Editing Ozone depletion (section)

=== Antarctic ozone hole ===
The discovery of the Antarctic "ozone hole" by [[British Antarctic Survey]] scientists [[Joe Farman|Farman]], [[Brian G. Gardiner (meteorologist)|Gardiner]] and [[Jon Shanklin|Shanklin]] (first reported in a paper in ''[[Nature (journal)|Nature]]'' in May 1985<ref>{{Cite journal | last1 = Farman | first1 = J. C. | author-link1 = Joe Farman| last2 = Gardiner | first2 = B. G. | author-link2 = Brian G. Gardiner (meteorologist)| last3 = Shanklin | first3 = J. D. | author-link3 = Jon Shanklin| doi = 10.1038/315207a0 | title = Large losses of total ozone in Antarctica reveal seasonal ClO<sub>x</sub>/NO<sub>x</sub> interaction |journal=Nature |volume=315 |issue=6016 |pages=207–210 |year=1985 |url=https://www.researchgate.net/publication/246650409| bibcode = 1985Natur.315..207F | s2cid = 4346468 }}</ref>) came as a shock to the scientific community, because the observed decline in polar ozone was far larger than had been anticipated.<ref name="Zehr94">{{cite journal |author=Zehr |first=Stephen C. |year=1994 |title=Accounting for the Ozone Hole: Scientific Representations of an Anomaly and Prior Incorrect Claims in Public Settings |journal=The Sociological Quarterly |volume=35 |issue=4 |pages=603–619 |doi=10.1111/j.1533-8525.1994.tb00419.x |jstor=4121521}}</ref> [[Earth observation satellite|Satellite measurements]] ([[TOMS (sensor)|TOMS]] onboard [[Nimbus 7]]) showing massive depletion of ozone around the [[south pole]] were becoming available at the same time.<ref name="Bhartia McPeters 2018 pp. 335–340">{{cite journal | last1=Bhartia | first1=Pawan Kumar | last2=McPeters | first2=Richard D. | title=The discovery of the Antarctic Ozone Hole | journal=Comptes Rendus Geoscience | publisher=Elsevier BV | volume=350 | issue=7 | year=2018 | issn=1631-0713 | doi=10.1016/j.crte.2018.04.006 | pages=335–340| bibcode=2018CRGeo.350..335B | doi-access=free }}</ref> However, these were initially rejected as unreasonable by data quality control algorithms (they were filtered out as errors since the values were unexpectedly low); the ozone hole was detected only in satellite data when the raw data was reprocessed following evidence of ozone depletion in ''in situ'' observations.<ref name="ReferenceA" /> When the [[software]] was rerun without the flags, the ozone hole was seen as far back as 1976.<ref>[http://ozonewatch.gsfc.nasa.gov/facts/history.html History and politics] {{Webarchive|url=https://web.archive.org/web/20161005132113/http://ozonewatch.gsfc.nasa.gov/facts/history.html |date=2016-10-05 }} accessed September 30, 2016.</ref>

[[Susan Solomon]], an atmospheric chemist at the [[National Oceanic and Atmospheric Administration]] (NOAA), proposed that [[chemical reaction]]s on [[polar stratospheric cloud]]s (PSCs) in the cold [[Antarctic]] [[stratosphere]] caused a massive, though localized and seasonal, increase in the amount of [[chlorine]] present in active, ozone-destroying forms. The polar stratospheric clouds in Antarctica are only formed at very low temperatures, as low as −80&nbsp;°C, and early spring conditions. In such conditions the [[ice crystals]] of the cloud provide a suitable surface for conversion of unreactive chlorine compounds into reactive chlorine compounds, which can easily deplete ozone.

Moreover, the [[polar vortex]] formed over [[Antarctica]] is very tight and the reaction occurring on the surface of the cloud crystals is far different from when it occurs in atmosphere. These conditions have led to ozone hole formation in Antarctica. This [[hypothesis]] was decisively confirmed, first by [[laboratory]] measurements and subsequently by direct measurements, from the ground and from high-altitude [[airplane]]s, of very high concentrations of [[chlorine monoxide]] (ClO) in the Antarctic stratosphere.<ref>{{Cite journal | last1 = Solomon | first1 = P. M. | last2 = Connor | first2 = B. | last3 = De Zafra | first3 = R. L. | last4 = Parrish | first4 = A. | last5 = Barrett | first5 = J. | last6 = Jaramillo | first6 = M. | doi = 10.1038/328411a0 | title = High concentrations of chlorine monoxide at low altitudes in the Antarctic spring stratosphere: Secular variation | journal = Nature | volume = 328 | issue = 6129 | pages = 411–413 | year = 1987 | bibcode = 1987Natur.328..411S | s2cid = 4335797 }}</ref>

Alternative hypotheses, which had attributed the ozone hole to variations in solar [[Ultraviolet|UV radiation]] or to changes in atmospheric circulation patterns, were also tested and shown to be untenable.<ref>{{cite book |last1=Reddy |first1=Jeevananda |title=Climate Change Myths and Realities |date=4 November 2008 |page=32 |url=https://www.scribd.com/doc/8963733/Climate-Change-Myths-and-Realities |access-date=20 December 2018}}</ref>

Meanwhile, analysis of ozone measurements from the worldwide network of ground-based Dobson spectrophotometers led an international panel to conclude that the ozone layer was in fact being depleted, at all latitudes outside of the tropics.<ref name="epa.gov" /> These trends were confirmed by satellite measurements. As a consequence, the major halocarbon-producing nations agreed to phase out production of CFCs, halons, and related compounds, a process that was completed in 1996.

Since 1981 the [[United Nations Environment Programme]], under the auspices of the World Meteorological Organization, has sponsored a series of technical reports on the [[Scientific Assessment of Ozone Depletion]], based on satellite measurements. The 2007 report showed that the hole in the ozone layer was recovering and the smallest it had been for about a decade.<ref>{{cite news |title=Ozone hole closing up, research shows |url=http://abc.net.au/news/stories/2007/11/16/2092527.htm |archive-url=https://archive.today/20120715114821/http://abc.net.au/news/stories/2007/11/16/2092527.htm |url-status=dead |archive-date=July 15, 2012 |work=[[ABC News (United States)|ABC News]] |publisher=Australian Broadcasting Commission |date=November 16, 2007 }}</ref>

A 2010 report found, "Over the past decade, global ozone and ozone in the Arctic and Antarctic regions is no longer decreasing but is not yet increasing. The ozone layer outside the Polar regions is projected to recover to its pre-1980 levels some time before the middle of this century. In contrast, the springtime ozone hole over the Antarctic is expected to recover much later."<ref>{{cite news |title=New report highlights two-way link between ozone layer and climate change |url=http://www.unep.org/Documents.Multilingual/Default.asp?DocumentID=647&ArticleID=6751&l=en&t=long |work=UNEP News Center |date=November 16, 2010 |access-date=September 18, 2010 |archive-date=December 5, 2010 |archive-url=https://web.archive.org/web/20101205143536/http://www.unep.org/Documents.Multilingual/Default.asp?DocumentID=647&ArticleID=6751&l=en&t=long |url-status=dead }}</ref>

In 2012, [[NOAA]] and [[NASA]] reported "Warmer air temperatures high above the Antarctic led to the second smallest season ozone hole in 20 years averaging 17.9 million square kilometres. The hole reached its maximum size for the season on Sept 22, stretching to 21.2 million square kilometres."<ref>{{cite web|title=NOAA, NASA: Antarctic ozone hole second smallest in 20 years |url=http://www.noaanews.noaa.gov/stories2012/20121024_antarcticozonehole.html |date=October 24, 2012}}</ref> A gradual trend toward "healing" was reported in 2016<ref name="healing" /> and then in 2017.<ref>{{Cite journal|last1=Kuttippurath|first1=Jayanarayanan|last2=Nair|first2=Prijitha J.|date=2017-04-03|title=The signs of Antarctic ozone hole recovery|journal=Scientific Reports|language=en|volume=7|issue=1|pages=585|doi=10.1038/s41598-017-00722-7|issn=2045-2322|pmc=5429648|pmid=28373709|bibcode=2017NatSR...7..585K}}</ref> It is reported that the recovery signal is evident even in the ozone loss saturation altitudes.<ref>{{Cite journal|last1=Kuttippurath|first1=J.|last2=Kumar|first2=P.|last3=Nair|first3=P. J.|last4=Pandey|first4=P. C.|date=2018-11-21|title=Emergence of ozone recovery evidenced by reduction in the occurrence of Antarctic ozone loss saturation|journal=npj Climate and Atmospheric Science|language=en|volume=1|issue=1|page=42 |doi=10.1038/s41612-018-0052-6|bibcode=2018npCAS...1...42K |issn=2397-3722|doi-access=free}}</ref>

The hole in the Earth's ozone layer over the South Pole has affected atmospheric circulation in the Southern Hemisphere all the way to the equator.<ref>{{cite web |url=http://www.earth.columbia.edu/articles/view/2802 |title=Study Links Ozone Hole to Weather Shifts |publisher=The Earth Institute – Columbia University |date=April 22, 2011 |access-date=December 21, 2012}}</ref> The ozone hole has influenced atmospheric circulation all the way to the tropics and increased rainfall at low, subtropical latitudes in the Southern Hemisphere.<ref>{{Cite web |title=Study Links Ozone Hole to Weather Shifts – The Earth Institute – Columbia University |url=https://www.earth.columbia.edu/articles/view/2802 |access-date=2022-07-13 |website=www.earth.columbia.edu}}</ref>