Stratospheric ozone depletion

Stratospheric ozone protects life on Earth from ultraviolet radiation from the sun. The stratospheric ozone concentration has been depleted at a rate of about 4 % a decade since the late1970s. A much larger, but seasonal, depletion takes place each year over the polar regions. These are the so called ozone holes. Ozone depletion is caused by emissions of halogenated carbon compounds such as chlorofluorocarbons (freons) and bromofluorocarbons (halons). Thanks to the Montreal Protocol (see that was signed in 1987 and which regulates the use and emissions of ozone depleting substances, the trend is now a decrease in these substances since the peak values in 1992-1994. This is probably the best example of positive effects from determined human efforts to avoid environmental threat.