Scientific assessment of ozone depletion

Scientific Assessment of Ozone Depletion is a sequence of reports sponsored by WMO/UNEP. The most recent is the .

The reports were set up to inform the Montreal Protocol and amendments about ozone depletion.

Findings

In the troposphere observations show that the total abundance of ozone-depleting compounds continues to decline slowly from the peak that occurred in 1992-1994.
Observations in the stratosphere indicate that the total chlorine abundance is at or near a peak, while bromine abundances are probably still increasing.
Analyses of air trapped in snow since the late 19th century have confirmed that non-industrial sources of the CFCs, halons, and major chlorocarbons were insignificant.
The abundances of HCFCs in the troposphere continue to increase.

Springtime Antarctic ozone depletion due to halogens has been large (40-50%; exceptionally 70%) throughout the last decade.
In some recent cold Arctic winters during the last decade, maximum total column ozone losses due to halogens have reached 30%, but in warmer winters Arctic ozone loss is small.
Ozone remains depleted in the midlatitudes of both hemispheres. The global-average total column ozone amount for the period 1997-2001 was approximately 3% below the pre-1980 average values.
Models capture the observed long-term ozone changes in northern and southern midlatitudes.

Chemistry-climate models predict that springtime Antarctic ozone levels will be increasing by 2010 because of projected decreases of halogens in the stratosphere. A return to pre-1980 total column ozone amounts in the Antarctic is expected by the middle of this century.
Arctic ozone depletion is highly variable and difficult to predict, but a future Arctic polar ozone hole similar to that of the Antarctic appears unlikely.

Decreases in ozone amounts lead to increases in UV radiation. Calculations of UV irradiance based on relationships with total ozone and total irradiance suggest that UV irradiance has increased since the early 1980s by 6-14% at more than 10 sites distributed over mid- and high latitudes of both hemispheres. But complexities (e.g. clouds, aerosol, snow cover, sea ice cover, and total ozone) limit the ability to describe fully surface ultraviolet radiation on the global scale. Surface ultraviolet data records, which started in the early 1990s, are still too short and too variable to permit the calculation of statistically significant long-term (i.e., multidecadal) trends.

(The bracketed 1988, 1985 and 1981 papers are precursor reports relevant to the Montreal Protocol but not directly part of this series).


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