Editing Ozone depletion (section)

=== Biological effects ===
The main public concern regarding the ozone hole has been the effects of increased surface UV radiation on human health. So far, ozone depletion in most locations has been typically a few percent and, as noted above, no direct evidence of health damage is available in most latitudes. If the high levels of depletion seen in the ozone hole were to be common across the globe, the effects could be substantially more dramatic. As the ozone hole over Antarctica has in some instances grown so large as to affect parts of [[Australia]], [[New Zealand]], [[Chile]], [[Argentina]], and [[South Africa]], environmentalists have been concerned that the increase in surface UV could be significant.<ref>{{cite news|url=https://abcnews.go.com/Technology/story?id=119899 |title=Ozone Hole Over City for First Time |first=Ray |last=Lilley |agency=Associated Press |date=October 5, 2000 |access-date=March 13, 2015}}</ref> Excessive ultraviolet radiation (UVR) has reducing effects on the rates of photosynthesis and growth of benthic [[diatom]] communities (microalgae species that increase water quality and are pollution resistant) that are present in shallow freshwater.<ref>{{Cite journal|url=https://www.science.org/doi/10.1126/science.265.5168.97|title=Ecosystem Response to Solar Ultraviolet-B Radiation: Influence of Trophic-Level Interactions|first1=Max L.|last1=Bothwell|first2=Darren M. J.|last2=Sherbot|first3=Colleen M.|last3=Pollock|date=July 6, 1994|journal=Science|volume=265|issue=5168|pages=97–100|doi=10.1126/science.265.5168.97|pmid=17774696 |bibcode=1994Sci...265...97B |s2cid=43683982 }}</ref> Ozone depletion not only affects human health but also has a profound impact on biodiversity. It damages plants and trees at the cellular level, affecting their growth, vitality, photosynthesis, water balance, and defense mechanisms against pests and diseases. This sets off a cascade of ecological impacts, harming soil microbes, insects, wildlife, and entire ecosystems.<ref>{{Cite web |title=Ozone Pollution: An Insidious and Growing Threat to Biodiversity |url=https://e360.yale.edu/features/ozone-pollution-an-insidious-and-growing-threat-to-biodiversity |access-date=2024-04-12 |website=Yale E360 |language=en-US}}</ref>

Ozone depletion would magnify all of the [[Health effects of sun exposure|effects of UV on human health]], both positive (including production of vitamin D) and negative (including sunburn, skin cancer, and cataracts). In addition, increased surface UV leads to increased tropospheric ozone, which is a health risk to humans.<ref>{{Cite journal|last1=Bais|first1=F.|last2=Luca|first2=R. M.|last3=Bornman|first3=J. F.|last4=Williamson|first4=C. E.|last5=Sulzberger|first5=B.|last6=Austin|first6=A. T.|last7=Wilson|first7=S. R.|last8=Andrady|first8=A. L.|last9=Bernhard|first9=G.|last10=McKenzie|first10=R. L.|last11=Aucamp|first11=P. J.|date=2018-02-14|title=Environmental effects of ozone depletion, UV radiation and interactions with climate change: UNEP Environmental Effects Assessment Panel, update 2017.|journal=Photochemical & Photobiological Sciences|volume=17|issue=2|pages=127–179|doi=10.1039/c7pp90043k|issn=1474-905X|pmc=6155474|pmid=29404558}}</ref>

==== Basal and squamous cell carcinomas ====
The most common forms of skin cancer in humans, [[Basal cell carcinoma|basal]] and [[Squamous cell carcinoma|squamous]] cell carcinomas, have been strongly linked to UV-B exposure. The mechanism by which UVB induces these cancers is well understood—absorption of UV-B radiation causes the pyrimidine bases in the DNA molecule to form [[Dimer (chemistry)|dimers]], resulting in transcription errors when the DNA replicates. These cancers are relatively mild and rarely fatal, although the treatment of squamous cell carcinoma sometimes requires extensive reconstructive surgery. By combining epidemiological data with results of animal studies, scientists have estimated that every one percent decrease in long-term stratospheric ozone would increase the incidence of these cancers by 2%.<ref name="gcrio.org-consequnces">{{cite journal |author=de Gruijl, Frank R. |title=Impacts of a Projected Depletion of the Ozone Layer |journal=Consequences |volume=1 |issue=2 |date=Summer 1995 |url=http://www.wvvvv.gcrio.org/CONSEQUENCES/summer95/impacts.html}}</ref>

==== Melanoma ====
Another form of skin cancer, [[Melanoma]], is much less common but far more dangerous, being lethal in about 15–20 percent of the cases diagnosed. The relationship between melanoma and ultraviolet exposure is not yet fully understood, but it appears that both UV-B and UV-A are involved. Because of this uncertainty, it is difficult to estimate the effect of ozone depletion on melanoma incidence. One study showed that a 10 percent increase in UV-B radiation was associated with a 19 percent increase in melanomas for men and 16 percent for women.<ref>{{cite journal |title=Average midrange ultraviolet radiation flux and time outdoors predict melanoma risk |journal=Cancer Res. |volume=62 |issue=14 |pages=3992–6 |year=2002|pmid=12124332 |last1=Fears |first1=T. R. |last2=Bird |first2=C. C. |last3=Guerry d |first3=4th |last4=Sagebiel |first4=R. W. |last5=Gail |first5=M. H. |last6=Elder |first6=D. E. |last7=Halpern |first7=A. |last8=Holly |first8=E. A. |last9=Hartge |first9=P. |last10=Tucker |first10=M. A. }}</ref> A study of people in [[Punta Arenas]], at the southern tip of [[Chile]], showed a 56 percent increase in melanoma and a 46 percent increase in non-melanoma skin cancer over a period of seven years, along with decreased ozone and increased UVB levels.<ref>{{cite journal |title=Skin cancer and ultraviolet-B radiation under the Antarctic ozone hole: southern Chile, 1987–2000 |journal=Photodermatol Photoimmunol Photomed |volume=18 |issue=6 |pages=294–302 |date=December 2002 |pmid=12535025 |doi=10.1034/j.1600-0781.2002.02782.x|last1=Abarca |first1=J. F. |last2=Casiccia |first2=C. C. |s2cid=25748826 }}</ref>

==== Cortical cataracts ====
Epidemiological studies suggest an association between ocular cortical cataracts and UV-B exposure, using crude approximations of exposure and various cataract assessment techniques. A detailed assessment of ocular exposure to UV-B was carried out in a study on Chesapeake Bay Watermen, where increases in average annual ocular exposure were associated with increasing risk of cortical opacity.<ref>{{cite journal |title=Sunlight exposure and risk of lens opacities in a population-based study: the Salisbury Eye Evaluation project |journal=JAMA |volume=280 |issue=8 |pages=714–8 |year=1998 |pmid=9728643|doi=10.1001/jama.280.8.714 |last1=West |first1=S. K. |last2=Duncan |first2=D. D. |last3=Muñoz |first3=B. |last4=Rubin |first4=G. S. |last5=Fried |first5=L. P. |last6=Bandeen-Roche |first6=K. |last7=Schein |first7=O. D. |doi-access=free }}</ref> In this highly exposed group of predominantly white males, the evidence linking cortical opacities to sunlight exposure was the strongest to date. Based on these results, ozone depletion is predicted to cause hundreds of thousands of additional cataracts by 2050.<ref name="Dobson2005">{{Cite journal| author = Dobson, R. | title = Ozone depletion will bring big rise in number of cataracts| journal = BMJ| volume = 331| issue = 7528| pages = 1292–1295| year = 2005| pmc = 1298891 | doi = 10.1136/bmj.331.7528.1292-d               }}</ref>

==== Increased tropospheric ozone ====
Increased surface UV leads to increased [[tropospheric]] ozone. [[Ground-level ozone]] is generally recognized to be a health risk, as ozone is toxic due to its strong [[redox|oxidant]] properties. The risks are particularly high for young children, the elderly, and those with asthma or other respiratory difficulties. At this time, ozone at ground level is produced mainly by the action of UV radiation on [[combustion]] gases from vehicle exhausts.<ref>{{cite web|url=http://epa.gov/airquality/ozonepollution/pdfs/ozonegb.pdf |title=Ozone: Good Up High, Bad Nearby |publisher=EPA |access-date=March 13, 2015 |url-status=unfit |archive-url=https://web.archive.org/web/20130602101003/http://www.epa.gov/airquality/ozonepollution/pdfs/ozonegb.pdf |archive-date=June 2, 2013 }}</ref>

==== Increased production of vitamin D ====
[[Vitamin D]] is produced in the skin by ultraviolet light. Thus, higher UVB exposure raises human vitamin D in those deficient in it.<ref>{{Cite journal|last1=Webb|first1=Ann R.|last2=Engelsen|first2=Ola|date=2006|title=Calculated Ultraviolet Exposure Levels for a Healthy Vitamin D Status|journal=Photochemistry and Photobiology|language=en|volume=82|issue=6|pages=1697–1703|doi=10.1111/j.1751-1097.2006.tb09833.x|pmid=16958558|s2cid=222102318|issn=1751-1097}}</ref> Recent research (primarily since the Montreal Protocol) shows that many humans have less than optimal vitamin D levels. In particular, in the U.S. population, the lowest quarter of vitamin D (<17.8&nbsp;ng/ml) were found using information from the National Health and Nutrition Examination Survey to be associated with an increase in all-cause mortality in the general population.<ref>{{cite journal |title=25-hydroxyl Vitamin D Levels and the Risk of Mortality in the General Population |journal=Arch. Intern. Med. |volume=168 |issue=15 |pages=1629–37 |year=2008 |pmid=18695076 |pmc=2677029 |doi=10.1001/archinte.168.15.1629|last1=Melamed |first1=M. L. |last2=Michos |first2=E. D. |last3=Post |first3=W. |last4=Astor |first4=B. }}</ref> While blood level of vitamin D in excess of 100&nbsp;ng/ml appear to raise blood calcium excessively and to be associated with higher mortality, the body has mechanisms that prevent sunlight from producing vitamin D in excess of the body's requirements.<ref>{{cite journal |author=Vieth |first=R. |year=1999 |title=Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and safety |journal=American Journal of Clinical Nutrition |volume=69 |issue=5 |pages=842–56 |doi=10.1093/ajcn/69.5.842 |pmid=10232622 |doi-access=free}}</ref>

==== Effects on animals ====
A November 2011 report by scientists at the Institute of Zoology in London, England found that [[whale]]s off the coast of California have shown a sharp rise in sun damage, and these scientists "fear that the thinning ozone layer is to blame".<ref>{{cite news |url=http://voices.washingtonpost.com/blog-post/2010/11/sunburned_whales_bad_environme.html |archive-url=https://web.archive.org/web/20120107143640/http://voices.washingtonpost.com/blog-post/2010/11/sunburned_whales_bad_environme.html |url-status=dead |archive-date=January 7, 2012 |title=Sunburned whales: Troubling environment news of the week |publisher=BlogPost (blog) |newspaper=[[The Washington Post]] |date=November 11, 2010 |access-date=March 28, 2011}}</ref> The study photographed and took skin biopsies from over 150 whales in the Gulf of California and found "widespread evidence of epidermal damage commonly associated with acute and severe sunburn", having cells that form when the DNA is damaged by UV radiation. The findings suggest "rising UV levels as a result of ozone depletion are to blame for the observed skin damage, in the same way that human skin cancer rates have been on the increase in recent decades."<ref>{{cite news |author=Thomas, Abbie |url=http://www.abc.net.au/science/articles/2010/11/10/3062051.htm |title=Whales showing more sun damage |publisher=Abc.net.au |date=November 10, 2010 |access-date=March 28, 2011}}</ref> Apart from whales many other animals such as dogs, cats, sheep and terrestrial ecosystems also suffer the negative effects of increased UV-B radiations.<ref>{{Cite journal|last=Mayer|first=S. J.|date=1992-08-08|title=Stratospheric ozone depletion and animal health|url=https://veterinaryrecord.bmj.com/content/131/6/120|journal=Veterinary Record|language=en|volume=131|issue=6|pages=120–122|doi=10.1136/vr.131.6.120|doi-broken-date=2024-11-02 |issn=0042-4900|pmid=1529513|s2cid=22177257}}</ref>

==== Effects on crops ====
An increase of UV radiation would be expected to affect crops. A number of economically important species of plants, such as [[rice]], depend on [[cyanobacteria]] residing on their roots for the retention of [[nitrogen]]. [[Cyanobacteria]] are sensitive to UV radiation and would be affected by its increase.<ref>{{cite journal
|author = Sinha, R. P.
|author2 = Singh, S. C.
|author3 = Häder, D. P.
|title = Photoecophysiology of cyanobacteria
|year = 1999
|journal =Recent Research Developments in Photochemistry and Photobiology
|volume = 3
|pages = 91–101}}</ref> "Despite mechanisms to reduce or repair the effects of increased ultraviolet radiation, plants have a limited ability to adapt to increased levels of UVB, therefore plant growth can be directly affected by UVB radiation."<ref>{{cite web|title=Health and Environmental Effects of Ozone Layer In Plants|url=http://www.epa.gov/ozone/science/effects/|publisher=U.S Environmental Protection Agency|access-date=November 12, 2013|date=2013-02-15}}</ref>

==== Effects on plant life ====

Over the years, the Arctic ozone layer has depleted severely. As a consequence species that live above the snow cover or in areas where snow has melted abundantly, due to hot temperatures, are negatively impacted due to UV radiation that reaches the ground.<ref>{{Cite journal |last1=Barnes |first1=P. W. |last2=Robson |first2=T. M. |last3=Neale |first3=P. J. |last4=Williamson |first4=C. E. |last5=Zepp |first5=R. G. |last6=Madronich |first6=S. |last7=Wilson |first7=S. R. |last8=Andrady |first8=A. L. |last9=Heikkilä |first9=A. M. |last10=Bernhard |first10=G. H. |last11=Bais |first11=A. F. |date=2022-03-01 |title=Environmental effects of stratospheric ozone depletion, UV radiation, and interactions with climate change: UNEP Environmental Effects Assessment Panel, Update 2021 |url=https://doi.org/10.1007/s43630-022-00176-5 |journal=Photochemical & Photobiological Sciences |language=en |volume=21 |issue=3 |pages=275–301 |doi=10.1007/s43630-022-00176-5 |issn=1474-9092 |pmc=8860140 |pmid=35191005}}</ref> Depletion of the ozone layer and allowing excess UVB radiation would initially be assumed to increase damage to plant DNA. Reports have found that when plants are exposed to UVB radiation similar to stratospheric ozone depletion, there was no significant change in plant height or leaf mass, but showed a response in shoot biomass and leaf area with a small decrease.<ref>{{Cite journal|last1=Searles|first1=Peter S.|last2=Flint|first2=Stephan D.|last3=Caldwell|first3=Martyn M.|date=2001-03-01|title=A meta-analysis of plant field studies simulating stratospheric ozone depletion|journal=Oecologia|language=en|volume=127|issue=1|pages=1–10|doi=10.1007/s004420000592|pmid=28547159|bibcode=2001Oecol.127....1S|s2cid=7049908|issn=1432-1939}}</ref> However, UVB radiation has been shown to decrease quantum yield of photosystem II.<ref>{{Cite journal|last1=Xiong|first1=Fusheng S.|last2=Day|first2=Thomas A.|date=2001-02-01|title=Effect of Solar Ultraviolet-B Radiation during Springtime Ozone Depletion on Photosynthesis and Biomass Production of Antarctic Vascular Plants|journal=Plant Physiology|language=en|volume=125|issue=2|pages=738–751|doi=10.1104/pp.125.2.738|issn=0032-0889|pmid=11161031|pmc=64875}}</ref> UVB damage only occurs under extreme exposure, and most plants also have UVB absorbing flavonoids which allow them to acclimatize to the radiation present. Plants experience different levels of UV radiation throughout the day. It is known that they are able to shift the levels and types of UV sunscreens (i.e. flavonoids), that they contain, throughout the day. This allows them to increase their protection against UV radiation.<ref>{{Cite journal |date=2017 |title=Environmental effects of ozone depletion and its interactions with climate change: Progress report, 2016 |url=http://xlink.rsc.org/?DOI=C7PP90001E |journal=Photochemical & Photobiological Sciences |language=en |volume=16 |issue=2 |pages=107–145 |doi=10.1039/C7PP90001E |issn=1474-905X |pmc=6400464 |pmid=28124708|last1=United Nations Environment Programme |first1=Environmental Effects Assessment Panel |hdl=11336/183828 }}</ref> Plants that have been affected by radiation throughout development are more affected by the inability to intercept light with a larger leaf area than having photosynthetic systems compromised.<ref>{{Cite journal|last1=Allen|first1=Damian J.|last2=Nogués|first2=Salvador|last3=Baker|first3=Neil R.|date=1998-11-01|title=Ozone depletion and increased UV-B radiation: is there a real threat to photosynthesis?|url=https://academic.oup.com/jxb/article/49/328/1775/516230|journal=Journal of Experimental Botany|language=en|volume=49|issue=328|pages=1775–1788|doi=10.1093/jxb/49.328.1775|issn=0022-0957|doi-access=free}}</ref> Damage from UVB radiation is more likely to be significant on species interactions than on plants themselves.<ref>{{Cite journal|last=Björn|first=Lars Olof|date=1996-12-01|title=Effects of ozone depletion and increased UV-B on terrestrial ecosystems|journal=International Journal of Environmental Studies|volume=51|issue=3|pages=217–243|doi=10.1080/00207239608711082|bibcode=1996IJEnS..51..217B |issn=0020-7233}}</ref>

Another significant impact of ozone depletion on plant life is the stress experienced by plants when exposed to UV radiation. This can cause a decrease in plant growth and an increase in oxidative stress, due to the production of nitric oxide and hydrogen peroxide.<ref>{{Cite journal |last1=Bornman |first1=J. F. |last2=Barnes |first2=P. W. |last3=Robinson |first3=S. A. |last4=Ballaré |first4=C. L. |last5=Flint |first5=S. D. |last6=Caldwell |first6=M. M. |date=2015 |title=Solar ultraviolet radiation and ozone depletion-driven climate change: effects on terrestrial ecosystems |url=http://xlink.rsc.org/?DOI=C4PP90034K |journal=Photochemical & Photobiological Sciences |language=en |volume=14 |issue=1 |pages=88–107 |doi=10.1039/C4PP90034K |pmid=25435216 |s2cid=10176384 |issn=1474-905X|doi-access=free |hdl=20.500.11937/28562 |hdl-access=free }}</ref> In areas where substantial ozone depletion has occurred, increased UV-B radiation reduces terrestrial plant productivity (and likewise carbon sequestration) by about 6%.<ref>{{Cite journal |date=2011 |title=Environmental effects of ozone depletion and its interactions with climate change: 2010 assessment : Executive summary |url=http://xlink.rsc.org/?DOI=c0pp90043e |journal=Photochemical & Photobiological Sciences |language=en |volume=10 |issue=2 |pages=178–181 |doi=10.1039/c0pp90043e |pmid=21253669 |s2cid=40238255 |issn=1474-905X|doi-access=free }}</ref><ref>{{Cite journal |last1=Björn |first1=L. O. |last2=Callaghan |first2=T. V |last3=Gehrke |first3=C. |last4=Johanson |first4=U. |last5=Sonesson |first5=M. |date=November 1999 |title=Ozone depletion, ultraviolet radiation and plant life |url=https://doi.org/10.1016/S1465-9972(99)00038-0 |journal=Chemosphere – Global Change Science |volume=1 |issue=4 |pages=449–454 |bibcode=1999ChGCS...1..449B |doi=10.1016/s1465-9972(99)00038-0 |issn=1465-9972}}</ref>

Moreover, if plants are exposed to high levels of UV radiation, it can elicit the production of harmful [[volatile organic compound]]s, like isoprenes. The emission of isoprenes into the air, by plants, can severely impact the environment by adding to air pollution and increasing the amount of carbon in the atmosphere, ultimately contributing to climate change.<ref>{{Cite journal |last1=Bornman |first1=Janet F. |last2=Barnes |first2=Paul W. |last3=Robson |first3=T. Matthew |last4=Robinson |first4=Sharon A. |last5=Jansen |first5=Marcel A. K. |last6=Ballaré |first6=Carlos L. |last7=Flint |first7=Stephan D. |date=2019 |title=Linkages between stratospheric ozone, UV radiation and climate change and their implications for terrestrial ecosystems |url=http://xlink.rsc.org/?DOI=C8PP90061B |journal=Photochemical & Photobiological Sciences |language=en |volume=18 |issue=3 |pages=681–716 |doi=10.1039/C8PP90061B |pmid=30810560 |hdl=10138/307029 |s2cid=73506953 |issn=1474-905X}}</ref>