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 culprit is thought to be CFC (Chloroflourocarbon) 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. 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, The field has come of age, and the large majority of scientific community support that the ozone hole is at least partially due to human fault.