Question: What is depletion of the ozone layer caused by?
About the article "Global warming", section "Solar activity".

Candidate passages:
While the effect of the Antarctic ozone hole in decreasing the global ozone is relatively small, estimated at about 5% per decade, the hole has generated a great deal of interest because:  The decrease in the ozone layer was predicted in the early 1980s to be roughly 7% over a 60-year period.
The sudden recognition in 1985 that there was a substantial "hole" was widely reported in the press.
The especially rapid ozone depletion in Antarctica had previously been dismissed as a measurement error.
Many of those unsure about what the ozone hole was and what caused it were worried that ozone holes might start appearing over other areas of the globe, but to date the only other large-scale depletion is a smaller ozone "dimple" observed during the Arctic spring over the North Pole.
Ozone at middle latitudes has declined, but by a much smaller extent (about 4–5% decrease).
If the conditions become more severe (cooler stratospheric temperatures, more stratospheric clouds, more active chlorine), global ozone may decrease at a much greater pace.
Standard global warming theory predicts that the stratosphere will cool.
When the Antarctic ozone hole breaks up, the ozone-depleted air drifts out into nearby areas.
Decreases in the ozone level of up to 10% have been reported in New Zealand in the month following the breakup of the Antarctic ozone hole, with ultraviolet-B radiation intensities increasing by more than 15% since the 1970s.  
A team of scientists are studying ozone depletion while living in a lab in the Amazon Rainforest when they are attacked by a clinical lycanthrope who has gone insane because of over-exposure to the sun's ultraviolet rays, caused by the hole in the ozone layer. 
The Scientific Assessment of Ozone Depletion is a sequence of reports sponsored by WMO/UNEP.
The most recent is the 2010 report.
The reports were set up to inform the Montreal Protocol and amendments about ozone depletion.  
Since the ozone layer absorbs UVB ultraviolet light from the sun, ozone layer depletion is expected to increase surface UVB levels, which could lead to damage, including increase in skin cancer.
This was the reason for the Montreal Protocol.
Although decreases in stratospheric ozone are well-tied to CFCs and there are good theoretical reasons to believe that decreases in ozone will lead to increases in surface UVB, there is no direct observational evidence linking ozone depletion to higher incidence of skin cancer and eye damage in human beings.
This is partly because UVA, which has also been implicated in some forms of skin cancer, is not absorbed by ozone, and it is nearly impossible to control statistics for lifestyle changes in the populace. 
The ozone hole is an annual thinning of the ozone layer over Antarctica, caused by stratospheric chlorine.
Other more moderate thinnings have also been called "ozone holes", such as that over the North Pole during certain weather conditions.
The discovery of the annual depletion of ozone above the Antarctic was first announced in a paper by Joe Farman, Brian Gardiner and Jonathan Shanklin which appeared in "Nature" in May 1985.
The most pronounced decrease in ozone has been in the lower stratosphere.
However, the ozone hole is most usually measured not in terms of ozone concentrations at these levels (which are typically of a few parts per million) but by reduction in the total "column ozone", above a point on the earth's surface, which is normally expressed in Dobson units.
Marked decreases in column ozone in the Antarctic spring and early summer compared to the early 1970s and before have been observed using instruments such as the Total Ozone Mapping Spectrometer (TOMS).
In 2012, it has been reported that the ozone hole had decreased to the smallest size since 2002.