February 28, 2007
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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
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.
Changes in Biologically Active Ultraviolet Radiation Reaching the
Earths 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.
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.
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.
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.
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.
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
Effects of Increased Solar Ultraviolet Radiation on Materials,
A. L. Andrady et al.,J. Photochem. Photobiol. 48 (1-3),
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.
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