9月16日「國際臭氧層保護日」當天，聯合國科學家表示，由於停用了包括冷煤與噴霧罐氣體等近100種會破壞臭氧層的物質，極地平流層上方幾個臭氧層的破洞已經停止擴大。 「過去數十年間，全球以及南北極上空的臭氧已不再減少，但也沒有增加」，臭氧層能夠保護地球以及地球上的居民免於來自太陽的紫外線傷害。
研究也指出，極區以外的臭氧層將在本世紀中葉恢復到1980年的水準，但是每年南極地區春季的臭氧層破洞，將需要比預期更長的時間來恢復。
逐步淘汰破壞臭氧層的化學物，是《蒙特婁議定書》的規定，這是一份為了保護平流層中的臭氧所訂定的國際性協議，在去年於全球已被普遍接受。
該報告證實蒙特婁議定書發揮了功用。這份報告於9月16日國際臭氧層保護日發表，以慶祝這份於1987年簽署的協議。
如果沒有蒙特婁議定書，「大氣中的破壞臭氧物質可能會在2050年以前增加10倍，」聯合國環境署執行主任史坦納(Achim Steiner)表示，「這可能導致超過2千萬人罹患皮膚癌，以及超過1.3億人罹患白內障，更不用說對人體免疫系統、野生動物以及農業生產所造成的傷害了。」
此外，蒙特婁議定書也「減少了氣候的變遷，而帶來了許多益處」，根據這份報告，許多破壞臭氧的物質也是潛在的溫室氣體。
另外一個重要的科學挑戰是依據對臭氧與氣候變遷之間複雜的關係的了解，來預測臭氧未來的濃度。
聯合國秘書長潘基文16日呼籲，蒙特樓協議是一個「非常好的典範」，設立了廣泛的框架與明確的目標，當政府有信心並且設定好開始的步驟後，以循序漸進的施行方法，來制定更遠大的目標。「當蒙特婁議定書與1987年簽定時，各國政府並沒有預想要淘汰任何有害臭氧的化學物質，」「然而全球各國強力的遵守協議，簽訂各國已經減少生產與使用這些有害的化學物質達到98%以上。」
世界氣象組織的秘書長亞羅(Michel Jarraud)說，「臭氧層的問題點出了對大氣層長期監測與研究的重要性，沒有這些研究，臭氧層所受到的破壞將有增無減，我們甚至無法在更多更嚴重的傷害發生前發現這件事。」 南極臭氧破洞是由英國科學家法爾曼(Joe Farman)、加德納(Brian Gardiner)與尚克林(Jonathan Shanklin)在1985年的英國南極調查時所發現。
報告中發現，現今在春季臭氧破洞變大時，南極仍有高量的紫外線輻射。
在禁止破壞臭氧的化學物質以及處理這些替代品所造成的傷害之間，有一個複雜的權衡關係。
許多破壞臭氧的化學物，例如曾用在冰箱與噴霧罐的氟氯碳化物(CFCs)，已經被淘汰。但是替代的物質像是氟氯烴(HCFCs)或是氟化烴(HFCs)則增加了，許多這類的物質的溫室效應都更加嚴重。
該報告預測，根據2007年蒙特婁議定書的協議內容，氟氯烴的排放總量將未來10年內開始下降，但是現在增加的速度卻比四年前更快。
其中數量最多的HCFC-22在2007-2008年間的增加幅度比2003-2004年間的速度要快50%。
根據這份報告，HCFs的數量與排放量正以每年8%的速度增加。HFC-23是HCFC-22生產過程中的一種副產品，它雖然對臭氧層沒有影響，但其溫室效應卻是二氧化碳(現在最多的一種溫室氣體)的14000倍之多。大多數氣候科學家均同意，地球增溫的幅度必須低於攝氏2度，以避免氣候變遷最糟的後果-海平面上升、物種滅絕、極端氣候事件、風暴、洪水以及乾旱。
「蒙特婁議定書是科學家與決策者之間共同合作的一個非常好的例子，成功緩解了環境與社會面臨的嚴重威脅。」世界氣象組織秘書長亞羅說，「人類活動將繼續改變大氣的成份，世界氣象組織的全球大氣監測計畫將繼續進行這些重要的監測、研究以及評估，以提供了解並預測在區域和全球尺度下，氣候變遷所需的科學數據。」
The ozone holes high in the stratosphere over each of the polar regions have stopped growing due to the phase out of nearly 100 ozone-depleting substances once used in products like refrigerators and spray cans, United Nations scientists said today in a new report.
"Over the past decade, global ozone and ozone in the Arctic and Antarctic regions is no longer decreasing but is not yet increasing," the study finds. The ozone layer protects Earth and its inhabitants from the harmful ultraviolet rays of the Sun.
The ozone layer outside the polar regions will recover to pre-1980 levels before the middle of this century, but the annual springtime ozone hole over the Antarctic is expected to take much longer, the study projects.
The phase out of ozone-destroying chemicals is required under the Montreal Protocol on Substances That Deplete the Ozone Layer, an international agreement written to protect the stratospheric ozone layer, which last year achieved universal ratification.
The report confirms that the Montreal Protocol is working. It was published on September 16, the annual International Day for the Preservation of the Ozone Layer, to mark protocol's signature date in 1987.
"Atmospheric levels of ozone-depleting substances could have increased tenfold by 2050," without the Montreal Protocol, said UNEP Executive Director Achim Steiner.
"This in turn could have led to up to 20 million more cases of skin cancer and 130 million more cases of eye cataracts, not to speak of damage to human immune systems, wildlife and agriculture," Steiner said.
The Montreal Protocol has "provided substantial co-benefits by reducing climate change," because many substances that deplete the ozone layer are also potent greenhouse gases, according to the report.
An important remaining scientific challenge is to project future ozone abundance based on an understanding of the complex linkages between ozone and climate change.
UN Secretary-General Ban Ki-moon today called the Montreal Protocol "an excellent example" of setting a broad framework, clear targets and a gradual approach to implementation as governments gain confidence and build on initial steps, setting more ambitious goals.
"When the Montreal Protocol was signed in 1987, governments did not originally envision the phase-out of any ozone-depleting substance," said Ban. "Yet, as a result of strong national and global compliance, parties to the Montreal Protocol have cut production and consumption of these harmful chemicals by more than 98 percent."
Michel Jarraud, secretary-general of the World Meteorological Organization, WMO, said, "The ozone-hole issue demonstrates the importance of long-term atmospheric monitoring and research, without which ozone destruction would have continued unabated and might not have been detected until more serious damage was evident."
The Antarctic ozone hole was discovered in 1985 by British scientists Joe Farman, Brian Gardiner, and Jonathan Shanklin of the British Antarctic Survey.
In Antarctica today, high levels of ultraviolet radiation continue to be seen when the springtime ozone hole is large, the report finds.
There is a complex trade-off between banning ozone depleters and dealing with the harm caused by their replacements.
Many ozone depleting chemicals, such as CFCs, chlorofluorocarbons, once present in products such as refrigerators and spray cans, have been phased out.
But demand for replacement substances called HCFCs, hydrochlorofluorocarbons, and HFCs, hydrofluorocarbons, has increased. Many of these are powerful greenhouse gases.
The report projects that total emissions of HCFCs will begin to decline in the coming decade due to measures agreed under the Montreal Protocol in 2007. But they are currently increasing faster than four years ago.
The most abundant one, HCFC-22, increased more than 50 percent faster in 2007-2008 than it did in 2003-2004.
Abundances and emissions of HFCs currently are increasing at about eight percent per year, according to the report.
HFC-23 is a byproduct of HCFC-22 production. Although it has no impact on the ozone layer it is more than 14,000 times more powerful as a climate-warming greenhouse gas than carbon dioxide, the most abundant greenhouse gas.
Most climate scientists agree that keeping the global temperature rise to under 2 degrees Celsius is essential to averting the worst consequences of climate change - rising sea levels, extinction of species, extreme weather events, storms, floods, and droughts.
"The Montreal Protocol is an outstanding example of collaboration among scientists and decision-makers that has resulted in the successful mitigation of a serious environmental and societal threat," said WMO chief Jarraud.
"Human activities will continue to change the composition of the atmosphere," said Jarraud. "WMO's Global Atmosphere Watch program will therefore continue its crucial monitoring, research and assessment activities to provide scientific data needed to understand and ultimately predict environmental changes on both regional and global scales."
