Ozone recovery will be long-term affair

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Although the full recovery of the Earth's ozone shield is expected to occur by the middle of the next century, signs of the recovery may not become apparent for another two decades. That is the conclusion of the latest four-yearly ozone assessment published this week by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP).

Still growing: the ozone hole is as big as ever in this view of the South Pole in October 1997. Credit: AP/NOAA

Godwin Obasi, secretary-general of the WMO, said the report, prepared by more than 200 scientists from around the world, showed that the 1987 Montreal protocol to phase out ozone-depleting substances is clearly working.

“The WMO global network of stations is detecting lower rates of increase in bromine and a decline in chlorine concentrations in the troposphere,” Obasi said. But he added: “It might not be possible to detect firm signs of ozone recovery before another 20 years due to natural atmospheric and ozone variability.”

Klaus Töpfer, executive director of UNEP, said the world owed scientists “a debt of gratitude” for their “unbiased advice”, and for showing governments an “effective path to save the ozone layer”. But he added that a complete recovery of ozone levels will need complete compliance with the protocol, particularly from developing countries.

Under the terms of the Montreal protocol, these countries must complete the phasing out of ozone-depleting chemicals by 2005. They are due to start next year. But emissions from India and China have exceeded earlier projections.

Developing countries have access to a global fund — the Montreal Multilateral Fund — to help them make the transition to using and producing alternatives to ozone-depleting chemicals.

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Masood, E. Ozone recovery will be long-term affair. Nature 393, 723 (1998). https://doi.org/10.1038/31554

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