Solar radiation is an important natural factor because it forms the Earth’s climate and has a significant influence on the environment. The ultraviolet part of the solar spectrum (UV) plays an important role in many processes in the biosphere. It has several beneficial effects but it may also be very harmful if UV exceeds ”safe” limits. If the amount of UV radiation is sufficiently high the self-protection ability of some biological species is exhausted and the subject may be severely damaged. This also concerns the human organism.
Changes in the earth's climate affect on the other hand the incoming UV radiation. Clouds, Ozone and Aerosols are the most effective attenuators for radiation. If the eamount changes the UV changes as well.

Total ozone column
The inverse correlation between the total ozone column and the UV-B irradiance has been confirmed by measurements at several locations. These measurements show that long-term changes of the stratospheric ozone layer may modify the UV climatology, particularly at middle and high latitudes. An expected recovery of the ozone layer in the middle of the 21st century should therefore also allow for a stabilisation of UV-B radiation in the next decades.
The present trends and the behaviour of the ozone layer are strongly influenced by radiative, chemical and dynamical processes in the stratosphere. The significance of these processes may be augmented by human activities (e.g. the ”greenhouse effect”) and result in higher short-term variations of the ozone layer and UV-B radiation.

In general clouds decrease the amount of incoming UV radiation. However under certain conditions clouds can enhance UV radiation by reflection. Longer term changes in cloudniness occur also on local scales. Therefore trends in respect to clouds can not be generalized.

During the past years many efforts were undertaken to reduce aersols especially in urban regions. This leads to an increase of UV radiation. However UV reaches only the natural level. The environment benefits from clear air. High poluted air is still a serious factor that may cause health damage due to UV deficienncy like decreased Vitamin D photosynthesis that may result in rickets; a serious problem in many cities around the world.

The negative impacts on human health could be eliminated by a professional public awareness based on, for example, UV Index information. In any case, the next century brings a challenge for a more active and individual control of UV exposure and protective measures, at least for the large photosensitive part of the population.
Other organisms have only their natural adaptive protection possibilities.