Despite scientific concerns in the 1960s and 1970s at the possibility of damage to the stratospheric ozone layer from exhaust emissions from fleet of supersonic aircraft, it was only after the discovery of the so-called ozone 'hole'- a decrease in the concentration of ozone in the Antarctic stratosphere in spring - that a strong causal link was established between the release of chlorofluorocarbons ( or CFC - artificial gases used in refrigeration, spray cans and for other purposes) and the destruction of ozone in the presence of ice particles in the very cold Antarctic stratosphere