The phenomena which shows a steady decline in the total volume of ozone in the Earth’s protective stratosphere or ozone layer, which filters the sun’s harmful UVB rays. This steady decline in volume has been observed to have started in the late 1970’s. Another type of ozone depletion phenomena is the ozone hole which is a larger, but seasonal decrease in stratospheric ozone over the polar regions. Scientists believe that ozone depletion has contributed to higher rates of skin cancer, cataracts, plant damage and reduction of plankton in the sea.