The 2010 United Nations Environment Program (UNEP) assessment of the environmental effects of ozone depletion and its interactions with climate change concluded that projected changes in ozone and clouds may affect levels of ultraviolet (UV) radiation at the Earth’s surface (though the effects vary according to geographical location). Although the impact on skin cancer risk has not been a major focus of climate change research, changing levels of UV radiation and warming temperatures may affect skin cancer incidence.
Australia has warmed on average by 1.44 ± 0.24 °C since national records began in 1910, with most warming occurring since 1950 and every decade since then being warmer than the ones before Warmer temperatures may result in Australians increasing their sun exposure and wearing less covering clothing, thereby increasing their risk of skin cancer. However, very high temperatures may instead prompt behaviours to avoid sun exposure, and therefore "there is considerable uncertainty in modeling future human behaviour in response to climate change". There is weak animal model evidence that higher ambient temperatures may increase the skin cancer-effective UV dose by a few percent per celsius, which would result in more skin cancers for the same level of UV radiation. However, this is highly speculative.
The stratospheric ozone layer serves as a critical UVR filter, effectively shielding the earth from ultraviolet C and a large portion of ultraviolet B. The increase in UVB levels due to stratospheric ozone depletion that has occurred may have contributed to the increasing skin cancer incidence rates in Australia since the 1970s. However, other factors, such as sun-seeking behaviour during the second half of the 20th century and an ageing population are also important. We do not know which of these has been most important or how much each contributes to the higher skin cancer incidence since the 1970s.
The Montreal Protocol protects the stratospheric ozone layer and has reduced the damaging health effects of excessive exposure to solar UV radiation. Complete compliance with the Montreal Protocol is estimated to prevent two million skin cancer cases worldwide by 2030.
In Australia, small increases in UVB radiation of up to 5% were observed between 1980 and 2010. However, with implementation of the Montreal Protocol ozone recovery is expected. Ozone levels are expected to return to 1980s levels by mid-century in Australian states in the middle latitudes (all capital cities except Darwin). However, UV radiation levels are dependent on a variety of factors in addition to ozone levels and are sensitive to future changes in cloud cover and air pollutant/aerosol concentrations. These latter factors will be the most important modifiers of UV radiation on the Earth’s surface, in the future.
Assuming time-invariant amounts of aerosol, the clear-sky UVI is projected to decrease from 2015 to 2090 by 6% at southern mid-latitudes such as the southern regions of Australia. However, in regions that are affected by air pollution, increases will occur where emissions of air pollutants are curtailed in the future. For example, in Mexico City the UV index increased by 25% between 2000 and 2019 due to reductions in pollutants.
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