Ultraviolet radiation
Ultraviolet (UV) radiation is a type of electromagnetic radiation emitted by the sun, characterized by wavelengths shorter than visible light but longer than X-rays. It is divided into three bands: UV-A (320-400 nm), UV-B (280-320 nm), and UV-C (200-280 nm). While a small amount of UV radiation is essential for human health, promoting vitamin D synthesis and acting as a germicide, excessive exposure can lead to harmful effects, including sunburn, skin cancers, and cataracts. The ozone layer in the stratosphere plays a crucial role in protecting life on Earth by absorbing most UV-B radiation, but human activities have contributed to its depletion, allowing more UV radiation to reach the surface.
The consequences of increased UV exposure are profound, impacting not only human health but also terrestrial and aquatic ecosystems. Changes in UV radiation levels can alter the cycling of essential nutrients and affect species survival, with particular sensitivity noted in amphibians and marine life. Moreover, increased UV radiation can damage materials such as plastics and paints, leading to accelerated degradation of structures exposed to sunlight. As the ozone layer gradually heals, ongoing monitoring is essential to understand how these changes will influence health and environmental dynamics in the future.
Ultraviolet radiation
Definition
The sun produces ultraviolet (UV) light. UV light is a portion of the electromagnetic spectrum with wavelengths shorter than those of visible light but longer than those of x-rays. UV light wavelengths—shorter than the shortest wavelength of visible light, violet—are too short to be seen by the human eye (ultraviolet literally means “beyond violet”). UV radiation produced by the sun is commonly split into three bands: UV-A, with wavelengths of 320-400 nanometers; UV-B, with wavelengths of 320-280 nanometers; and UV-C, with wavelengths of 200-280 nanometers. Most people are familiar with UV light through the painful effects of sunburn. A small amount of UV radiation is necessary for the well-being of humans and other organisms because it promotes vitamin D synthesis in humans and acts as a germicide, controlling microbial growth. Too much UV radiation, however, is associated with many harmful effects.
Ozone is a very important part of the upper atmosphere or stratosphere. It absorbs UV rays, forming a physical barrier that protects living organisms from harmful solar UV radiation. Although some of this radiation passes through the and reaches the surface, most of the UV-B radiation entering Earth’s atmosphere is absorbed by the ozone layer. UV-A radiation is not. Consequently, more than 95 percent of the UV radiation that reaches Earth’s surface is UV-A radiation. When UV-B radiation encounters an ozone (O3) molecule, it can split O3 into molecular oxygen (O2) and atomic oxygen (O), which can then recombine with O2 to form O3 in a dynamic equilibrium.
Prior to the twenty-first century, the ozone layer was harmed by a variety of environmental factors disrupting this equilibrium, such as refrigerants, halons, and methyl bromide (a deadly pesticide used on crops). Chlorofluorocarbons, chemicals historically used in many refrigerant systems and aerosols, are broken down by UV light into components that deplete ozone. As atmospheric ozone decreases, UV radiation infiltrates Earth's ecosystems with potentially harmful effects. The intensity of UV-B radiation that reaches the Earth increases by 2 percent for every 1 percent decrease in the ozone layer.
Significance for Climate Change
As the ozone layer decreases in size, it provides less protection from UV light. Consequently, more UV radiation passes through the atmosphere and reaches Earth’s surface. Changes in the amount of UV radiation reaching the planetary surface have many potential consequences for climate change, most of which are interrelated. Heat is generated in the as the ozone layer absorbs UV radiation. The resultant warming of the stratosphere creates a temperature inversion at the boundary between the stratosphere and the troposphere, helping stabilize climatic conditions. The stratosphere becomes cooler as the ozone layer declines, which could ultimately result in the cooling of Earth’s surface, despite more UV light reaching the ground. In July 2014, a team of US and German researchers measured the highest level of ultraviolet radiation ever recorded on Earth's surface, in the Bolivian Andes, where researchers recorded record ultraviolet fluxes in South America. Researchers speculated the increased UV flux may have been caused by ozone depletion and noted that these are signs of what could occur if the ozone thins globally. In 2019, UVI levels measured in the Arctic consistently matched the lower limit of recorded levels due to the stratosphere temperature increase. However, in 2020, the Antarctic ozone hole experienced its longest recorded ozone hole due to record low ozone column measurements. This allowed the UV-B radiation levels in the Arctic to climb to record levels, and UVI reached its highest peak in thirty years. Despite these measurements, the healing process aided by the Montreal Protocol was predicted to regain progress and continue advancement.
A study by the UN Environment Programme showed that some progress was being made. A hole in the ozone layer over Antarctica opens annually and is measured by scientists. In 2024, the hole was smaller than in previous years, although it was still nearly three times the size of the United States. Scientists cautioned that the size of the hole was not cause for alarm because it was below average compared to other years, which indicated that the ozone layer was healing, albeit slowly.
An increase in greenhouse gases (GHGs), however, may offset such surface cooling. In many cases, the same gases are responsible for both ozone destruction and climate change due to the greenhouse effect. For example, chlorofluorocarbons play a major role in ozone layer destruction but also are potent GHGs. As the ozone layer becomes more depleted by GHGs and other chemical contaminants, the amount of UV radiation that reaches the Earth’s surface will increase.
An increase in UV light reaching Earth’s surface impacts human health and the well-being of other organisms and can also degrade nonliving materials. Changes in UV radiation have significant effects on both terrestrial and aquatic ecosystems, with important implications for the cycling of carbon, nitrogen, and other elements. Increased UV light induces carbon release from decaying plant material and nitrogen release from Arctic snow. Changes in UV radiation affect carbon cycling, including its capture through photosynthesis and net ecosystem CO2 exchange through storage and release. UV exposure can also affect the cycling of the mineral nutrients, such as nitrogen, that plants depend on for growth. In aquatic ecosystems, UV radiation impacts the cycling of carbon, nitrogen, sulfur, and metals, affecting numerous life processes.
Many studies have demonstrated that exposure to UV radiation has contributed to a worldwide increase in skin cancers, including malignant melanoma. UV radiation may cause changes in the body’s immune system, which may impair its ability to defend against cancer and facilitate the spread of infectious diseases. A study in the United Kingdom showed that 86 percent of melanomas were attributed to UV exposure, according to the American Cancer Society in 2024. Increased UV-B exposure has also been linked to increased incidence of cataracts, the leading cause of blindness worldwide. Many amphibian population declines have been associated with UV exposure. Increased UV radiation also disrupts insect activity and, consequently, affects organisms that depend on insects.
Plants and animals living in freshwater and marine ecosystems are sensitive to UV radiation. UV-B can penetrate several meters of water and affect the survival and growth of marine invertebrates and algae. High levels of UV radiation can inhibit and growth in some plants, including many food crops, and can also result in declines in forest productivity. UV radiation also damages nonliving material and accelerates the breakdown of many paints and plastics used to construct products and structures regularly exposed to sunlight.
Bibliography
Barnes, P. W., et al. “Environmental Effects of Stratospheric Ozone Depletion, UV Radiation, and Interactions with Climate Change: UNEP Environmental Effects Assessment Panel, Update 2021.” Photochem Photobiol Sci, vol. 21, no. 3, 2022, pp. 275–301. doi.org/10.1007/s43630-022-00176-5. Accessed 9 Dec. 2024.
Cockell, Charles, and Andrew R. Blaustein, eds. Ecosystems, Evolution, and Ultraviolet Radiation. New York: Springer-Verlag, 2001.
Hanslmeir, Arnold. The Sun and Space Weather. 2d ed. Dordrecht, the Netherlands: Springer, 2008.
Iacurci, Jenna. "Depleting Ozone May Lead to Increased Ultraviolet Radiation on Earth." Nature World News. Nature World News, 8 Jul. 2014. Web. 24 Mar. 2015.
Nilsson, Annika. Ultraviolet Reflections: Life Under a Thinning Ozone Layer. New York: John Wiley and Sons, 1996.
"2024 Ozone Hole Ranked 7th-Smallest Since Recovery Began." UN Environment Programme, 31 Oct. 2024, ozone.unep.org/2024-ozone-hole-ranked-7th-smallest-recovery-began. Accessed 9 Dec. 2024.
"UV (Ultraviolet) Radiation and Cancer Risk." American Cancer Society, 26 June 2024, www.cancer.org/cancer/risk-prevention/sun-and-uv/uv-radiation.html. Accessed 9 Dec. 2024.
Vandergriendt, Carly. "What's the Difference between UVA and UVB Rays?" Reviewed by Owen Kramer. Healthline, 12 Sept. 2019, www.healthline.com/health/skin/uva-vs-uvb. Accessed 9 Dec. 2024.