A thinning in the ozone layer was first measured in 1976. In the mid 1980’s the cause of this ‘hole’ was identified as CFC gasses. In 1986, 70 countries signed the Montreal Protocol, agreeing to stop the use of CFC’s. Since the 1990’s the ozone layer has been gradually recovering, though it won’t be until 2100 that in will reach 1970 levels. (http://bit.ly/2ODgkao)