Ultraviolet (UV) radiation’s effects on human health under the changing climate

UV radiation

Click in the image to access the four-day UV Index forecast by the Copernicus Atmosphere Monitoring Service

Health issues

Sunburn (i.e. skin reddening; or solar erythema) and tanning are the best-known human health effects of excessive ultraviolet (UV) exposure (DWD, 2015). Chronic exposure to UV radiation can cause degenerative changes in the cells, fibrous tissues and blood vessels, which over the course of a lifetime can lead to non-melanoma skin cancer. Periodic exposure to high doses of UV causing sunburn, in particular in childhood, is linked to (malignant) melanoma (more serious type of skin cancer, one of the causes of death from cancer) (DWD, 2015), especially among those with skin types prone to burning (IARC, n.d.).

Prolonged exposure to UV radiation plays a role in the development of cataracts and other eye diseases responsible for a large proportion of visual impairment world-wide. Abnormal skin reactions due to light-sensitivity, such as photodermatoses and phototoxic reactions to drugs can also occur (Lucas et al., 2019).

However, small amounts of UV radiation are essential in vitamin D synthesis required for bone health (SERC, n.d.) and immune function with benefits for skin diseases such as psoriasis (Lucas et al., 2019). Therefore, moderate exposure to sunlight is beneficial for health, especially in higher geographical latitudes. The WHO et al. (2002) “Global solar UV Index – A Practical Guide” summarises the health effects of exposure to UV radiation.

Observed effects

Incidence of malignant melanoma in fair-skinned populations has risen in the last decades, largely in association with personal habits in relation to sun exposure (DWD, 2015; Lucas et al., 2019). Worldwide, 76% of new melanoma cases could be attributed to ultraviolet radiation, primarily in North America, Europe, and Oceania (Hiatt and Beyeler, 2021). In Europe, Norway, the Netherlands, Denmark, Sweden and Germany had the highest rate of new melanoma cases per 100,000 population in Europe in 2018 (WCRF, n.d.). Melanoma annually claims  more than 20,000 lives in Europe (Forsea, 2020). In addition to impacts on skin, prolonged exposure to UV radiation is connected to a large proportion of visual impairment world-wide (Lucas et al., 2019).

Projected effects

UV radiation is generally affected by changes in the stratospheric ozone and global climate change. Decreased stratospheric ozone allows more UVB (the higher-frequency, more harmful type of UV) to reach the Earth’s surface. Conversely, increases in cloud cover, pollution, dust, smoke from wildfires and other airborne and waterborne particles related to climate change decreases UV light penetration (SERC, n.d.).

Across Europe, UV radiation trends have varied significantly throughout the past decades. While an increasing trend in UV radiation has been observed for southern and central Europe since the 1990s, it has decreased at higher latitudes, with aerosols (small solid or liquid particles in the air) and cloud coverage affecting these trends. In central Europe, in the period 1947-2017, the changes in aerosols were found to be the main driver of the decadal variations in the surface solar radiation reaching the Earth’s surface (Wild et al., 2021). Data recorded at four European stations during 1996–2017 further reveals that long-term changes in UV are not only mainly driven by changes in aerosols, but also from changes in cloudiness and surface albedo (proportion of sunlight reflected by the earth’s surface), while changes in total ozone play a less significant role (Fountoulakis et al., 2019). In Eastern Europe, between 1979-2015, the decrease in both total ozone and cloudiness led to an increase of daily UV radiation at ground level that could affect human skin (the erythemal daily dose) by up to 5-8% per decade (Chubarova et al., 2020).

Climate change is modifying UV exposure and affecting how people and ecosystems respond to UV. For Nordic countries, exceptionally long periods of clear skies and recorded dry and warm conditions seem to be the main cause for unusually high UVI values in summer 2018. Such exceptional conditions are part of record-setting heat waves that affected large parts of central and Northern Europe and have been occurring more frequently in recent decades. The underpinning link to climate change inducing Arctic warming and increasing heat waves is under investigation (Bernhard et al., 2020).

Future regional UV radiation projections under climate change depend mostly on cloud trends, aerosol and water vapour trends and stratospheric ozone. For Central Europe, the IPCC Assessment Report 6 assigns low confidence to an increase in surface radiation, owing in particular to disagreement in cloud cover across global and regional models, as well as water vapour. Regional and global studies indicate, however, that there is medium confidence in increasing radiation over Southern Europe and decreasing radiation over Northern Europe (Ranasinghe et al., 2021).

Furthermore, rising temperatures associated with climate change result in behavioural changes, such as increasing time outdoors and shedding of protective clothing that lead to more UV radiation exposure and skin cancers than with lower temperatures. Nevertheless, when temperatures are very high, people spend less time outside than they do with small increases in temperature, therefore reducing exposure to UV radiation. Although social behaviours are hard to predict, the effects of human behaviour in response to temperature increases are likely to be a more important factor for skin cancer rates than the increase in UV radiation itself (Hiatt and Beyeler, 2020).

Policy responses

The prevention of negative health effects of UV includes a two-pronged approach in policy, aiming at reducing UV radiation itself on the one hand, and raising awareness of health risks from UV exposure on the other.  Firstly, the 1987 Montreal Protocol (UNEP 2018) and the 2009 EU ‘Ozone Regulation’ aim at decreasing the depletion of stratospheric ozone. These policies have led to reduced consumption of ozone-depleting substances globally and in the EU, which has already met its goals in line with the Montreal Protocol, but actively continues its phase-out. As a result, the extent of the ozone hole (i.e. the part of the stratosphere over the Antarctic most severely depleted of ozone) seems to be levelling off.  However, more needs to be done to reduce the global use of ozone-depleting substances (EEA, 2021).

Secondly, educational campaigns aimed at raising awareness of the dangers associated with excessive exposure to UV are carried out at the international level. For example, the INTERSUN Programme (a collaboration between WHO, the United Nations Environment Programme, the World Meteorological Organization, the International Agency on Cancer Research and the International Commission on Non-Ionizing Radiation Protection) promotes and evaluates research on the health effects of UV radiation, and develops an appropriate response through guidelines, recommendations and information dissemination (WHO, N.D.). In 2006, the European Commission introduced a recommendation on the labelling of sunscreen products to allow consumers to make informed choices (2006/647/EC). 

At the national level, many EU member states provide UV Index (UVI) forecasts and associated health advice. The UVI is often reported during summer months along with the weather forecast in newspapers, on TV and on the radio. UVI forecasts in national languages are available for many European countries from their meteorological services (see examples here). UVI viewers in English and for the whole of Europe are available from e.g.  the German Meteorological Service, the Dutch Tropospheric Emission Monitoring Internet Service and the Finnish Meteorological Institute. 

References