Diapositiva 1
DI LÀ DAI LIMITI E RITORNO:
LA STORIA DELL’OZONO
“Siamo coinvolti, in un modo o nell'altro, in un esperimento su larga scala volto a
cambiare la composizione chimica dell'atmosfera, ma non abbiamo alcuna chiara
nozione di quelle che potranno essere le sue conseguenze biologiche o
meteorologiche”
F. SHERWOOD ROWLAND, 1986
Chlorofluorocarbons (CFCs) and other ozone-depleting substances (ODS) include a range of
industrial chemicals first developed in the 1920s.
They are stable and nontoxic, cheap to produce, easy to store and highly versatile.
As a result, they came to be used in a wide range of applications, including as coolants for
refrigeration and air conditioning, for blowing foams, as solvents, sterilants and propellants for
spray cans.
When released, they rise into the stratosphere, where they are broken apart by solar radiation to
release chlorine or bromine atoms, which in turn destroy ozone molecules in the protective
stratospheric ozone layer.
They are slow to disappear, which means the emissions of yesterday and today will contribute to
ozone depletion for years to come.
Diapositiva 2
Schematizzazione della stratificazione atmosferica
con individuazione della fascia di ozono
Il livello dello strato d’ozono presente nell’atmosfera viene costantemente misurato.
La marcata diminuzione di ozono stratosferico, in particolare nella stratosfera antartica, è legata
all’emissione di composti artificiali quali gli idrocarburi alogenati, tra cui i più dannosi sono i
clorofluorocarburi (CFC), usati prevalentemente negli impianti di refrigerazione, come propellente
nelle bombolette spray, nell’industria elettronica, per la preparazione di vernici e solventi, nella
produzione di alcune plastiche e in alcuni processi industriali.
Gli enormi quantitativi di CFC e halon già prodotti e contenuti in impianti e apparecchiature in uso,
costituiscono una minaccia per la fascia di ozono stratosferico.
Una valida alternativa tecnica all’uso di queste sostanze è l’impiego degli idroclorofluorocarburi
(HCFC), che hanno un potenziale di distruzione dell’ozono basso più.
Diapositiva 3
Variation of temperature
(bottom axis) and ozone (top
axis) with altitude from the
surface of the Earth.
In
the
troposphere,
temperature decreases with
altitude.
In
the
stratosphere,
temperature increases with
altitude.
The tropopause is located at
the minimum temperature.
Ozone
concentrations
maximize
in
the
stratosphere.
The ozone concentration is
shown on a log scale in units
of the number of molecules
per cubic cm (#/cm3).
On the basis of temperature, the atmosphere is subdivided into different altitude regions like the
layers of an onion.
Closest to the Earth’s surface is the region called the troposphere. This region includes the air that
we breathe and is where weather systems occur.
The air pressure (and also the total number of molecules per unit volume) decreases almost
exponentially with altitude so that roughly 90% of the mass of the atmosphere is in the
troposphere and 50% of the mass is within the 5.5 km closest to the Earth.
Above the troposphere the temperature begins to increase as the altitude increases. This is due to
the absorption of light energy by ozone.
The altitude where the lowest temperatures occur in the lower atmosphere defines the top of the
troposphere and is called the tropopause; above that is the region called the stratosphere.
Because the stratosphere is a giant inversion layer with warm air above cold air, there is very slow
vertical mixing in this region.
In very broad terms, the global atmospheric circulation consists of upwelling into the stratosphere
near the equator and downward transport of stratospheric air near the poles.
The tropopause height is 16–18 km near the equator and 8–12 km near the poles.
Ozone concentrations reach a maximum in the stratosphere, forming the so-called ozone layer.
Diapositiva 4
Although ozone is a vital component of the stratosphere, the actual
amount of ozone is very small. If all of the ozone in the atmosphere
were compressed to the pressure at sea level, the ozone would form a
layer only 3 mm thick, compared with 8,500 m if the entire atmosphere
were similarly compressed.
Many of the molecules released on Earth do not reach the stratosphere
because they are soluble (can dissolve) in water and return to the
surface in precipitation or are broken down by chemical reactions in
the troposphere.
The only molecules that do reach the stratosphere are those that are
insoluble in water and also are chemically inert (or unreactive). A
partial list of these compounds includes nitrous oxide (N2O), carbonyl
sulfide (OCS), methane (CH4), chlorofluorocarbons (CFCs), and halons
(carbon-based molecules containing bromine).
Some of these species are natural and some are anthropogenic
(generated by human activity). Although these molecules do not react
in the troposphere, when they reach the stratosphere they absorb UV
light and break apart. Such reactions in which molecules absorb light
and fall apart are called photolysis (or photochemical) reactions.
The photolysis of these molecules in the stratosphere affects ozone
concentrations.
Diapositiva 5
Diapositiva 6
OZONE: GOOD UP HIGH, BAD NEARBY
Ozone is a gas that occurs both in the Earth’s upper
atmosphere (the stratosphere) and at ground level.
Ozone can be “good” or “bad” for people’s health and
the environment, depending on its location in the
atmosphere.
“Good” ozone is produced naturally in the stratosphere
and is “good” because it blocks harmful UV radiation
from reaching the Earth’s surface where it can harm
people and ecosystems.
“Bad” ozone is an air pollutant found at ground level and
is “bad” because it is harmful to breathe and can damage
crops, trees, and other vegetation.
Ground-level ozone is a main component of urban smog.
Diapositiva 7
Wavelength regions of ultraviolet and visible light
Diapositiva 8
We care about ozone depletion because a thinner
ozone layer allows more UV radiation to reach the
Earth’s surface.
Overexposure to UV radiation can cause a range of
health effects, including skin damage (skin cancers
and premature aging), eye damage (including
cataracts), and suppression of the immune system.
Researchers believe that overexposure to UV
radiation is contributing to an increase in melanoma,
the most fatal of all skin cancers.
Diapositiva 9
UV radiation can damage sensitive crops, such as
soybeans, and reduce crop yields.
Some scientists believe that marine phytoplankton,
which serve as the base of the ocean food chain, are
already under stress from UV radiation.
This stress could have profound effects on the food
chain and on food productivity.
Additionally, since most ozone-depleting substances
are also potent greenhouse gases, replacing these
substances with alternatives that are safer for the
ozone layer can also reduce greenhouse gas
emissions and slow climate change.
Diapositiva 10
The impact of local air pollution on the growth of
wheat in suburban Lahore, Pakistan
The plants in the centre and on the right were
both grown in local air, while the plant on the
left was grown in filtered air.
The effect of filtering the polluted air
increased grain yield by
about 40 per cent.
Diapositiva 11
Melanin
Dark pigment in skin for protection against UV radiation.
Developed originally in populations living under intense UV
radiation in equatorial Africa.
Populations that migrated to higher latitudes became lighter
due to natural selection since some UV is needed to
produce vitamin D in the skin, and dark pigmentation
blocks the little UV available at higher latitudes for vitamin
D production. Vitamin D necessary to prevent bone
fractures, bow legs, slow growth (rickets).
As populations moved across Asia to North America and
down toward equatorial South America, production of
melanin again became an advantage
Lighter skin color in equatorial South America than in
equatorial Africa due to shorter presence of population in
South America
Diapositiva 12
UV Effects on the Skin
Sunburn (erythema)
Skin reddening, blisters
Photoaging (accelerated aging of skin)
Loss of skin elasticity, wrinkles, altered pigmentation, decrease
in collagen
Diapositiva 13
Skin Cancer
Basal-cell carcinoma (BCC) (79%)
Tumor develops in basal cells, deep in skin
Grows through skin and scabs
Doesn’t spread; removable by surgery, radiation, rarely fatal
Squamous-cell carcinoma (SCC) (19%)
Tumor develops in squamous cells, outside of skin
Appears as red mark
Spreads but removable by surgery, radiation, rarely fatal
Cutaneous melanoma (CM) (2%)
Dark-pigmented malignant tumor arising in melanocyte cell
Spread quickly; fatal in 1/3 of cases
CM as common as SCC in Northern Europe
Skin cancer rates increase from Equator to poles
Relatively high cancer rates in Australia/New Zealand
Lifetime exposure to UV not necessary to obtain skin cancer
Diapositiva 14
UV Effects on the Eye
Snowblindness
Inflammation or reddening of the eyeball
Cataract
Loss in transparency of the lens
Blindness unless lens removed
Ocular melanoma
Cancer of iris and related tissues
Diapositiva 15
Other UV Effects
Immune system effects
Reduces ability to fight disease and tumors
Effects on microorganisms (e.g., phytoplankton), animals, plants
Effects on global carbon and nitrogen cycles
Damage to phytoplankton reduces CO2(g) uptake
UV-B enhances photodegradation of plants, increasing CO2(g)
UV-B affects rate of nitrogen fixation by cyanobacteria
Effects on tropospheric ozone
Enhanced UV-B increases tropospheric ozone
Enhanced absorbing aerosols reduce UV-B, reducing ozone
Diapositiva 16
Major Absorbers of UV Radiation at
Different Altitudes
Wavelengths Dominant
(mm)
Absorbers
0.01-0.25
N2
O2
Location of
Absorption
Thermosphere
Thermosphere
Near-UV
UV-C
UV-B
0.25-0.29
0.29-0.32
O3
O3
UV-A
0.32-0.38
Particles
NO2
Particles
Stratosphere
Stratosphere
Troposphere
Polluted troposphere
Polluted troposphere
Polluted troposphere
Spectrum
Far-UV
Diapositiva 17
The ozone absorption spectrum showing where ozone filters UV
radiation.
The large absorption band of ozone between 200 and 300 nm is
called the Hartley band, named after its discoverer, John Hartley.
Ozone absorbs UV radiation (wavelengths, λ, between 200 and 300 nm) preventing high intensities
at these wavelengths from reaching the ground.
Diapositiva 18
ASSORBIMENTO DELLA LUCE NELL’ATMOSFERA
La radiazione ultravioletta emessa dal Sole è assorbita quasi totalmente dall'ossigeno e dall'ozono
presenti nell'atmosfera.
L’ozono, in particolare, assorbe la radiazione solare nella cosiddetta banda UVB, pericolosa per gli
esseri viventi.
Diapositiva 19
La radiazione solare che riesce ad arrivare sulla Terra è composta da radiazioni elettromagnetiche che hanno
lunghezze d’onda corte comprese nello spettro che va da 100 a 800nm. La componente ultravioletta della
radiazione solare viene suddivisa in UVC, UVB e UVA che hanno lunghezze d’onda diverse; l’ozono stratosferico
assorbe completamente gli UVC di lunghezza d’onda compresa tra 100 e 280nm, per il 95% gli UVB di lunghezza
d’onda compresa tra 280 e 315nm ed appena per il 5% gli UVA con lunghezza d’onda compresa tra 315-400nm.
Diapositiva 20
How life evolved on Earth
The oxygen produced by underwater plants eventually
accumulated in the atmosphere.
When UV light broke apart the oxygen, ozone was formed.
After the ozone layer was formed, UV light was prevented from
reaching the ground.
Then, plants and animals could exist on the surface of the planet.
Diapositiva 21
If less ozone is present in the stratosphere, less UV light is
absorbed there, so more reaches the ground.
An increase in UV radiation has been observed as a function of
decreasing ozone concentrations.
Diapositiva 22
IL CLORO REATTIVO AUMENTA, L’OZONO
ANTARTICO DIMINUISCE
Gli strumenti a bordo dell'aereo di ricerca ER-2, della NASA, hanno misurato simultaneamente le
concentrazioni di monossido di cloro e di ozono mentre l'aereo volava da Punta Arenas, in Cile (53°
S), fino a 72° S.
I dati mostrati sopra sono stati raccolti il 16 settembre 1987. Quando l'aereo entrò nel buco
nell'ozono, la concentrazione di monossido di cloro crebbe fino a molte volte i livelli normali,
mentre i livelli di ozono diminuivano rapidamente.
Questo risultato ha contribuito a dimostrare che il buco nell'ozono è provocato da inquinanti
contenenti cloro.
Diapositiva 23
In the 1970s, chemists Sherwood Rowland and Mario Molina discovered that CFCs contribute to
ozone depletion.
The two collaborators theorized that CFC gases react with solar radiation and decompose in the
stratosphere, releasing chlorine atoms that are able to destroy large numbers of ozone molecules.
Their research was first published in Nature magazine in 1974.
The National Academy of Sciences concurred with their findings in 1976, and in 1978 CFCbased
aerosols were banned in the United States.
Further validation of their work came in 1985 with the discovery of the ozone hole over
Antarctica.
In 1995, the two chemists shared the Nobel Prize for Chemistry with Paul Crutzen, a Dutch
chemist who demonstrated that chemical compounds of nitrogen oxides accelerate the
destruction of stratospheric ozone.
Diapositiva 24
The ozone layer acts like a shield in the upper atmosphere (the stratosphere), to protect life on
Earth from harmful ultraviolet (UV) radiation.
In 1974, scientists discovered that emissions of chlorofluorocarbons, or CFCs, were depleting ozone
in the stratosphere.
CFCs were a common aerosol propellant in spray cans and were also used as refrigerants, solvents,
and foam-blowing agents.
In the 1980s, scientists observed a thinning of the ozone layer over Antarctica, and people began
thinking of it as an “ozone hole.”
Additional research has shown that ozone depletion occurs over every continent.
As our scientific knowledge about ozone depletion grew, so too did the response to the issue.
In 1987, leaders from many countries came together to sign a landmark environmental treaty, the
Montreal Protocol on Substances That Deplete the Ozone Layer.
Today, more than 190 countries—including the United States—have ratified the treaty.
These countries are committed to taking action to reduce the production and use of CFCs and
other ozone-depleting substances to protect the ozone layer.
Countries are phasing out the production and consumption of ozone-depleting substances in
groups, focusing on those chemicals with the most ozone-depleting potential first, followed by
those that pose the next greatest ozone-depletion risk (“first-generation” and “secondgeneration” substances).
Diapositiva 25
PRODUZIONE MONDIALE DI
CLOROFLUOROCARBURI
La produzione di clorofluorocarburi (CFC) crebbe rapidamente fino al 1974, data di pubblicazione
dei primi articoli nei quali veniva ipotizzato che questi potessero distruggere lo strato di ozono
stratosferico.
La successiva diminuzione si spiega con la lotta degli ambientalisti contro le bombolette spray per
aerosol
contenenti CFC, che negli Stati Uniti furono messe al bando nel 1978.
Dopo il 1982, a causa dell'incremento di altri impieghi dei CFC, la produzione aumentò ancora per
alcuni anni.
Cominciò a diminuire nel 1990, allorché, in attuazione di accordi internazionali, venne avviata
l'eliminazione graduale dei CFC.
Gli HCFC (idroclorofluorocarburi) sono ancore ammessi in sostituzione di altre sostanze; la graduale
eliminazione di questa classe di composti chimici dovrebbe giungere a termine tra il 2030 e il 2040.
Diapositiva 26
CFC Emission Since the 1930s
Release (1000 metric tonnes/yr)
500
CFC-12
400
300
200
100
CFC-11
CFC-113
HCFC-22
HCFC-141b
HFC-134a
0
1930 1940 1950 1960 1970 1980 1990 2000
Year
Diapositiva 27
Since the 1950s, CFCs have been used in refrigerators, in aerosol spray cans, as cleaning solvents,
and as foam-blowing agents. After Molina and Rowland showed in the 1970s that chlorine from
CFCs could destroy ozone, CFC use in spray cans (aerosols) for hairspray, deodorant, and paint was
restricted in the United States, Canada, Norway, and Sweden.
Figure shows how this ban affected worldwide CFC production and consumption.
Overall, the production of CFCs has steadily increased from the 1960s to the mid-1980s except for
the ten year period directly after CFCs in aerosols were banned.
The consumption pie charts show that the relative usage of CFCs in aerosols decreased between
1974 and 1988.
However, usage for other applications continued to rise after aerosol usage dwindled, causing the
overall production rate to climb during the 1980s.
This is an example of poor regulations as the use of CFCs in aerosols was restricted instead of the
CFCs.
Diapositiva 28
Chlorine Emission to Stratosphere
Chemical
Percent emission to stratosphere
Anthropogenic sources
CFC-12 (CF2Cl2)
CFC-11 (CFCl3)
Carbon tetrachloride (CCl4)
Methyl chloroform(CH3CCl3)
CFC-113 (CFCl2CF2Cl)
HCFC-22 (CF2ClH)
28
23
12
10
6
3
Natural sources
Methyl chloride (CH3Cl)
Hydrochloric acid (HCl)
15
3
Total
100
Diapositiva 29
Produzione nazionale di sostanze lesive per l’ozono
stratosferico (CFCs, CCl4, HCFCs)
Trend decrescente fino ad annullarsi nel 2005, in linea con gli obiettivi fissati dalla
normativa, che individua nel 31/12/08 il termine ultimo per la produzione, l'utilizzazione,
la commercializzazione, l'importazione e l'esportazione delle sostanze lesive per l'ozono.
Il Protocollo di Montreal, reso esecutivo dal Parlamento italiano con L 393/88, impegna le parti
firmatarie a stabilizzare, ridurre e bandire le produzioni e i consumi delle sostanze lesive per
l'ozono secondo uno schema articolato per obiettivi e scadenze temporali.
In Italia, la L 549/93 con le successive modifiche, tra cui la L 179/97, in adeguamento al
Regolamento CE 3093/94, stabilisce le modalità di riduzione e successiva cessazione d'uso delle
sostanze lesive per l'ozono.
In particolare la L 179/02 (che nell'articolo 15 modifica la L 549/93) impone come termine ultimo il
31/12/08 per la produzione, l'utilizzazione, la commercializzazione, l'importazione e l'esportazione
delle sostanze lesive per l'ozono.
Diapositiva 30
Protecting the ozone layer has enormous benefits for all countries because stratospheric ozone
depletion is a global issue.
All parts of our daily lives have been touched by ozone-depleting substances.
Prior to the 1980s, CFCs and other ozone-depleting substances were pervasive in modern life.
But thanks to the work of individuals, businesses, organizations, and governments around the
world, substitutes that are safer for the ozone layer continue to be developed for many ozonedepleting substances.
Every dollar invested in ozone protection provides $20 of societal health benefits in the United
States.
Efforts to protect the stratospheric ozone layer will produce an estimated $4.2 trillion in societal
health benefits in the United States over the period 1990 to 2165.
Diapositiva 31
Diapositiva 32
MISURAZIONI DELL’OZONO A HALLEY, IN
ANTARTIDE
La concentrazione di ozono nell'atmosfera sopra Halley, in Antartide, misurata nel mese di ottobre
quando, con la primavera australe, ritorna il Sole, è andata riducendosi per più di un decennio
prima che nel 1985 fosse pubblicato l'articolo con l'annuncio del buco nell'ozono.
Da allora, la concentrazione di ozono misurata ogni ottobre ha continuato a diminuire.
Diapositiva 33
Size of the Antarctic ozone hole over time
The area under the ozone hole varies from year to year, and it is not yet possible to say whether it
has hit its peak.
The largest “holes” occurred in 2000, 2003 and 2006. On 25 September 2006, it extended over 29
million
square kilometres and the total ozone loss was the largest on record.
Chemistry climate models predict that recovery to pre-1980 Antarctic ozone levels can be expected
around 2060–2075.
Diapositiva 34
Ozone hole area (106 km2)
Ozone minimum (Dobson units)
Change in Size of Antarctic Ozone Hole
Diapositiva 35
Regulation of CFCs
June 1974: Effects of CFCs on ozone hypothesized by Rowland &
Molina
Dec. 1974: Bill to study, regulate CFCs killed in U.S. Congress
1975: Congress sets up committee to study CFC effects
1976: U.S. National Academy of Sciences releases report suggesting
long-term damage to ozone layer due to CFCs
1976: On basis of report, U.S Food and Drug Administration,
Environmental Protection Agency, Consumer Product Safety
Commission recommend phase out of spray cans in the U.S.
Oct. 1978: Manufacture/sale of CFCs for spray cans banned in U.S.
The growing use of CFCs and the hypothesis that CFCs cause ozone depletion prompted many
nations of the world to sign the Vienna Convention for the Protection of the Ozone Layer in 1985.
Although the Vienna Convention did not include explicit restrictions on CFCs, it called for future
regulatory actions and scientific understanding of the ozone layer, CFCs, and halons.
More importantly, it recognized that ozone depletion was an international issue and that the policy
questions it raised would be resolved by the international community.
Thus, it set the stage and provided the framework for the Montreal Protocol of 1987.
Furthermore, it was prepared before the discovery of the ozone hole and, in fact, before any ozone
loss was observed in the “real” atmosphere.
Following the framework of the Vienna Convention, the discovery of the ozone hole led to the
formation of the Montreal Protocol on
Substances That Deplete the Ozone Layer, which officially limited the production and use of CFCs.
The countries that signed the original document in 1987 agreed to freeze CFC production and use
at the 1986 rates by the year 1989, and to cut CFC production and use by 50% over the next ten
years.
After the protocol was adopted, it was determined that the rates proposed for CFC reduction were
not rapid enough to substantially decrease the chlorine loading of the atmosphere.
Diapositiva 36
Regulation of CFCs
1980: U.S. EPA proposes limiting emission of CFCs from
refrigeration, but proposal rebuffed
1985: Vienna Convention.Initially 20 countries obligated to reduce
CFCs
1987: Montreal Protocol. Initially 27 countries agreed to limit CFCs
and Halons.
1990: London Amendments
1997: Copenhagen Amendments
In fact, under the original protocol that was established in Montreal in 1987, chlorine levels would
still be increasing by the end of the 21st century.
Research continued, and the scientific understanding of ozone depletion progressed.
Detailed model calculations showed that if the CFCs were phased out four years earlier, the time
for chlorine concentrations to return to pre–ozone hole levels would be reduced by 20 years.
Furthermore, in the winter of 1991/92, scientists who were monitoring ozone loss above the Arctic
reported to the public the presence of unusually high amounts of ClO over the northern high- to
midlatitudes.
Fortunately, the winter did not remain cold enough for the active chlorine to replenish itself via
heterogeneous reactions.
The predictions that chlorine concentrations could be more rapidly returned to pre–ozone hole
levels coupled with the immediate possibility of ozone loss over populated regions prompted the
addition of the Copenhagen amendments in 1992.
These amendments provided for the complete phaseout of CFCs, carbon tetrachloride, and methyl
chloroform by the year 1996. Furthermore, hydrochlorofluorocarbons (HCFCs), which were being
developed to temporarily replace CFCs, were added to the list for phaseout by the year 2030
because they also contained chlorine that could destroy ozone.
Diapositiva 37
Phaseout Schedule of CFCs
Year
Montreal London U.S. Clean Copenhagen Eur. Com.
Protocol Amend. Amend.
Amend.
Schedule
(1987)
(1990) (1990)
(1992)
(1994)
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
100
100
100
80
80
80
80
80
80
50
50
100
100
80
80
50
50
15
15
15
0
85
80
75
25
25
0
25
25
0
50
15
0
Since HCFCs react in the troposphere with OH, most HCFCs do not reach the stratosphere intact
like the CFCs.
Therefore, the threat to the ozone layer is not as serious from HCFCs as it is from CFCs.
Finally, these amendments recognized the potential for the bromine-containing compound methyl
bromide, used widely as a fumigant, to destroy ozone.
Diapositiva 38
CRESCITA PREVISTA DELLE CONCENTRAZIONI
DI CLORO E BROMO INORGANICI NELLA
STRATOSFERA A CAUSA DELLE EMISSIONI DI CFC
La figura mostra le abbondanze di cloro e bromo nella stratosfera misurate in passato e previste in
futuro a seconda delle politiche adottate:
•nessun protocollo;
•misure previste dal primo Protocollo di Montreal;
•accordi aggiuntivi stipulati successivamente.
Con un tasso di produzione di CFC pari a quello del 1986, la concentrazione di cloro nella
stratosfera sarebbe aumentata di un fattore 8 nel 20-50. Il primo Protocollo di Montreal fissava
tassi di emissione più modesti, ma sufficienti a far crescere i livelli di cloro in modo esponenziale.
L’accordo di Londra bandiva la maggior parte degli impieghi di CFC, ma non tutti; in tal modo, i
livelli di cloro avrebbero ugualmente cominciato ad aumentare attorno al 2050.
Gli accordi successivi hanno rafforzato le restrizioni sugli impieghi delle sostanze chimiche in grado
di liberare cloro; secondo le proiezioni, ciò dovrebbe portare a una diminuzione dei livelli di cloro
nella stratosfera dopo l'anno 2000.
Diapositiva 39
Effect of international agreements on the
predicted abundance of ODS in the
stratosphere
Diapositiva 40
Global Ozone Depletion and Recovery
Sustained recovery of the ozone layer will require worldwide phaseout of ozone-depleting
substances
The ozone layer has not grown thinner since 1998 over most of the world, and it appears to be
recovering because of reduced emissions of ozone-depleting substances.
Antarctic ozone is projected to return to pre-1980 levels by 2060 to 2075.
Diapositiva 41
The Impact of OzoneDepleting Substances on
Climate Change
Diapositiva 42
Diapositiva 43
Common Ozone-Depleting Substances and Some Alternatives‡
The phaseout of ozone-depleting substances has also made a substantial contribution toward the
reduction in greenhouse gas emissions since their global warming potential is very high.
Diapositiva 44
Phasing out ozone-depleting substances has already
reduced greenhouse gas emissions by more than 8,900
million metric tons of carbon equivalent (MMTCE) per
year—equivalent to the cumulative carbon dioxide
emissions associated with …
Generating enough electricity to power every U.S. home
for more than 13 years ...
and
Preserving 89 million acres of forests from
deforestation—more than twice the size of Florida ...
and
Saving more than 1.2 trillion gallons of gas—enough to
make 4.8 billion round trips from New York to Los
Angeles by car.
Diapositiva 45
This graph illustrates the projected annual greenhouse gas emissions (measured in million metric
tons of carbon equivalent) that will be avoided as a result of both the U.S. phaseout of HCFCs and
the improved management of refrigerant emissions.
Diapositiva 46
Ratification of major multilateral
environmental agreements