GLOBAL levels ofozone, which shields the from the Sun's harmful ultraviolet radiations, have fallen to a record over the past 2 years. But the worst R to come, according to the report of an international scientific panel. However, a redeeming feature of the 1994 Assessment Panel report, mandated under the 1987 Montreal Protocol on Substances that Deplete the Ozone Layer, is that the emissions of chemicals harmful to ozone have also gone down.
The 'panel was set up under the auspices, of the Geneva-based World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) in Nairobi. It comprised 226 atmospheric science experts, drawn from 29 countries.
The report reveals that the atmospheric growth rates of human-made compounds that deplete the ozone layer, such as chlorofluorocarbons (CFCs), used in refrigeration, and halons, used in fire extinguish ers, have slowed in recent years following reductions in global emissions of these compounds. Says UNEP executive director Elizabeth Dowdeswell, "While the 1994 Assessment Panel report confirms that we are heading in the right direc tion, we cannot afford to be complacent. The line that divides complacency from cata strophe is very thin and now is not the time to break that momentum."
The report lists 4 steps that will steepen the fall from the peak halocarbon levels in the early decades of the next century. reductions in emissions of methyl bromide used as a soil and crop fumigant, reductions in emissions of hydrochlorofluorocarbons, the complete recapture (as opposed to recycling) Of CFcs, and halons banked in existing equipment.
Maximum loss During the winters of 1992 and 1993, the Antarctic ozone "hole" became bigger and deeper. Satellites and balloon-borne and groundbased monitoring instru- ments revealed that ozone over the Antarctic was depleted by -more than 99 per cent between the heights of 14 to 19 krn in October 1992 and 1993. Over the same period, ozone levels over populated regions of the northern hemisphere also Regis tered a record low. The loss was 10 per cent in 1992 and 7 per cent in 1993 over the ozone levels in the late '60s, according to G L Manney of the California Institute of Technology and his colleagues (Nature, Vol 370, No 6489).
The panel report contends that this record depletion probably owed, at least in part, to chemical processes linked to the 1991 eruption of Mount Pinatubo in the Philippines.
Scientists reckon that peak global ozone depletions would occur around 1998, mainly because of the past emissions. Thereafter, the levels of ozonedepleting chlorine and bromine are expected to slowly decrease and the ozone layer is expected to recover in about 50 years.
Nelson I Sabogal, an officer at, UNEWS Ozone Secretarias Nairobi, says that extrap olation of the rent trends 'suggests that ozone loss relative to the late '60s about 13 per cent at northern mid tudes in winter and spring - abow per cent above the current de levels. And it is estimated that im southern latitudes the ozone loss 11 per cent of the level in the late '60s.
According to UNEP, large inc uv radiation on the earth's surface been observej in the Antarctic and southern part of South America spring and winter, when the ozone is observed. Further, elevated Liat the mid to high latitudes observed in the northern hemi 1992 and 1993, corresponding low ozone levels in those yeam increase in ov radiation, experts could lead to an increase in skin cases and cataracts, especialiv people residing in the mid-latitudes.