Air pollution
A global concern is the hole in the ozone layer in the stratosphere.  The Earth's ozone layer protects life from the Sun's harmful ultraviolet rays, but in the 1970s, scientists found out that some chemicals let out into the atmosphere makes the ozone turn into oxygen.  This lets more ultraviolet rays reach the Earth.  During the 1980s, scientists found that the ozone layer above the South Pole had thinned by 50 to 98%.