The shrinking ozone holes
11 February 2013
Antarctic ozone hole: 2011 and 2012
Since the beginning of the 1980s, gigantic holes have formed each year in the ozone layer, high above Earth’s polar regions. Satellites such as ESA’s ERS-2 and Envisat have shown how these holes have developed and grown, sometimes covering an area as large as Europe.
However, ozone concentrations are rising, and it seems that the hole over Antarctica may slowly be disappearing. The even better news is that the ozone sensor on Europe’s MetOp weather satellite found that, in 2012, the hole over Antarctica shrank to its smallest size in 10 years!
Ozone is a form of oxygen. Small amounts of ozone gas are found in the stratosphere, 20 - 50 km above the Earth. Fortunately for us, the layer of ozone protects us from the Sun’s ultraviolet light, a major cause of skin cancer.
The evolution of the ozone layer is affected by a mixture of atmospheric chemistry, wind and temperature. Unusual weather and atmospheric conditions can result in extreme ozone conditions, such as the record low observed above the Arctic in spring 2011.
However, human pollution is the major cause of ozone loss. Chemical reactions involving chlorine compounds (CFCs) in high level clouds destroy the ozone. As the polar spring arrives, the combination of returning sunlight and chlorine chemistry causes ozone molecules to split into oxygen. A single molecule of chlorine can break down thousands of molecules of ozone.
Although CFCs were banned in 1987, they survive for many years in the atmosphere. It may take until around 2050 for the chlorine levels to return to the low values of the 1960s. Until then, satellites will continue to study the seasonal changes in the ozone layer.