New facts on environmental effects of ozone depletion and its interactions with climate change

Summary by  GreenFacts of the 2011 Report from the United Nations Environment Programme, Environmental Effects Assessment Panel.

New studies suggest that stratospheric ozone depletion increased UV-B radiation reaching the Earth’s surface can influence biological processes by driving large scale climate change events. Meanwhile, models suggest also that in the first half of the 21st century the recovery of ozone and changes in cloudiness will result in decreases in surface erythemal irradiance by 2–10% at mid-latitudes, and by up to 20% at northern and 50% at southern high latitudes.

Reactions driven by solar UV radiation, coupled with a range of effects caused by climate change, can significantly alter carbon cycling in aquatic and terrestrial ecosystems by changing the nature and biological availability of organic carbon and nitrogen in decreasing the capacity of the oceans in the polar regions to take up carbon dioxide from the atmosphere.

Ozone loss, UV exposure and human health

Recent studies and estimates of the human health impact of air pollution highlight the potentially large impact of the coupled effects of stratospheric ozone depletion and climate change.

Without the Montreal Protocol, by 2065, erythemally weighted UV radiation would have been increased by a factor of 3 or more at all latitudes. Fortunately, an upward trend in total ozone over Antarctica since the late 1990s is detectable and is presumably due to reduction in CFCs.

The report highlights that exposure to solar UV-B radiation causes various types of skin cancers and where monitored, the annual incidence rate of these cancers has increased over the past 30 years and is projected to continue to increase, particularly in those aged over 50 years. In particular, melanoma is now more definitively linked with solar UV-B exposure as a risk factor, particularly episodes of severe sunburn; its incidence continues to increase.

Epidemiological evidence reported in the study suggests that conjunctival melanomas (on the external surface of the eye) but not intraocular (internal) melanomas are likely to be induced by exposure to solar UV radiation.  Exposure to solar UV radiation contributes to the development of Merkel cell carcinoma (MCC), an uncommon but aggressive tumour that occurs on sun-exposed body sites. MCC is found most frequently in elderly men, and survival is poorer than for melanoma.

Changes in the climate resulting from depletion of stratospheric ozone and global warming might also result  in a rise in the incidence and prevalence of water-borne and vector-borne infections.

UV-B radiation is also an essential ingredient in the formation of many photochemical pollutants, including ground-level ozone and a large portion of fine particulates. Therefore, quality of air at ground-level can be improved without significant increases in exposures to UV radiation.

 The paradox of vitamin D

Low levels of exposure to the sun and/or of vitamin D are associated with an increased risk of multiple sclerosis, diabetes and some infectious diseases. Meanwhile,  the potential benefit of vitamin D, produced as a result of increased exposure to solar UV-B radiation, should be balanced against the harmful outcomes of such exposure, including skin cancers and cataract. A too low or too high vitamin D status may equally not be beneficial. This has been shown for prostate cancer, tuberculosis, premature aging, and mortality, says the report.

Although many health benefits have been proposed for vitamin D, some caution is thus required, particularly in situations where the vitamin D levels are increased through dietary supplements rather than by natural sunlight exposure.

 Environmental impact

Evidence continues to demonstrate that solar UV-B radiation is an important regulator of interactions between plants and consumer organisms, such as pests and pathogens. A major breakthrough has been made in the understanding of the molecular mechanisms at the photoreceptor level  that control plant responses to UV-B radiation. However, while the mechanisms by which UV-B radiation affects aquatic organisms are now well-known in many cases, understanding of the magnitude of biogeochemical responses in relation to these interactions remains very limited. For example, many invertebrates, including zooplankton, have a variety of successful defences that can reduce the negative impacts of elevated UV exposure.

The report explains how combined effects of changes in solar UV-B radiation and climate can reduce biological carbon fixation in aquatic systems and thus modify oceanic uptake of CO2. Climate change may also reduce up-welling and availability of nutrients for phytoplankton resulting in further interactions with solar UV radiation on biological fixation of carbon.

In terrestrial ecosystems, exposure to solar UV radiation affects below-ground as well as above-ground processes, with consequences for ecosystem carbon balance.

Reference :  the Environmental Effects Assessment Panel (EEAP)  produces a detailed report every four years; the most recent was published in 2010 (Photochem. Photobiol. Sci., 2011, 10, 173–300). The parties to the Montreal Protocol are informed by three panels of experts. One of these is the Environmental Effects Assessment Panel (EEAP), which deals with two focal issues. The first focus is the effects of increased UV radiation on human health, animals, plants, biogeochemistry, air quality, and materials. The second focus is on interactions between UV radiation and global climate change and how these may affect humans and the environment.

 Source document : United Nations Environment Programme, Environmental Effects Assessment Panel, Environmental effects of ozone depletion and its interactions with climate change: progress report, 2011, Photochem. Photobiol. Sci., 2012, 11, 13–27 | doi:10.1039/C1PP90033A

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