Editing Ozone depletion (section)

== Prospects of ozone depletion ==
[[File:Ozone hole recovery.jpg|thumb|upright=1.7|Ozone levels stabilized in the 1990s following the Montreal Protocol, and have started to recover. They are projected to reach pre-1980 levels before 2075.<ref name=nasa-recovery-projection/>]]
[[File:TotalCl NOAA-HATS.png|thumb|right|upright=1.7|Ozone-depleting gas trends]]

Since the adoption and strengthening of the [[Montreal Protocol]] has led to reductions in the emissions of CFCs, atmospheric concentrations of the most-significant compounds have been declining. These substances are being gradually removed from the atmosphere; since peaking in 1994, the Effective Equivalent Chlorine (EECl) level in the atmosphere had dropped about 10 percent by 2008. The decrease in ozone-depleting chemicals has also been significantly affected by a decrease in [[bromine]]-containing chemicals. The data suggest that substantial natural sources exist for atmospheric [[methyl bromide]] ({{chem|CH|3|Br}}).<ref name=WMO-20Q /> The phase-out of CFCs means that [[nitrous oxide]] ({{chem|N|2|O}}), which is not covered by the Montreal Protocol, has become the most highly emitted ozone-depleting substance and is expected to remain so throughout the 21st century.<ref>{{cite web|url=http://www.noaanews.noaa.gov/stories2009/20090827_ozone.html |title=NOAA Study Shows Nitrous Oxide Now Top Ozone-Depleting Emission |publisher=Noaanews.noaa.gov |date=August 27, 2009 |access-date=April 6, 2011}}</ref>

According to the IPCC Sixth Assessment Report, global stratospheric ozone levels experienced rapid decline in the 1970s and 1980s and have since been increasing, but have not reached preindustrial levels. Although considerable variability is expected from year to year, including in polar regions where depletion is largest, the ozone layer is expected to continue recovering in coming decades due to declining ozone-depleting substance concentrations, assuming full compliance with the Montreal Protocol.<ref name="spm_ozone">{{Cite book |ref= {{harvid|IPCC AR6 WG1 Ch6|2021}}|chapter= Chapter 6: Short-lived climate forcers| last1 = Naik| first1 = Vaishali| last2 = Szopa| first2 = Sophie| last3 = Adhikary| first3 = Bhupesh| last4 = Artaxo Netto| first4 = Paulo Eduardo| last5 = Berntsen| first5 = Terje| last6 = Collins| first6 = William D.| last7 = Fuzzi| first7 = Sandro|chapter-url= https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter_06.pdf|display-authors=4|title= {{Harvnb|IPCC AR6 WG1|2021}}|year=2021}}</ref>

The Antarctic ozone hole is expected to continue for decades. Ozone concentrations in the lower stratosphere over Antarctica increased by 5–10 percent by 2020 and will return to pre-1980 levels by about 2060–2075. This is 10–25 years later than predicted in earlier assessments, because of revised estimates of atmospheric concentrations of ozone-depleting substances, including a larger predicted future usage in developing countries. Another factor that may prolong ozone depletion is the drawdown of nitrogen oxides from above the stratosphere due to changing wind patterns.<ref>{{Cite web |date=2007-12-09 |title=CNW Group {{!}} CANADIAN SPACE AGENCY {{!}} Canada's SCISAT satellite explains 2006 ozone-layer depletion |url=http://www.newswire.ca/en/releases/archive/October2006/06/c5891.html |access-date=2024-04-01 |archive-url=https://web.archive.org/web/20071209100943/http://www.newswire.ca/en/releases/archive/October2006/06/c5891.html |archive-date=2007-12-09 }}</ref> A gradual trend toward "healing" was reported in 2016.<ref name=healing/> In 2019, the ozone hole was at its smallest in the previous thirty years, due to the warmer polar stratosphere weakening the polar vortex.<ref>{{cite web | url =http://www.spacedaily.com/reports/Ozone_hole_set_to_close_999.html | title =Ozone hole set to close | date =12 November 2019 |website=Space Daily | publisher =Space Media Network | access-date =8 December 2019}}</ref> In September 2023, the Antarctic ozone hole was one of the largest on record, at 26 million square kilometers. The anomalously large ozone loss may have been a result of the [[2022 Hunga Tonga–Hunga Haʻapai eruption and tsunami|2022 Tonga volcanic eruption]].<ref>{{cite web|url=https://www.livescience.com/planet-earth/weather/one-of-the-biggest-on-record-ozone-hole-bigger-than-north-america-opens-above-antarctica|title='One of the biggest on record': Ozone hole bigger than North America opens above Antarctica|date=7 October 2023|access-date=10 October 2023|first=Harry|last=Baker|website=livescience.com}}</ref>
According to a 2023 United Nations assessment, the ozone layer is on track to recover to 1980 levels by around 2066 over Antarctica, by 2045 over the Arctic, and by 2040 for the rest of the world, assuming current regulations remain in place.<ref>{{cite web |title=Ozone layer recovery is on track, helping avoid global warming by 0.5°C |url=https://www.unep.org/news-and-stories/press-release/ozone-layer-recovery-track-helping-avoid-global-warming-05degc |publisher=UN Environment Programme (UNEP) |date=9 January 2023 |access-date=19 April 2025}}</ref>