We need the sun: psychologically, because sunlight warms our hearts; physically, because our body needs it to produce vitamin D, essential to the healthy development of our bones. Yet increased doses of ultraviolet rays penetrating the ozone layer and reaching the surface of the Earth can do a lot of harm to plants, animals and humans.
Over thousands of years humans have adapted to varying intensities of sunlight by developing different skin colours. The twin role played by the skin – protection from excessive UV radiation and absorption of enough sunlight to trigger the production of vitamin D – means that people living in the lower latitudes, close to the Equator, with intense UV radiation, have developed darker skin to protect them from the damaging effects of UV radiation. In contrast, those living in the higher latitudes, closer to the poles, have developed fair skin to maximize vitamin D production.
Who is most at risk?
In the last few hundred years however, there has been rapid human migration out of the areas in which we evolved. Our skin colour is no longer necessarily suited to the environment in which we live. Fair skinned populations who have migrated to the tropics have suffered a rapid rise in the incidence of skin cancers.
Behavioural and cultural changes in the 20th century have meant that many of us are now exposed to more UV radiation than ever before. But it may also result in inadequate exposure to the sun which damages our health in other ways.
Many people from the higher latitudes grill their skin intensely in the sun during their short summer holidays, but only get minimal exposure to the sun for the rest of the year. Such intermittent exposure to sunlight seems to be a risk factor. On the other hand populations with darker skin pigmentation regularly exposed to similar or even higher UV rays are less prone to skin damage.
What damage is done?
The most widely recognised damage occurs to the skin. The direct effects are sun burn, chronic skin damage (photoaging) and an increased risk of developing various types of skin cancer. Models predict that a 10 per cent decrease in the ozone in the stratosphere could cause an additional 300,000 non-melanoma and 4,500 (more dangerous) melanoma skin cancers worldwide annually.
At an indirect level UV-B radiation damages certain cells that act as a shield protecting us from intruding carriers of disease. In other words it weakens our immune system. For people whose immune system has already been weakened, in particular by HIV-Aids, the effect is aggravated, with more acute infections and a higher risk of dormant viruses (such as cold sores) erupting again.
UV radiation penetrates furthest into our bodies through our eyes, which are particularly vulnerable. Conditions such as snow blindness and cataracts, which blur the lens and lead to blindness, may cause long-term damage to our eyesight. Every year some 16 million people in the world suffer from blindness due to a loss of transparency in the lens. The World Health Organisation (WHO) estimates that up to 20 per cent of cataracts may be caused by overexposure to UV radiation and could therefore be avoided. The risk of UV radiation-related damage to the eye and immune system is independent of skin type.
|#4a. Could break the issue down to look at specific health issues, e.g., eyes.
#4b. Could potentially break the issue down regionally and look at health threats from ozone from an environmental justice perspective in, say, Africa. Africa produces no ODSs, consumes few and bears disproportionate health risks as a high percentage of its populations are trying to cope with HIV.
#4c. Are some races or ethnicities particularly vulnerable? Potentially interesting, if there is recent and underreported science in this area.
No reason for reduced attention
Simple counter-measures (see chapter 9) can control the direct negative effects of UV radiation on our health. But that is no reason to reduce our efforts to reverse destruction of the ozone layer. It is difficult to foresee the indirect effects such profound changes in the atmosphere may have on our living conditions. Changes to plants or animals might affect mankind through the food chain, and the influence of ozone depleting substances on climate change might indirectly affect our ability to secure food production.