Ozone depletion

The stratosphere is the upper of the two atmospheric layers closest to Earth (the troposphere being the lower one), and it hosts what is called the 'good' ozone layer, distinct from the ground-level 'bad' ozone found in the troposphere. This stratospheric ozone shield absorbs the bulk of the sun's ultraviolet radiation, particularly the more damaging UV-B and UV-A wavelengths, before it can reach living organisms at the surface; UV-C, the most damaging wavelength band, is fully filtered out by the atmosphere regardless. Ozone thickness is expressed in Dobson Units (DU) — one DU corresponds to a layer of pure ozone 0.01 mm thick at standard temperature and pressure — and Earth's average total ozone column works out to roughly 300 DU (about 3 mm). Man-made chlorofluorocarbons, widely used historically in refrigeration, aerosol propellants and industrial cleaning, chemically break down stratospheric ozone molecules; when this thinning becomes severe over a specific region it is termed an ozone hole. International recognition of the threat led to the Vienna Convention (agreed 1985, in force 1988), which laid the diplomatic groundwork for the binding Montreal Protocol (1987), committing signatory nations to phase out ozone-depleting substances. The later Kyoto Protocol's Clean Development Mechanism (CDM, 2007) extended this cooperative framework to broader greenhouse-gas reduction, letting projects such as replacing conventional power generation with solar installations earn tradeable Certified Emission Reduction credits. Certain plant species also s …