Stratospheric Ozone Depletion - The Changing Arctic Environment: The Arctic Messenger - page 114

patterns of skin cancer occurrence on the body that relate to cumulative UV exposure and
lifestyle. For example, head and neck tumours are common in elderly people. In younger
people, the highest rates of cutaneous malignant carcinoma occur on the trunk for males
and on the limbs for females.
In the Arctic, skin cancer rates have generally been low, presumably due to a combin-
ationoftheprotectiveskinpigmentationofindigenouspeoples,thelowaverageUVexpos-
ure and the heavy clothing usually worn. However, the 2005 ACIA report quoted studies
showing that females of Danish descent in Greenland have been showing a higher inciden-
ce of melanoma and nonmelanoma cancers.
It is not surprising to learn that our eyes are vulnerable to UV radiation. There is now
strong epidemiological and experimental evidence for an association between exposure to
UV-B and the incidence of age-related cortical cataracts. There is also some evidence of as-
sociation with other forms of cataract and for a condition called pterygium . Here, however,
the case is less strong. Pterygium is an inflammatory invasive growth on the conjunctiva
and cornea that can impair vision.
Suppression of the immune system is the last impact of UV exposure on humans that
we will look at briefly. Many animal studies have shown that during an infection, there are
critical stages when UV-B exposure can increase the severity of symptoms and duration
of the disease. For example, solar UV radiation can trigger the reactivation of the latent
herpes simplex virus. This effect has some very practical generic implications for health
care because it is now known that UV exposure before (and possibly immediately after) in-
oculation can reduce the strength of the immune response. Consequently, the effectiveness
of the vaccination can also be reduced.
Therecoveryoftheozonelayerisexpected toleadtoanoverallreductioninthelevels
of UV radiation arriving at Earth's surface. Compared to 1980, UV-B irradiance towards
the end of the twenty-first century is tentatively projected to be lower at mid- to high latit-
udes by between 5% and 20%, respectively, and higher by 2-3% in the low latitudes. The
expectation of lower levels at mid-latitudes reflects the impact of climate warming we have
just reviewed. If we do indeed find ourselves in a situation of 20% less UV-B irradiance