Fall! 992 Mo.2
On Owr Changing Planet
Our
Ozone
Shield
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[UK fH'COHU' ck'dr to scientists and to governments
dlikv thai hitman acfirities are threatening our ozone
afntid. Behind (bis environmental problem lies a tale
ofluin challenges; the scientific quest to understand
unr fCf»w> shield and the debate among governments
mvrbow to Iwsl ptvtect it. Here is the story.
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Our
Ozone
\
0:ONE AND HUMANKIND. For nearly a billion years, ozone molecules
in the atmosphere have safeguarded life on this planet. But
over the past half century., humans have placed the ozone
layer in jeopardy. We have unwittingly polluted the air with
chemicals that threaten to eat away the life-protecting shield
surrounding our world.
Although ozone molecules play such a vital role in the atmosphere,
they are exceedingly rare, in every million molecules of air, fewer than
t - ^
ten are ozone. Nitrogen and oxygen make up the vast proportion of
the molecules in the air we breathe. In this way, ozone resembles a
critical spice in a pot of soup. Using just a few grains of a particular
herb, a chef can season the whole pot with a distinctive flavor, g]
Ozone molecules show different character traits depending on
" where they exist in the atmosphere. About 90 percent of the ozone
resides in a layer between 10 and 40 kilometers (6 and 25 miles) above
the Earth's surface in a region of the atmosphere called the strato-
sphere. Ozone there plays a beneficial role by absorbing dangerous
ultraviolet radiation from the sun. This is the ozone threatened by some
of the chemical pollutants that we have released into the atmosphere.
Close to the planet's surface, however, ozone displays a destructive
side. Because it reacts strongly with other molecules, it can severely
(damage the living tissue of plants and animals. Low-lying ozone is a
:ey component of the smog that hangs over many major cities across
world, and governments are attempting to decrease its levels.
Ozdhejn the region below the stratosphere—called the troposphere—
qan alsoxjontribute to greenhouse warming.
Re'ports to the Mation ^ Fa/11992
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Water Vapor -
Methane
Although smog ozone and stratospheric ozone
are the same molecule, they represent separate
environmental issues, controlled by different forces
in the atmosphere. This monograph- will focus on
the stratospheric ozone layer and the world's
attempts to protect it.
What is ozone and where does it originate? The
term itself comes from the Greek word meaning
"smell," a reference to ozone's distinctively pungent
odor. Each molecule contains three oxygen atoms
bonded together in the shape of a wide triangle. In
the stratosphere, new ozone molecules are con-
stantly created in chemical reactions fueled by
power from the sun. £$•]
The recipe for making ozone starts off with
oxygen molecules (O2). When struck by the
sun's rays, the molecules split apart into single
oxygen atoms (O), which are exceedingly
reactive. Within a fraction of a second,
the atoms bond with nearby oxygen
molecules to form triatomic mol-.
ecules of ozone (O3).
Solar rays
m*k* ozona
Hydrogen
Nitrous Oxide
Other
, Even as the sun's energy produces new ozone,
these gas molecules are continuously destroyed by
natural compounds containing nitrogen, hydrogen,
and chlorine. Such chemicals were all present in
the stratosphere—in small amounts—long before
humans began polluting the air. Nitrogen comes
from soils and the oceans, hydrogen comes
mainly from atmospheric water yapor, and chlo-
rine comes from the oceans.
The stratospheric concentration of ozone there-
'• . ',-''' ' ' t • •** •
fore represents a balance,, established over the'
aeons, between creative and destructive forces.
The total level of ozone in the stratosphere remains
fairly constant, an arrangement resembling a tank
with open drains. As long as the amount of water
pouring in equals the-amount flowing but the drain
holes, the water level in the tank stays the same.
In the stratosphere, the concentration of ozone
does vary slightly, reflecting small shifts in the
balance between creation and destruction. 'These
fluctuations result from many natural processes
such as the seasonal cycle, volcanic eruptions, and
changes in the sun's intensity. , . -
- For about a billion years, the natural ozone
, system worked smoothly, put now human
beings have upset the delicate, balance.
By polluting the atmosphere with ad-
ditional chlorine-containing chemi-
Reactive nitrogen
destroys ozone.
Reactive chtotme
destroys ozone
Reactive hydrogen
destroys ozqne
The amount, of ozone in the Earth's stratosphere is a balance
between continuous production and loss. Ozone is produced by
the sun's rays. It is removed by chemical reactions. But humans
- have added to the amount.of reactive chlorine compounds in the
stratosphere. Since the loss of ozone is how greater than the
production of ozone, we are thinning our prbtective'shield.
Reports to the Nation -Fall 1992
-------
Holv
does such a
a huge role?
cals, we have enhanced the forces that destroy
ozone—a situation that leads to lower ozone
concentrations in the stratosphere. The addition of
these chemicals is, the same as drilling a larger
"chlorine" drain in the tank, causing the level to
drop.
A Problem Arises: The Early 1970s
No one dreamed human activity would threaten
the ozone layer until the early to mid-1970s, when
scientists discovered two potential problems: ultra-
fast passenger planes and spray cans, g
The plane threat surfaced first, after the inven-
tion of a new breed of commercial aircraft called
supersonic transport (SST) These planes could fly
faster than the speed of sound and promised to
trim hours off long journeys. In the 1970s, the
United States and other nations began considering
whether to build large fleets of such ultrafast jets
As scientists such as Harold Johnston and Paul
Crutzen looked at the SST issue, they grew
concerned about the effects such planes might
have on the stratosphere. SSTs are unusual
because they must fly high up in the atmo-
sphere—where the air is thin—to achieve
their fast speeds. Several researchers
suspected that the reactive nitrogen
compounds from SST exhaust might
Most of the Earth's ozone.is high in the upper .part of'the
'atmosphere—the stratosphere,:This "good" ozone serves
as Our shieid_against incoming solar ultraviolet'radiation.
The "bad'' ozone in the lower part of Jhe atmosphere—
the troposphere—adds"to greenhpusewarmingand'
is a majorpart of smog jn cities.
accelerate the natural chemical destruction of
ozone, causing ozone levels to drop.
In 1974, news of another possible threat to the
ozone layer made national headlines. This time
scientists implicated a widely used class of chemi-
cals known as chlorofluorocarbons (CFCs), which
were most commonly known as the aerosol propel-
lant in spray cans. Invented in the late 1920s, CFCs
contain chlorine, fluorine, and carbon atoms ar-
ranged in an extremely stable structure.
j
Through decades of use, CFCs proved
themselves to be ideal compounds for many
purposes. They are nontoxic, noncorrosive,
nonflammable, and unreactive with most other
substances. Because of their special properties,
they make excellent coolants for refrigerators
and air conditioners. CFCs also trap heat well, so
manufacturers put them into foam
-------
;$&'$ I ;' products such as cups and insulation for houses. barded by the sun's high-energy radiation. E3 CFCs
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^^^Pp.,^^^jfef^S18^here. But two chemists, F. __ .atoms into the stratosphere, adding much more
Ire began con- than the amount of chlorin<; supplied naturally by I
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rine buildup from CFCs would spell severe trouble
extremely stable in the lower atmo-
i=£Sphere, ffiey could drift up for the ozone layer. According to their predictions,
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stratospheric ozone.
in ozone
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-------
SSTs or CFCs, would allow more ultraviolet light to
reach the Earth's surface—an effect that holds se-
vere consequences for life on the planet. Expo-
sure to ultraviolet light enhances an individual's
risk for skin cancer and cataracts, so an increase in
this radiation could lead to more cases of such
diseases. Ultraviolet light also harms food crops
and other plants, as wejl,as many species ofanimals.
Thus the world faced two ozonei-related^envi-
ronmental issues in the first half ofjhe3p70s. In
'- uJ
terms of .SSTs, policy makers had" to jiecide'
•whether, to build such plaaek With Cfts?j the
question was whether,to limit the, production and
\,
use of these^chemicals. TO
Of all the countries considering SSTs, the United
States had planned the largest fleet, and it addressed •
this issue rather quickly. When preliminary scien-
tific studies suggested the planes would signifi-
cantly ,thoxthe_ozone Jiayer^jthe U.S. government
J, decided against the proposed fleet.
Political leaders, faced a much, tougher decision
"on the subject,pf,.CFCs. For example, in the United
States, Jhese^extremely reliable chemicals formed
•^ -W -Wr M-^*"*^ •• £ *S
/ thecentejfofamulti-billion-doIlarJnHustry. Though
tfieJlo'^land/Molina'hypothesis warned that CFCs
might endanger the health of the planet's inhabit-
ants, officials feared that a ban on such chemicals
would disrupt many segments of society. Was it
worthwhile to face economic hardships solely
: Tfie,chlorine chemistry ttiat causes ths ttestfuctlon. of ozone molecules is initiated by
solar radiation, which breaks up a chiorof luococatfionmalBcute to yield a chlorine atom.
This highly chemically reactive atom captures.one of the oxygen atoms from an ozone
.molecule,forming a.new chlorine-oxyge.n molecule.Jut this molecule will eventually
react with an oxygen atom which frees the chlorine atorriagam When tt finds another
-------
For millennia, ozone abundances varied Hutu /
' , - ? . • ^ //1
because of a scientific hypothesis and its pre-
dicted effects?
Decision makers also knew that the ozone layer
belonged to the entire world, meaning that all
countries would have to address the problem.
Stratospheric Ozone: The First Decade
(1974-1984)
Would CFCs really bring significant harm to the
ozone layer? That was the question politicians were
asking in 1974, and the scientific community set out
to provide an answer.
CteaninfP—-Sther
s.^: ,i * \ wa^-^ji
The human-made chlorofluorocarbons (CFCs) were "miracle" compounds. Their uses
proved to be manyfold. They cooled refrigerators, propelled spray from cans, filled the
insulating bubbles In foam, and cleaned delicate electronic parts. The rapid worldwide
growth in the use of these ozone-depleting compounds in the mid-1980s rekindled
international debate over whether their production should be curtailed.
Atmospheric researchers had to judge the seri-.
ousness of the problem. -If ozone levels were to
decline by only 1 percent in the next.50 years,
nations would have4ittie cause for concern.- On the
other hand, a substantial drop in ozone levels could
jeopardize the world. -
The first attempts to' assess the problem pro-
duced dire forecasts, suggesting that CFCs could
destroy perhaps half the ozone shield by the.
middle of the next century. Yet experts did not
, know how much to believe these early estimates,
because they were based on, a very simplistic under-
standing of chemical reactions in the stratosphere. .
It was like trying to decipher a partially com-
pleted jigsaw puzzle, spread out on a table.
Scientists wondered what the missing pieces
looked like and whether they would change the
emerging picture.
Over the next few years, researchers took many
different routes toward filling in the gaps in the
ozone puzzle. ^ Experiments in the laboratory
allowed chemists to gauge how quickly chlorine
destroyed ozone molecules. Other scientists
launched balloons tharcarried instruments up into
the stratosphere, where they measured the,con-
centrations of key chemicals that controlled ozone
levels. All this information fed into new computer
models that predicted how chemicals would affect
the ozone layer. ,
By 1976, many experts had grown convinced
that CFCs did indeed presents serious threat. In the
United States—the world's largest producer.and.
Reports to the Nation • Fall 1992
-------
>ut recently
'.O;
user of CFCs—the public called for the government so identifying the subtle signs of unnatural ozone
to place limitations on these chemicals. Civic
leaders launched boycotts against items that used
CFCs, and some companies even eliminated the
compounds from their products.
The U.S, and some other governments respond-
ed in 1979 by banning the sale of aerosol cans
containing CFCs. Because spray cans represented
the largest use of these chemicals, the ban led to an
abrupt leveling off of CFC production. [2|
After the spray can decision, the ozone issue
quickly receded from worldwide headlines. But
atmospheric researchers knew that danger still
threatened the protective ozone layer. While CFCs
no longer filled U.S. aerosol cans, companies
continued to produce these chemicals for use in air
conditioners, in insulation, and in the cleaning of
electronic parts. What's more, most countries
aside from the United States con-
oxygen Molecule
tinued to use CFCs in spray 0zoneMolecule
cans. So even as the threat to
the ozone layer slipped from
the public spotlight, scientists
extended their investigations
"into, the problem.
Researchers also began
watching the ozone layer more
closely, searching for evidence
that chlorine pollution had already started
weakening the protective shield. They knew it
might be difficult to spot such destruction at first.
Ozone levels fluctuate naturally by several percent,
loss would be like to trying to hear someone
whisper a message across a crowded room.
The U.S. ban on CFC propellants in spray cans
caused a temporary pause in the growing de-
mand for the offending compounds. But world-
wide use of the chemicals continued, and.
levels of CFC production began to rise
again. By 1985, the production rate was
growing 3 percent a year.
The increase in CFC use rekindled
worldwide attention to the threat of
ozone destruction, spurring
countries in 1985 to sign an
international agreement
called the Vienna
Convention.
Free Chlorine Atom
An intact ozone shield (1) prevents much
of the ultraviolet radiation.from reaching the Earth's
•surface. A,thinning of the ozone shield (2) allows more solar
ultraviolet rays .to reach the surface of the Earth. Such radiation is Known to
increase the number of skin cancers and cataracts in humans. It is also harmful to both
terrestrial and ad.uat.ic ecosystems. Scientists in the 1970s were predicting that the
impacts of such harmful .ultravipletTadiation could/become very significant .indeed If
humans continued to produce more and more GFCs.
CFC
Molecule
,(Vepprts .*<*' the Ma.tion -* Fs(M992
-------
The convention called on negotiators to draw .up. a.
plan for worldwide action-on this issue. It also
required scientists to summarize the latest
information on the atmospheric consequences of
CFCs and related bromine-containing chemicals
called Halons, which had grown popular over
die previous decade because of their ability to
extinguish fires. Collectively, CFCs and Halons fit
under the name halocarbons.
Using the most complete models, experts
predicted that if levels of halocarbon production
continued to increase as they had in the past,
ozone concentrations in the stratosphere would
drop by about 5 percent by the year 2050.
Although much less severe than the predictions
of earlier years, even a 5 percent decrease would
still allow a very serious surge in the amount,of
ultraviolet radiation reaching the Earth's surface,
causing millions of new cases of skin cancer in
the United States alone. FJT]
By the time of the Vienna Convention, scientists
remained uncertain whether ozone levels had
actually started to drop. The research community,
nonetheless, warned that countries could not af-
ford to take a wait-and-see approach. Halocar-
bons present an insidious danger for the future
because they can survive in the atmosphere for
decades; some can last several centuries. That
means even if the entire world stopped producing
such compounds instantly, the halocarbons al-
ready in the atmosphere would continue to dam-
age the ozone layer for more than 100 years.
Many governments thought it critically-important
to limit the chemicals as soon as possible, • .
Then in May of 1985, shocking news spread
throughout the scientific community. British re-
searchers reported finding dramatic -declines in:
ozone values over Antarctica each, spring—actual
"holes" in the ozone layer. Atmospheric scientists
didn't know how to explain, these large and unan-
ticipated changes. Some proposed that natural .
processes were at work, while others thought itwas
the first sign that halocarbons were wearing, away
the protective ozone shield., -,
Despite uncertainty about the Antarctic.
phenomenon's cause, scientists firmly believed,
halocarbons 'would eventually deplete the :global_
ozone .shield Their certainty arid.the jarring
unexpectedness of.the. ozone hole's appearance
motivated countries to act; In September 1987,
diplomats from around the world met in Montreal
and forged a treaty unprecedented in the history of
international .negotiations. Environmental minis-
ters from 24 nations, representing most ^of the.
industrialized world, agreed to set sharp limits on
the use of CFCs andHalons, According:to thetreaty,
by mid-1989 countries wo;uld freeze their produc-
tion and. use .of halocarbons at 1986 levels.. Then
over the next-ten years, they would .cut- CJFC
production and use in half. [g|
For scientists and policy makers,, the Montreal
Protocol marked a truly profound moment.
When negotiators drew up the treaty, they were
motivated by concerns about Juture ozone loss,
Reports to the Nation 'Fall 1992
-------
rather than by direct observations of current ozone
destruction by CFCs. (Certainly the ozone hole in
Antarctica had unnerved world leaders, but it was
by no means clear whether chemical pollutants
had caused this decline.) Thus, the agreement
was based primarily on confidence in a theory.
The Montreal Protocol established a new way of
viewing environmental problems. In the past, the
world had addressed such issues only after damage
grew noticeable. For example, nations agreed to
limit above-ground nuclear
tests once it became evident
these explosions poisoned the
air and water with radioactiv-
ity. The Montreal agreement,
however, tackled the ozone
issue early, demonstrating a
heightened sense of environ-
mental responsibility.
The framers of the protocol
also broke new ground in an-
other way: they realized their
agreement might not suffice if
future scientific work revealed
that the ozone layer faced even
greater danger. Uppermost in
their minds was; concern over
the Antarctic ozone hole and its
possible implications for global
ozone. The diplomats therefore
included a provision calling for
negotiators to reconvene in 1990
After it was hyppthesized.that CFCs could destroy ozone, researchers
focused on quantifying-this theory. Some hpisted'instrurnents into the.
stratosphere with huge balloons. ..Others probed.tlie inrterworkings.of
the ozone-destroying chemical reactions in the laboratory Still others
crafted all.'of this information into .computer models, which'foretold
mounting ozone losses if CFC usage continued to grow.
to examine any new scientific or technical information
that might necessitate adopting deeper cuts.
The Ozone Years: 1985-1989
The ozone hole was born in the-late 1970s, long
before the Montreal Protocol was signed. Like a
leak in the roof over the distant part of a house, the
hole at first grew unnoticed by any human being
living below. {§]
Each spring, ozone abundances over the ice-
covered continent dropped be-
low normal and then rose
gradually toward normal
amounts in summer. And each
year, the springtime losses
grew worse.
A British team, which had
measured ozone levels over
the Antarctic coast since 1956,
first began. noticing the phe-
nomenon in the early 1980s.
But it was hard to swallow the
evidence at first. Was the
ozone hole real, or were the
instruments malfunctioning?
wondered the scientists. Af-
ter checking and rechecking
the instruments, the British re-
searchers grew confident of
their discovery. In 1985, they
announced their startling
news to the rest of the world.
Reports to the Mali on -'Fa/11992
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.1979
Atmospheric experts moved quickly to deter-
mine whether the ozone hole was real. Consulting
measurements made by satellite-borne and balloon-
borne instruments, they found evidence confirm-
ing the springtime ozone depletion. Even more
staggering, measurements showed the hole
extending over die entire Antarctic continent.
The discovery of the ozone depletion
blindsided the scientific community, catch-
ing it totally off guard and without a
suitable explanation. But within a few
months, theoretical scientists came up,
with three competing ideas that could
explain why the ozone hole had devel-
oped over Antarctica.
One group of scientists focused on
the solar cycle—the periodic waxing
and waning, of the sun's energy output.
Noting that solar radiation had grown
particularly strong in the early 1980s,
some researchers proposed the intense
radiation had created above-normal levels
of reactive nitrogen chemicals in the strato-
sphere, [g] These compounds could then con-
centrate over Antarctica and destroy ozone there.
A second group suggested that natural changes
in stratospheric winds were responsible. Accord-
ing to this "dynamical" theory, the ozone hole
resulted from changes in the system of air motions
that transport ozone and establish its amount in
the polar regions. [QJ
Bellingshausen'
Reports to the Nation • Fall 1992
-------
1991
.Antarctica—the "last place on Earth." But.here occurred the first large-scale ozone
losses British scientists discovered that in the mid-1970s, the ozone layer over
.Antarctica began to thin.-du'ring'each springtime.By the mid-;! 980s,. the magnitude of
,these_seasonal losses had grown to 50 percent; which was'rnuch greater than any
•known natural variation. The Antarctic ozone "hole" had been "discovered, presenting
both scientists and policy makers vi/ith.a complex puzzle.
Both the solar cycle and dynamical theories
stressed natural processes as a cause for the deple-
tion But a third theory held that human-made
chemicals deserved blame According to this idea,
the cold conditions above Antarctica amplified the
* ozone-destroying power of CFCs and Halons,
accelerating the loss in this region [g
- The three separate theories held profoundly
different implications for the world If halo-
'{ ^
carbon pollution created the hole, then
scientists had gravely underestimated the
chemicals' destructive power, and the
ozone layer faced even more danger than
previously-thought But if the hole formed
because of natural processes, then humans
could breathe a sigh of rekef
With very little known about the Ant-
arctic ozone losses, atmospheric research-
ers could not tell which theory was correct.
Yet they recognized that political leaders
would need an answer as soon as possible.
1 The signers of the Montreal Protocol would be
meeting to review the limitations on halocar-
bons, and it was critical to know whether these
chemicals lurked behind the ozone hole [J]
The scientific community threw itself at the
problem, launching several field expeditions aimed
at solving the nddle of the ozone depletion In
September of 1986, a hastily assembled team
hurned off to McMurdo Station in the Antarctic
Using ground-based instruments and balloons to
probe the stratosphere, this team found high levels
Reports to Vh-e "Na.t.i on "- FaH.1992
-------
u
o
P
0)
o
REACTIVE NfTROGEN
Sunspots?\
of ozone-destroying compounds. A year later, the
United States, in conjunction with other countries^
sent a massive group of more than 100 scientists,
engineers, and technicians to Punta Arenas, Chile,
at the southern tip of South America. From this
distant base, two research airplanes flew into the
dangerously cold Antarctic sky to gather, conclusive
data about die mysterious affairs in the stratosphere
over that icy land. Other scientists returned to
McMurdo for further measurements.
By October 1987, the researchers came back
from die Soudiern Hemisphere with a dark mes-
sage for die world: blame for die ozone hole falls
On human shoulders.
The expeditions
showed that
chlorine and
Scientists probed the Antarctic stratosphere
with ground-based remote-sensing equipment
and with high-flying research aircraft launched
from nearby bases. Similarly, they addressed whether
such ozone losses could occur over the Arctic. 'Because
o( the ozone "hole," the distant poles are, ironically, the most
extensively chemically studied regions of our planet.
bromine pollution had. shifted die fragile chemical
balance in die Antarctic,, thereby draining .diose;
skies of ozone during the spring. ,
- Ozone loss is accelerated over die frozen conti-
nent because die. Antarctic stratosphere contains
cloud particles not normally present in warmer
climes. ^] These icy particles have a critical effect
on die chlorine and bromine pollution floating in
die stratosphere. Normally, the chlorine and bro-:
mine are largely locked into "safe" compounds mat
cannot harm ozone, but die ice particles transform
diem into destructive chemicals tiiat. can break
apart ozone molecules with amazing efficiency. In
1987, ozone concentrations above Antarctica fell to :
half their normal levels, and die hole spread across
an area die size of die United States.
Evidence gathered during diese expeditions and
new data .from laboratories back home
enabled scientists to fashion a,con-
sistent theory to explain die hole.
In the prelude to, ozone
depletion, ice particles form
during the polar night,
when"several months of
darkness descend on
Antarctica and tempera-
tures plummet below
-80°G (-112°F) in the strato-
sphere. On tiiose.floating
ice particles, reactions: convert
chlorine from die "safe" to die
Reports to the Nation 'Fall 1992
-------
Meteorology?
Chemistry?
"destructive" form. The real action begins when
the sun returns to this part of the world during
springtime, energizing the chemical cycle that
destroys ozone. Wind patterns during winter and
spring contribute by isolating the Antarctic strato-
sphere from warmer air to the north.
The ozone hole forms only in Antarctica because
this region has a unique combination of weather
conditions: it is the coldest and most isolated spot
on Earth. But somewhat similar conditions exist in
the Arctic, and scientists ^wondered whether the
North also suffered from ozone loss. Even small
depletions in this region would represent cause for
concern, because many people live in northern
latitudes potentially affected by Arctic ozone loss.
So in 1988, two small teams traveled to Greenland
and Canada to gather data. A year later, an
extensive group headed to Norway to take mea-
surements with the two airplanes that helped to-
solve the Antarctic puzzle. ^
The northern expeditions revealed that during
wintertime, the Arctic stratosphere has the same
types of destructive chlorine and bromine com-
pounds that cause the problems in the Antarctic.
Indeed, when scientists returned to the Arctic for an
extended study in 1991 and 1992, they discovered
strong hints that such compounds had destroyed
significant amounts of ozone in the polar region.
But because the Arctic atmosphere is not as isolated,
the ozone losses there appear to be much smaller than
those in Antarctica—at least for the present. IS
Between trips to the, ends of the Earth, atmo-
spheric scientists during this period also stepped
up their search for signs of a global erosion in the
ozone layer. An international panel of experts
came together to scrutinize measurements made
by satellites and by ground-based instruments
around the world. In 1988, they reached a verdict:
global ozone levels had declined over the past 17
years, mainly in the winter. Normal processes
such as the solar cycle had caused part of the drop,
but natural effects could riot explain the entire
ozone loss.
The news grew even worse. An international
panel announced that ozone levels had dropped
by measurable amounts not only in winter and
spring but also in summer. Because people
spend far more time outdoors during summer,
ozone loss at this time of the year poses the
greatest threat to the health of humans. QU
Scientists suspect that CFCs and Halons are to
blame for much of the ozone decline, which has
reached several percent over the midlatitudes of
the Northern Hemisphere—the segment of the^
globe^ that encompasses the United States and
Europe. But atmospheric researchers are not yet
fully confident that they know what mechanism
lies behind the drop. The largest changes have
occurred over the poles and neighboring
midlatitudes, leading some researchers to suggest
that loss near the poles has enhanced the decline
in global ozone levels. Others suspect that the
.R e p o r t s' t o t h e N at i o n .-' Fall 1992
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Spurred by the CFC - ozone hypothesis, scientists began closely watching the variations'
In global ozone, searching for the first sign of the predicted ozone losses. In the late
1980s, they began to see ozone losses, even outside of the polar regions, that could not
be explained by natural variation. These losses, which increase poleward from the
equator, appear to be related to the CFCs, but the details are not yet fully explained,
natural, thin layer of sulfur-containing particles in
the stratosphere could be involved in midlatitude
ozone loss, in a role somewhat similar,to that
played by ice particles over Antarctica.
The fast-paced research of-the late 1980s re-
vealed that tlie original Montreal Protocol would
not go far enough toward protecting the fragile
ozone layer. Even with the 50 percent cuts
mandated by the treaty, levels of chlorine and
bromine would still rise in the stratosphere, mean-
ing that ozone loss would only worsen with time.
In June 1990, diplomats met in London and
voted to significantly strengthen the Montreal Pro-.
tocol. The treaty calls for a complete phaseout of
CFCs by the year 2000, a phaseout of Halons
(except for essential .uses)- by-.2000, and a;
rapid phaseomt of other ozone-destroying
chlorine compounds, (carbon tetrachloride by,
2000 and methyl chiloroform by 2005).
The treaty also attempts to make the
phaseouts fair for developing countries,
which cannot easily afford the higher-priced
substitutes that will replace banned com-
pounds. The revised agreement establishes
an environmental fund-—paid for by developed
nations—to help developing nations switch over to
more "ozone-friendly" chemicals. :,
Our Ozone Layer: Present and Future
But many pieces of the ozone puzzle remain
missing, and scientists wonder whether new ozone
problems will, develop in the hear future. Experts
are exploring several unanswered questions, in-.;
eluding: ••.-'"..
-: - • What surprises lurk in the" next decade or so?
Even with the amended protocol, chlorine abun-
dances will continue to rise until around the turnpf
the century. ; . ., • '_
• Will ozone losses grow worse in the Arctic as
, chlorine abundances increase? : ;
• How safe are the CFC substitutes? Will some of
them significantly contribute to ozone loss, global
warming, or other environmental problems?
• How appropriate -is it to allow, countries to
continue "essential" uses of;'the.powerful ozone
Reports to the Nation ''Fall 1992
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For the first time in my life I saw the horizon as a curved line It was
accentuated by a thin seam of dark blue light—our atmosphere, Obviously
this was not the ocean of air I had been told it was so many times in my life
I was terrified by its fragile appearance
Ulf Merbold, German Astionaut
depleting Halons? The current treaties permit
these Uses.
• Are there other compounds that significantly
deplete the ozone layer and hence could
deserve attention under the Montreal Pro-
tocol—such as methyl bromide, which
is used widely as a fumigant? g|
• How will polar ozone de-
struction affect populated coun-
tries? Will the Antarctic hole"
cause ozone declines over Chile,
Argentina, and New Zealand? Will
Arctic losses spur drops in ozone concentration
over Canada, Scandinavia, the United States, and
the former Soviet Union?
• How much do the natural particles in the
stratosphere, other than the icy polar clouds, accel-
erate the chemical destruction of ozone at
midlatitudes?
• How will large volcanic eruptions—which
can inject immense amounts of dust into the
stratosphere—affect the ozone layer when the
chlorine from CFCs reaches unprecedented abun-
dances?
• How will the ozone hole and global ozone
losses affect worldwide weather and climate?
• Does a proposed new class of high-altitude
aircraft threaten the ozone layer?
Decision makers will need answers to such
questions as they continue to revisit their interna-
tional agreements in the future and ask if these are
adequate in light of new research findings.
The Montreal Protocol provides a dramatic ex-
ample of science in the service
of humankind. By quickly
piecing together the ozone
puzzle, atmospheric research-
ers revealed the true danger of
the
halocarbons, allowing world lead-
ers to take decisive action to protect
ozone layer.
This international agreement represents a
r „
critical step toward saving the world's ozone layer.
But perhaps more importantly, it has taught scien-
tists and policy makers an invaluable lesson about
addressing environmental problems. Negotiations
on this issue mark the first time the nations of the
world have joined forces to protect the Earth for
future generations.
The treaty can serve as a crucial apprentice-
ship for world leaders and scientists, who now
face an even more daunting environmental mat-
ter—the threat of global greenhouse warming
that looms over the future of this planet. The
successful ozone agreement offers hope that
scientific understanding can once again provide
the foundation for responsible' action by the
international community.
Re.p o rts t.o th e Nati,6 n:,« fall 1992
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Writers and Contributors
Daniel L Attrition, National Oceanic and , .
Atmospheric Administration
Richard Monastersky, Science News
with Input from:
John A. Eddy, Consortium for International Earth
Science Information Network
J. Michael Hall, National Oceanic and
Atmospheric Administration
Eileen Shea, National Oceanic and Atmospheric
Administration
Our Ozone Shield is the second in a series of
publications on climate and global change intended
for public education. They are a joint effort of the
UCAR Office for Interdisciplinary Earth Studies and
the NOAA Office of Global Programs, for the purpose
of raising the level of public awareness of issues
dealing with global environmental change. The
reports are written by knowledgeable scientists and
science writers on timely subjects and guided by a
scientific Editorial Board. The first in the series, The
Climate System, appeared in winter 1991.
Editorial Board
Daniel L Aibiitton, National Oceanic and Atmospheric
Administration
Francis Bretherton, University of Wisconsin
Robert Dickinson, University of Arizona
John A. Eddy, Consortium for International Earth Science
Information Network
J, Michael Hall, National Oceanic and Atmospheric
Administration
Stephen Schneider, National Center for Atmospheric
Research
Design, Illustration, and Production
Internetwork, Inc., Del Mar, CA. Payson R. Stevens,
Eric Alison, Leonard Slrota, Patrick Howell
For additional copies contact the UCAR Office for
Interdisciplinary Earth Studies, PO Box 3000, Boulder,
Colorado 80307-3000; phone (303) 497-1682;
fax (303) 497-1679
Image Credits
Atlcomputergraphicilfustrations: InterNetwork, Inc. Cover/
Page 1: NASA Space Shuttle, Pages 2-3: All images except
tower right © Payson R. Stevens; lower right NASA/
Goddard Space Flight Center, courtesy MarkSchoeberl and
Gene Carl Feldman. Page 9: top three images © Payson R.
Stevens. Page 13: National Centerfor Atmospheric Research/
NSF. Pages 14-15: National Oceanic and Atmospheric
Adminlstration/NRSC. Quote Page 19: The Home Planet,
Kevin W. Kelley and ASE, © 1988, Addison Wesley. Pages
20-inslde back cover: © Payson R. Stevens.
10/92:500K
Reports to the Nation 'Fall 1992
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