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Global Climate Change Digest
A Guide to Information on Greenhouse Gases and Ozone Depletion
Published July 1988 through June 1999

FROM VOLUME 12, NUMBER 1, JANUARY 1999

JOURNAL ARTICLES...
INCREASED UV-B EXPOSURES

The most recent issue of Journal of Photochemistry and Photobiology (Elsevier) was devoted to a series of reviews that summarized the effects that are expected to be produced by the higher irradiances of ultraviolet light (especially type B ultraviolet radiation, UV-B) at the surface of the Earth because of the thinning of the ozone layer of the stratosphere by chlorofluorocarbons and other industrial emissions.

Item #d99jan12

“Changes in Biologically Active Ultraviolet Radiation Reaching the Earth’s Surface,” Sasha Madronich et al., J. Photochem. Photobiol. 48 (1-3), 5-19 (1998).

Stratospheric ozone levels are at the lowest they have been since the start of measurement, so UV-B exposures at the surface of the Earth are expected to be the highest during that same period. Since the 1970s, sunburning has increased 4 to 7% in the Northern Hemisphere, 6% in the Southern, 130% in Antarctica, and 22% in the Arctic. On-the- ground measurements of UV irradiances during the summer show that Southern Hemisphere values exceed Northern values by 40%. The current best prognostications of UV irradiance call for a slow recovery during the next half-century to levels comparable to those before ozone depletion.

Item #d99jan13

“Health Risks,” J. Longstreth et al.,J. Photochem. Photobiol. 48 (1-3), 20-39 (1998).

UV-B radiation causes damage to the eyes (the most common being photokeratitis, or snowblindness), immune systems, and skin. Suppression of immune responses to a number of antigens has been experimentally demonstrated in humans and animals. For light-skinned subjects, UV exposure is the most important factor in basal and squamous-cell carcinomas and melanomas. Recent research indicates that early exposure (before age 15) increases risk most. Projections call for cataract incidence to peak at 3 additional cases per 100,000 people and skin-cancer occurrences at 7 per 100,000 by midcentury.

Item #d99jan14

“Effects of Increased Solar Ultraviolet Radiation on Terrestrial Ecosystems,” M. M. Caldwell et al.,J. Photochem. Photobiol. 48 (1-3), 40-52 (1998).

UV-B affects plants, microbes, and some animals. Plant effects include changes (increases and decreases) in susceptibility to insect attack and pathogens, changes in competitive balances within plant communities, and changes in nutrient cycling. Direct effects on plants usually take the form of genetic alteration rather than of damage; this can be addressed through genetic engineering or breeding. Some crop yields are decreased by increased UV. The magnitude and direction of most ecosystem effects are not known or easily predicted.

Item #d99jan15

“Effects on Aquatic Ecosystems,” D.-P. Hader et al.,J. Photochem. Photobiol. 48 (1-3), 53-68 (1998).

Radiation breaks down high-molecular-weight substances and is important in cycling of carbon in the aquatic environment. Bacterioplankton, which take up dissolved organic carbon and remineralize the carbon, are more prone to UV-B stress than larger organisms. UV affects the growth, development, and physiological responses of cyanobacteria, which are major constituents of microbial mats. UV damages phytoplankton at the molecular through community levels by affecting growth, reproduction, photosynthetic enzymes, and photosynthetic pigments. In the Arctic and Antarctic oceans, phytoplankton are exposed to more UV-B because of the shallow water and its pronounced stratification. Many economically important fish spawn in these shallows and the eggs and larvae are exposed to the UV radiation; reduced productivity is likely but undemonstrated. Macroalgae and sea grasses are very sensitive to UV, especially through photoinhibition. One study showed a 4 to 23% photoinhibition under the ozone hole. UV-B-sensitive aquatic organisms include zooplankton, sea urchins, corals, and amphibians. Freshwater systems respond to a complex array of conditions, stressors, and interspecies influences; UV-B sensitivity is an added stress factor. An array of factors that influence in-water attenuation of UV is being studied for the first time with a network of underwater dosimeters for continuous monitoring at stations from Sweden to the Canary Islands.

Item #d99jan16

“Effects of Enhanced Solar Ultraviolet Radiation on Biogeochemical Cycles,” R. G. Zepp, T. V. Callaghan, and D. J. Erickson,J. Photochem. Photobiol. 48 (1-3), 69-82 (1998).

UV-B alters the chemical composition of plant tissue, degrades dead plant matter, releases CO from charcoal, modifies the makeup of microbial-decomposer communities, and affects the nitrogen-fixing capabilities of plants and microorganisms. Studies have indicated that organic matter is the major regulator of UV-B penetration of bodies of water and that UV clarifies water and changes its light qualities. It has both positive and negative effects on microbes that can affect carbon and mineral cycling and the uptake and release of greenhouse gases.

Item #d99jan17

“Changes in Tropospheric Composition and Air Quality,” X. Tang et al.,J. Photochem. Photobiol. 48 (1-3), 83-95 (1998).

UV-B increases chemical activity in the lower atmosphere, especially reactions of nitrogen oxides and hydrocarbons. Ironically, UV-B decomposes tropospheric ozone in clean environments and produces it in polluted atmospheres. UV-B increases the rate at which primary pollutants are removed from the air (partly by producing secondary pollutants) and increases hydroxyl-radical concentrations. As a result, higher atmospheric concentrations are expected if UV-B irradiance in the troposphere increases.

Item #d99jan18

“Effects of Increased Solar Ultraviolet Radiation on Materials,” A. L. Andrady et al.,J. Photochem. Photobiol. 48 (1-3), 96-103 (1998).

UV-B adversely affects the physical properties of polymers, limiting their lifetimes. Although some spectral- sensitivity data have been published recently, little dose-response work has been done on plastics exposed to UV-B. Both types of information are necessary before the effects of UV-B exposure can be quantified and predicted. In the meantime, the useful lifetime of such materials can be extended by increasing the amount of photostabilizers incorporated into them.