Oxygen in the stratosphere (10–50 km up) encounters ionizing radiation. The O2 breaks up, recouping itself into a molecular mass of O3: ozone.
The stratospheric ozone layer (20–40 km) has a mere 10 parts per million (ppm) of O3, compared to 0.3 ppm in the air below, but that margin in the ozonosphere is crucial to rendering the planet habitable.
The ozone layer absorbs ~98% of the Sun’s medium-frequency ultraviolet light (200–315 nm wavelength); UV radiation which otherwise would be hazardous to life on the surface, such as engendering cancer in humans.
A thinner ozonosphere facilitates global warming by letting in more sunlight, but ozone layer depletion does not affect the absorption of heat in the atmosphere.
The ozonosphere does have an indirect effect on global climate. A hole in Antarctic ozone layer caused by man-made aerosol pollution changed the way that waters mixed in the Southern Ocean.
Formation of the Antarctic ozone hole has caused large-scale coherent changes in the ventilation of the southern oceans. Southern oceans play an important role in the uptake of heat and carbon dioxide, so any changes in Southern Ocean circulation have the potential to change the global climate. ~ American climatologist Darryn Waugh