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Climate Change and Human Health

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The projected large increases in damaging ultraviolet radiation as a result of global emissions of ozone-depleting substances have been forestalled by the success of the Montreal Protocol. In 1987, an international treaty called the Montreal Protocol was signed to phase out all CFC usage.

The three most common types of skin cancer are basal cell carcinoma (BCC), squamous cell carcinoma (SCC) and malignant melanoma (MM). Exposure to ultraviolet radiation is recognized as a risk factor in all three malignancies. Approximately 90% of skin cancers are non-melanocytic, the vast majority of these are BCCs.

BCCs are commonly known as rodent ulcers; they usually arise in sun-exposed areas of the body and have a propensity to cause extensive local tissue damage. Patients with these malignancies are usually fair-skinned and tend to burn rather than tan in sunlight. An Italian study has also highlighted a definite association between BCC development and recreational sun exposure during childhood and adolescence. The exact nature of the wavelengths and exposure patterns involved in BCC carcinogenesis is still equivocal to a large degree, however recent studies demonstrate a correlation between ultraviolet B radiation (UV-B, 290–320 nm) and BCC risk.

SCCs account for a significant proportion of non-melanocytic skin cancer. SCCs are caused by sunlight-induced mutations in the p53 tumour suppressor gene. They are found almost exclusively on sun-exposed skin such as the neck, face and arms, and the incidence is linked with geographical location, being higher at latitudesreceiving more sun such as Australia.

Malignant melanoma is the most serious form of skin cancer: it is responsible for around 80% of skin cancer deaths. Over the last 25 years the reported incidence of malignant melanoma has increased. This is likely to be due to increased UV exposure, however the number of skin biopsies now taking place has also risen. An American study revealed that an increase in skin biopsy rates corresponded to an increase in the incidence of local melanoma while mortality rates remained unchanged, the authors have attributed the rising incidence of melanoma to an increase in diagnostic scrutiny rather than an actual increase in the incidence of disease. Melanoma is also the third most common cancer among 15–39 year olds. Exposure to UVR, fair skin, dysplastic naevi syndrome and a family history of melanoma are major risk factors for melanoma development. UV-B appears more closely associated with the development of melanoma than UV-A (320–400 nm). This is supported by the higher incidence of melanoma in equatorial regions than in latitudes further from the equator, as UV-B radiation is most intense at the equator while UV-A intensity varies less across latitudes. Although UV-B appears to be more important than UV-A as a risk factor, a causal link to UV-A exposure is also supported by data from patients using tanning beds and or treated with psoralan UV-A (PUVA) for psoriasis.

New challenges are now arising in relation to climate change. Many epidemiological studies have implicated solar radiation as a cause of skin cancer (melanoma and other types). Recent assessments by the United Nations Environment Program project increases in skin cancer incidence and sunburn severity due to stratospheric ozone depletion for at least the first half of the twenty-first century (and subject to changes in individual behaviours).

Culturally-based behavioural changes have led to much higher UV exposure, through sun-bathing and skin-tanning. The marked increase in skin cancers in western populations over recent decades reflects, predominantly, the combination of background, post-migration, geographical vulnerability and modern behaviours.

Scientists expect the combined effect of recent stratospheric ozone depletion and its continuation over the next 1-2 decades to be (via the cumulation of additional UVB exposure), an increase in skin cancer incidence in fair-skinned populations living at mid to high latitudes. The modelling of future ozone levels and UVR exposures study has estimated that, in consequence, a ‘European’ population living at around 45 degrees North will experience, by 2050, an approximate 5% excess of total skin cancer incidence (assuming, conservatively, no change in age distribution). The equivalent estimation for the US population is for a 10% increase in skin cancer incidence by around 2050.

Ozone depletion has lead to an increase in skin cancers and worryingly this is still rising. The depletion will however peak and then the ozone layer will begin to repair itself. Focus must now shift towards analysing the social and behavioural changes that will come about through climate change. Warmer, drier weather in the is likely to encourage people to spend more time outdoors and increase their exposure to UVR. The consequence will be an increase in the incidence of skin cancer brought about by behavioural change rather than environmental change. The world has had 30 years of public health initiatives and awareness campaigns. These must be heeded and acted upon now to protect the public from this preventable threat.

The bright spot? All types of skin cancer are 100 percent curable, if recognized and treated early. In 2011, the Journal of Clinical Oncology published a randomized, clinical study of over 1,600 people showing that regular sunscreen use reduced the incidence of melanoma by 50-73%. When used as directed with other sun protection measures, broad spectrum sunscreen higher helps prevent sunburn and reduces the risk of early skin aging and skin cancer (melanoma and squamous cell carcinomas) associated with UV radiation. 

Additionally, several scientific research studies disprove claims that sunscreen use increases melanoma risk. These comprehensive assessments of thousands of people found that sunscreen use does not, in fact, increase one’s risk of developing melanoma.

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