The international community started to take action to prevent further large-scale depletion of stratospheric ozone with the [Vienna Convention for the Protection of the Ozone Layer], 1985. In 1987 countries agreed on the [Montreal Protocol on Substances that Deplete the Ozone Layer], under which world consumption of specified chlorfluorocarbons (CFCs) and halons would be frozen and total CFC consumption would be reduced by 50% by the year 2000, relative to the base year 1986. Since then four amendments (London, Copenhagen, Vienna and Montreal) have been made to the original Protocol.
Nasa scientists have used improved understanding of weather systems and of the higher layers of the Earth's atmosphere to produce new models of ozone depletion. Paradoxically, global warming is one of the key culprits causing the cooling. As greenhouse gases accumulate in the lower atmosphere, they absorb heat radiated from the Earth that would otherwise escape into the upper atmosphere, warming it up. Man-made chemicals, including CFCs, the production of which the developed world is now repressing, take 10 to 15 years to work their way upwards. In cooler temperatures, they are much more damaging to ozone.