In the May, 1985 issue of the journal "Nature," the British Antarctic Survey Team that originally discovered the Ozone Hole published conclusive evidence of ozone depletion. The new evidence prompted a reexamination of the older U.S. satellite data which had previously been disregarded. Both sets of data were found to be in agreement. The implications of the new evidence made the guidelines agreed upon at the Vienna Convention obsolete, and prompted the formulation and release of the Montreal Protocol on Substances that Deplete the Ozone Layer in 1987.
Many nations had concerns. The U.S. wanted to ensure compliance in terms of trade restrictions, the Soviet Union wanted to use two CFC-production plants that were under construction, and Japan wanted an Ozone Destruction index, so it could continue to use CFC-113, which is a smaller threat to ozone-depleting than other CFCs.
In the end, developed countries agreed to phase out CFCs by the year 2000. HCFCs, which harm ozone to a much lesser degree than CFCs, were considered transitional substitutes that would be phased out by 2030. These substances are used in large industrial coolers that have a lifetime of 40 years. It would be a great expense to replace them.
Technical progress was very rapid, and several adjustments were made to the protocol. The latest adjustments totally banned most CFCs, halons, and methyl chloroform by 1996. HCFCs have until 2030, and methyl bromide, until 2010.
Already, a decrease in CFC concentrations has been noted in the troposphere, but it will be years before improvement is seen in the stratosphere.
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