GE-I-8: Index – case study | Umweltbundesamt

GE-I-8: Index – case study

UV radiation is the main cause of skin cancer. It is a disease to which annually more than 300,000 new people in Germany fall prey. Even at stations in lowland areas, almost for half the year, irradiation strengths (UVI ≥3) are reached which can cause sunburn for which sun protection is recommended. UV irradiation strength varies with latitude, altitude and the current weather scenario, especially cloud cover.

UV radiation

UV radiation is the energy-richest part of optical radiation and cannot be seen by the human eye. In healthy humans, UV radiation initiates the important vitamin D production by the body. At the same time, however, it can lead to serious medical conditions which may manifest either directly or at some later stage in life, both in the eyes and in the skin³². UV radiation damages the genetic material. It is the main cause of skin cancer and has been assigned by the IARC (International Agency for Research on Cancer) to the highest risk category, Group 1, as ‘carcinogenic to humans’³³. UV-related cancerous conditions constitute a major stress on the health of the person affected, and they inflict high expenditure on the public health service³⁴. In Germany the incidence of light skin cancer (both in terms of basal cell and squamous cell carcinoma) quadrupled in respect of men over the past 30 years, whilst it quintupled in respect of women. With regard to malignant melanoma, the incidence has increased approximately fourfold since the 1970s^{35 35} According to extrapolations from data collected by the Hautkrebsregister (Skin Cancer Registry) of Schleswig-Holstein, currently every year some 300,000 people are newly diagnosed with skin cancer in Germany³⁶.

UV-related damage to health can basically afflict anyone. In particular children are affected, as their skin and eyes are more sensitive to UV radiation than adults. Likewise people who work outdoors, thus being exposed more long-term, are subject to a high risk. At any age, sunburn will increase the risk of malignant melanoma roughly twofold – in childhood even two- to threefold. Damage caused by UV radiation will cumulate over a lifetime³⁷.

Although the depletion of the stratospheric ozone layer arising from anthropogenic influences increases the UV irradiation close to the ground, it is of less importance for UV burdens in Germany. Nevertheless, the recovery of the ozone layer seems to be delayed on account of several influential factors. For the northern hemisphere, a return to ozone column values as experienced in 1980 is to be expected approximately by 2035³⁸. Furthermore, so-called ‘low ozone events’ can occur which can cause unexpectedly high UV irradiation strengths lasting for just a few days. The origin of this phenomenon may be sought year-round in dynamic processes in the atmosphere and, especially in spring, in the wintry ozone depletion above the arctic^{39 39 39}. Low-ozone events in spring are particularly relevant in terms of health, as the human skin is still especially sensitive to UV radiation at that time of year. At the end of March / early April in 2020, for example, the UV index in southern Germany (Munich) increased from 3 to 6, owing to such a low-ozone event combined with the weather pattern prevailing at the time⁴⁰. A study has indicated that the frequency of low-ozone events in spring has decreased over the past two decades⁴¹. At the same time, this study demonstrates that spring seems to be the season which is most affected by low-ozone events. As far as the development of low ozone events in the northern hemisphere in the future progress of the 21st century is concerned, no uniform findings have yet emerged from this study^{42 42 42}.

In Germany the number of sunshine hours has changed in the course of recent decades. Until the 1980s, in Germany and the entire northern hemisphere, a continuous decrease in sunshine hours (1951–1980 by roughly 11 %, linear trend) was recorded⁴³. The reason for this so-called ‘global dimming’ effect is attributed to the increasing contamination of the atmosphere with industrial gas emissions and the associated formation of clouds⁴⁴. Approximately since the middle of the 1980s, the aerosol concentration has decreased in Germany, thanks to the successful implementation of air pollution control measures⁴⁵, followed by an increasing number of annual sunshine hours (1981–2022 by roughly 19 %). This ‘global brightening’ effect is essentially due to a successful international air pollution control policy rather than representing a direct impact of climate change^{46 46}. The basic relationship between a change in radiation intensity and climate change is currently an important focal point of research. For example, data collected in the period of 1996 to 2017 at four European stations show that long-term changes in UV radiation depend, above all, on changes in aerosols, cloud cover and surface reflexion capacity (albedo)⁴⁷.

The intensity of UV radiation is indicated in terms of the UV index (UVI) – a worldwide homogeneous standard for the daily peak value expected to be measured at ground level (30-minute mean) of the UV irradiation strength capable of causing sunburn⁴⁸.The higher the UVI, the higher the UV irradiation strength and the faster sunburn can develop on unprotected skin.

The case study presented in this report is based on the values measured at measuring stations which are part of the UV measuring network. Taking the latitude into account (the UV Index increases from north to south) as well as the altitude (the UV Index is higher in mountains than in lowland areas), the stations have been assigned to four natural spaces. The illustration shows all days with UV values of 3 and more, given that from UV Index 3 upwards, it is already recommended to take measures for sun protection. Given that for a UV Index of 8, the recommendations for taking sun protection have been stepped up further, the days with UVI values equal to or higher than 8 are illustrated. For every station, the days with the relevant values for each year are totalled, and then the mean is calculated across the stations in the natural space concerned.

There are distinct regional differences. In lowland areas, almost for half the year, irradiation strengths are reached for which sun protection is recommended. In the uplands, the foothills of the Alps and in the high mountains, this applies to 200 days and more annually. The period in question does not yet permit any statements on trend. There is a need for further research into the climate-change related changes in influential factors affecting UV radiation close to ground level.