An ozone hole is a local weakening in the ozone layer of the atmosphere. In recent times, ozone holes have been observed to form over Arctica and Antarctica during certain weather conditions.
The ozone hole over Antactica have in some instances grown so large as to affect southern parts of Australia and New Zealand, and cause a significant increase in ultraviolet radiation reaching the surface of the planet. This is because ozone, O3, absorbs this type of radiation. As it is being destroyed more radiation reaches the earth. In a seeming contradiction, it is this same UV radiation that creates the ozone in the ozone layer from O2 (regular oxygen) in the first place.
The cause of the ozone holes are subject to much scientific debate but the leading cause is thought to be CFC (Chlorofluorocarbon) compounds which breaks down (due to UV light) and become free radicals high in the Earth's atmosphere. These radicals then break down the ozone.
CFCs are a byproduct of some chemical processes, and were also used in air conditioning/cooling units. They were also used as an aerosol propellants. What makes CFCs so effective in breaking down ozone is that one CFC radical acts as a catalyst and can break down many ozone molecules. Also these radicals stay in the atmosphere for a very long time. This is the reason that the increased radiation does not adequately affect the creation of more ozone--the CFCs don't go away.
Environmentalists assert that the CFCs have caused so much damage to the ozone layer that the use of CFCs should be banned. The amount of this damage CFCs have caused is not known, however, and the full extent of the damage caused by them will not be known for decades.
Initial study of the causes of the ozone hole, while in retrospect appear to have drawn the correct conclusions, were nonetheless not the most unbiased or valid. For example, much publicity was made of satellite data showing massive depletion of ozone around the south pole before it was discovered that the satellite programming was faulty, resulting in skewed results.
Anecdotal evidence of effects of ultraviolet radiation on indigenous animals proved unverifiable. However, recent research [1] has analyzed a widespread extinction of plankton 2 million years ago that coincided with a nearby supernova. Researchers speculate that the extinction was caused by a significant weakening of the ozone layer at that time when the radiation from the supernova produced nitrogen oxides that catalyzed the destruction of ozone (plankton are particularly susceptible to effects of UV light, and are vitally important to marine food-webs).
The large majority of scientific community support that the ozone hole is at least partially due to human fault. However, to what degree humans are at fault is still uncertain, as is how much damage the ozone hole will do to the environment or to human beings. Despite environmentalist claims linking CFCs to ozone depletion and skin cancer, no studies have found evidence of such a link.
See: Montreal Protocol
External references:
- Stratospheric Ozone Depletion at NOAA website
- The Ozone Tour] at the Centre for Atmospheric Sciene, University of Cambridge