becoming an essential component in the understanding of the ozone- climate issue.

Among the recent major scientific findings and observations mentioned in the Executive Summary of the Ozone Assessment 1998 are:


  • The combined total abundance of ozone-depleting compounds in the troposphere (the lowest part of the atmosphere) peaked in 1994 and is now slowly declining. However, total concentrations of bromine are still increasing;
  • In the northern polar latitudes, in six out of the last nine boreal winter-spring seasons, ozone has declined during some months by 25 % to 30 % below the 1960s average;
  • In the Antarctic, the appearance of the ozone hole during the austral springs has continued unabated, with ozone column losses usually exceeding 50 % during the months of September and October;
  • Only over the middle latitudes in both the northern and southern hemispheres has the ozone decline slowed in comparison with the previous scientific assessment in 1994;
  • If measures had not been taken in accordance with the Montreal Protocol and its Amendments and Adjustments, the ozone decline would have been much stronger and would have continued for many more decades;
  • 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 centigrade per decade since 1979);
  • The increase of ozone in the troposphere since pre-industrial times is estimated to have contributed 10 % to 20 % of the warming due to the increase in long-lived greenhouse gases during the same period;
  • The abundance of ozone-depleting substances in the stratosphere is expected to peak by the year 2000. However, when changing atmospheric conditions are combined with natural ozone variability, detecting the start of the ozone layer recovery may not be possible for perhaps another 20 years.

Even though the Protocol is working well to reduce the use and release of ozone-depleting substances, the life of chemicals already released in the atmosphere will keep the depletion going for years to come.

The ozone layer in the stratosphere (about 12-45 km above the ground) shields the Earth's surface from the Sun's damaging ultraviolet (UV-B) rays. Exposure to increased UV-B radiation at the Earth's surface is known to result in skin cancer, and unpredictable damage to plants, algae, the food chain and the global ecosystem. WMO and UNEP have been working in close cooperation with leading scientists for many years to provide the scientific evidence on the continued threat of ozone layer depletion. A thorough review of the state of the ozone layer was discussed at a meeting organized by both organizations in Les Diablerets, Switzerland, from 1 to 6 June 1998. The last international assessment was published in 1994.

The full Scientific Assessment 1998 on the state of the ozone layer will be published in its entirety by WMO and UNEP late this year and will be available as WMO Ozone Report No. 44.

For more information, please contact:

Ms. Eirah Gorre-Dale,
WMO Information and Public Affairs Office in Geneva
on tel: +41-22-730-8315, fax: 733-2829,


Robert G. Bisset
Media and Communications Officer
UNEP, P.O. Box 30552, Nairobi, Kenya
Tel. +254-2-623084, Fax. +254-2-623692,

UNEP News Release 1998/64

Monday 22 Jun 1998
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