Download Global change problems

Ch 4. The three modern global change
problems.
1
Earth has been changing and will continue to
do so. It is changing faster today than it
ever has. The major reason is human
activity.
1. Ozone depletion; Ozone hole in South
2.
3.
Pole
deforestation;
Greenhouse gases and global warming
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Vertical Structure of the Atmosphere
4 distinct layers
determined by
the change of
temperature
with height
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Zonally averaged, annual mean total column ozone in
Dobson Units (DU; 1 DU = 2.69 × 1016 O3/cm2)
from ground-based measurements combining Brewer,
Dobson, and filter spectrometer data WOUDC (red),
OME/SCIAMACHY/GOME-2 GSG (green) and
merged satellite BUV/TOMS/SBUV/OMI MOD V8
(blue) for (a) Non-Polar Global (60°S to 60°N), (b)
NH (30°N to 60°N), (c) Tropics (25°S to 25°N),
(d) SH (30°S to 60°S) and (e) March NH Polar
(60°N to 90°N) and October SH Polar. (Adapted
from Weber et al., 2012; see also for abbreviations.)
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Global lower stratospheric departure of temperature from average
since 1979, as measured by satellites. The large spikes in 1982 and
1991 are due to the eruptions of El Chicon and Mt. Pinatubo,
respectively. These volcanos ejected huge quantities of sulphuric acid
dust into the stratosphere. This dust absorbed large quantities of solar
radiation, heating the stratosphere.
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• Ozone depletion describes two distinct, but
related observations:
(1) a slow, steady decline of about 4% per decade
in the total volume of ozone in Earth's
stratosphere (ozone layer) since the late 1970s,
(2) a much larger, but seasonal, decrease in
stratospheric ozone over Earth's polar regions
during the same period.
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Image of the largest Antarctic ozone hole ever
recorded (September 2006).
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Ozone over Antarctic during Oct.
8
It shows a sharp drop
beginning in the early
1970s. The graph to
the left shows longterm ozone levels
over Arosa,
Switzerland. Although
ozone levels rise and
fall in natural cycles,
the average level
remained constant
from 1926 until 1973.
Beginning in 1973,
however, and
continuing through
2001, ozone levels
have dropped at a
rate of 2.3 percent /
decade.
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Why does a ozone hole form over Antarctica?
•
Firstly, strong winds blowing around the continent form,
this is known as the "polar vortex" - this isolates the air
over Antarctica from the rest of the world.
Secondly, clouds form called Polar Stratospheric
Clouds. Clouds turn out to have the effect of
concentrating the pollutants that break down the ozone,
so speeding the process up.
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Why does a ozone hole form over Antarctica?
The ozone hole is
caused by the effect of
pollutants in the
atmosphere destroying
stratospheric ozone.
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Too much ultra-violet light can result in:
•
•
•
•
Skin cancer
Eye damage such as cataracts
Immune system damage
Reduction in phytoplankton in the oceans that
forms the basis of all marine food chains
including those in Antarctica.
• Damage to the DNA in various life-forms. So far
this has been as observed in Antarctic ice-fish
that lack pigments to shield them from the ultraviolet light (they've never needed them before)
• Probably other things too that we don't know
about at the moment.
14
Deforestation
Deforestation is the permanent removal of forest cover from an
area, and the conversion of this previously forested land to other
uses.
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Deforestation affects
Carbon balance
Hydrological cycle
Radiative energy balance
Biodiversity
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Statistics
It has been estimated that about half of the earth's mature tropical forests
— between 7.5 million and 8 million km2 of the original 15 million to 16
million km2 , have now been cleared since 1947.
 North America and Europe – already done
 85% of old growth forests in US destroyed by
settlers – most replanted
 Parts of Pacific NW and Alaska – deforesting now
as fast as Brazil
Canada:
One case of deforestation in Canada is happening in Ontario's boreal forests,
near Thunder Bay, where 28.9% of a 19,000 km² of forest area had been lost
in the last 5 years and is threatening woodland caribou. This is happening mostly
to supply pulp for the facial tissue industry. In Canada, less than 8% of the boreal
forest is protected from development and more than 50% has been allocated
to logging companies for cutting.
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 Tropics
 Rainforests 50 years ago covered 14% of the world's land
surface and have been reduced to 6%, and that all tropical
forests will be gone by the year 2090
 Brazil – slash and burn; Amazon – 200% increase in
deforested area from 1979 - 1988
Some scientists have predicted that unless significant measures
(such as seeking out and protecting old growth forests that have not
been disturbed) are taken on a worldwide basis, by 2030 there will
only be ten percent remaining.
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The reasons
 Disappearing at a rate of tens of thousands of square miles per year
 Land clearing in developing countries for farming
and ranching (e.g., Brazil)
 Wood as a fuel (e.g., 90% of Africans use wood as
primary fuel)
 Ballooning populations in developing countries
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The effects
 Lowered oxygen production levels
 Increased CO2
 Changed climate (radiation, temperature) and hydrologic cycle
 Landslides
 Loss of fauna associated with the forests
 Current extinction rate of 50,000 species per year
 Rate reflects fact that most fauna and flora in
tropics are disappearing
 Loss of soil value for farming (formation of laterites) ;
increased soil erosion (i.e., global erosion rate of 25.4 billion
tons of top soil per year)
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Dust Storm in Beijing, China on March 20, 2002. It lasted 52 hours.
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Effects
 Cycle (vicious circle):
 deforestation  soil erosion and loss of wood
materials  lowered productivity of soil and loss
of wood source  increased human needs 
enhanced deforestation
 e.g., 40-50 million trees removed in Haiti each year
– correlates with 7x increase in food aid over
last 20 years
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Global warming
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The balance of evidence suggests that there is
a discernible human influence on global
climate
Intergovernmental Panel on Climate Change (United Nations), Second Assessment
Report, 1996
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There is new and stronger evidence that most of
the warming observed over the last 50 years is
attributable to human activity'
Intergovernmental Panel on Climate Change (United Nations), Third Assessment Report,
2001
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`Most of the observed increase in globally
averaged temperatures since the mid-20th
century is very likely due to the observed increase
in anthropogenic greenhouse gas concentrations’
Intergovernmental Panel on Climate Change (United Nations), Fourth
Assessment Report, 2007
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Human influence has been detected in warming of the
atmosphere and the ocean, in changes in the global
water cycle, in reductions in snow and ice, in global
mean sea level rise, and in changes in some climate
extremes. This evidence for human influence has grown
since AR4. It is extremely likely that human influence
has been the dominant cause of the observed warming
since the mid-20th century.
Intergovernmental Panel on Climate Change (United Nations), Fifth
Assessment Report, 2013
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Discovery of the Greenhouse Effect
Joseph Fourier (1827)
Recognized that gases in the atmosphere might trap the
heat received from the Sun.
John Tyndall (1859)
Careful laboratory experiments demonstrated that several
gases could trap infrared radiation. The most important was
simple water vapor. Also effective was carbon dioxide,
although in the atmosphere the gas is only a few parts in ten
thousand.
Svante Arrhenius (1896)
Performed numerical calculations that suggested that
doubling the amount of carbon dioxide in the atmosphere
could raise global mean surface temperatures by 5-6°C.
Guy Callender (1939)
Argued that rising levels of carbon dioxide were responsible for measurable
increases in Earth surface temperatures. Estimated that doubling the
amount of CO2 in the atmosphere could raise global mean surface
temperatures by 2°C.
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GREENHOUSE EFFECT?
Glass allows visible radiation to pass
through the glass which absorbs thermal
radiation and re-emits some of it back into
the greenhouse --- like a radiation blanket.
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Radiation is emitted out to space by these gases from level
somewhere near the top of the atmos. – typically from between 5 and
10km high. Here, temperature is much colder -30 – 50C or so colder
than at the surface. => emitting less radiation to space. So: absorb
radiation emitted from the earth surface but then to emit much less
radiation out to space.
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The enhanced greenhouse effect
F = T4
 = 5.67 x 10-8 W/m2/K4
average levels from which thermal radiation leaving
the atmosphere originates
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Component of the radiation (in watts per square meter)
which on average enter and leave the earth’s atmos. and
make up the radiation budget for the atmosphere.
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Planetary energy balance
• Earth is at steady state:
Energy emitted by Earth =
Energy absorbed
• E emitted = (area of Earth)   Te4
= 4 Re2   Te4
..(1)
(Te= Earth’s effective rad. temp., Re= Earth’s radius)
• E absorbed = E intercepted - E reflected
• Solar E intercepted = S Re2 (solar flux S)
• Solar E reflected = AS Re2 (albedo A)
• E absorbed = (1-A) S Re2
• (1) => 4 Re2   Te4 = (1-A) S Re2
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Magnitude of greenhouse effect
•  Te4 = (1-A) S/4
• Te = [(1-A) S/(4  )]1/4 (i.e. fourth root)
• Te = 255K = -18°C, very cold!
• Observ. mean surf. temp. Ts = 288K = 15°C
• Earth’s atm. acts as greenhouse, trapping
outgoing rad.
• Ts - Te = Tg, the greenhouse effect
• Tg = 33°C
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Greenhouse effect of a 1-layer atm.
•Energy balance at Earth’s surface:
Ts4 = (1-A)S/4 + Te4
..(1)
•Energy balance for atm.:
Ts4 = 2 Te4
.. (2)
S/4
Te
AS/4
Te4
Atm.
(1-A)S/4
Ts
Ts4
Te4
Earth
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Subst. (2) into (1):
Te4 = (1-A)S/4 ..(3) (same eq. as in last lec.)
Divide (2) by ; take 4th root:
Ts = 21/4 Te = 1.19 Te
For Te = 255K, Ts = 303K. (Observ. Ts = 288K)
Tg = Ts - Te = 48K,
15K higher than actual value.
• Overestimation: atm. is not perfectly
absorbing all IR rad. from Earth’s surface.
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• Weather forecasting also uses atm. GCMs.
Assimilate observ. data into model. Advance
model into future => forecasts.
• Simpler: 1-D (vertical direction) radiativeconvective model (RCM):
Doubling atm. CO2 => +1.2°C in ave.sfc.T
• Need to incorporate climate feedbacks:
• water vapour feedback
• snow & ice albedo feedback
• IR flux/Temp. feedback
• cloud feedback
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Water vapour feedback
• If Ts incr., more evap. => more water vapour
=> more greenhouse gas => Ts incr.
• If Ts decr., water vap. condenses out =>
less greenhouse gas => Ts decr.
• Feedback factor f = 2.
• From RCM: T0 = 1.2°C (without feedback)
=> Teq = f T0 = 2.4°C.
Ts
(+)
Atm. H2O
Greenhouse effect
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Snow & ice albedo feedback
• If Ts incr. => less snow & ice => decr.
planetary albedo => Ts incr.
snow &
ice cover
Ts
(+)
planetary albedo
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IR flux/Temp. feedback
• So far only +ve feedbacks => unstable.
• Neg. feedback: If Ts incr. => more IR rad.
from Earth’s sfc. => decr. Ts
Ts
(-)
Outgoing IR flux
•But this feedback loop can be overwhelmed
if Ts is high & lots of water vap. around
=> water vap. blocks outgoing IR
=> runaway greenhouse (e.g. Venus)
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Climatic effects of clouds
• Without clouds, Earths’ albedo drops from
0.3 to 0.1.
By reflecting solar rad., clouds cool Earth.
• But clouds absorb IR radiation from
Earth’s surface (greenhouse effect) =>
warms Earth.
• Cirrus clouds: ice crystals let solar rad.
thru, but absorbs IR rad. from Earth’s sfc.
=> warm Earth
• Low level clouds (e.g. stratus): reflects
solar rad. & absorbs IR => net cooling of
Earth
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• IR rad. from clouds at
T4
• High clouds has much
lower T than low clouds
=> high clouds radiate
much less to space than
low clouds.
=> high clouds much
stronger greenhouse
effect.
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Uncertainties in cloud feedback
• Incr. Ts => more evap. => more clouds
• But clouds occur when air is ascending, not
when air is descending. If area of
ascending/descending air stays const.
=> area of cloud cover const.
• High clouds or low clouds? High clouds
warm while low clouds cool the Earth.
• GCM’s resolution too coarse to resolve
clouds => need to “parameterize” (ie.
approx.) clouds.
• GCM => incr. Ts => more cirrus clouds =>
warming => positive feedback.
=> Teq = 2 -5°C for CO2 doubling
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Greenhouse Gases
Water Vapor:
Carbon Dioxide (CO2)
CH4 methane,
N2O = nitrous
oxide...
NATURAL GREENHOUSE EFFECT
Evaporation = > water vapor
Common name: marsh gas that can be seen
bubbling up from marsh area where
organic material is decomposing.
plant and animal
respiration, the decay
of organic materials.
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ENHANCED GREENHOUSE EFFECT
The increase in carbon dioxide (CO2) has contributed
about 72% of the enhanced greenhouse effect to date,
methane (CH4) about 21% and nitrous oxide (N2O)
about 7%.
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• Water Vapor:
source: evaporation from Earth’s surface
location: the lowest 5 km of the atmosphere
residence time: 10 days
variation range: 0.1% - 4%
roles in atmosphere: source of moisture for
cloud; absorber of energy emitted by
Earth’s surface: greenhouse gas.
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Water Vapor
• Naturally
occurring
greenhouse
gas,
generally
unaffected
by humans.
Importance:
The Clausius-Clapeyron relationship (shown below) suggests that warmer air can
hold more water vapor. As the planet warms due to the greenhouse effect, more
water vapor will change global climate conditions.
By solving for water vapor (e), we can see that temperature (T)
increases the amount of water vapor.
Increased stratospheric
H2O vapour causes the
troposphere to warm and
the stratosphere to cool
and also causes increased
rates of stratospheric O3
loss.
Water vapour anomalies in the lower stratosphere (~16 to
19 km) from satellite sensors and in situ measurements
normalized to 2000–2011. (a) Monthly mean water vapour
anomalies at 83 hPa for 60°S to 60°N (blue) determined
from HALOE and MLS satellite sensors. (b) Approximately
monthly balloon-borne measurements of stratospheric
water vapour from Boulder, Colorado at 40°N (green dots;
green curve is 15-point running mean) averaged over 16 to
18 km and monthly means as in (a), but averaged over
30°N to 50°N (black)
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• Carbon Dioxide (CO2)
source: plant and animal respiration, the decay
of organic materials, and natural and
anthropogenic (human-produced).
Current concentration: 380ppm (parts per
million, i.e., 0.038%); a global increase in recent
decades.
The increase in carbon dioxide (CO2) has
contributed about 72% of the enhanced
greenhouse effect to date, methane (CH4) about
21% and nitrous oxide (N2O) about 7%.
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• Carbon is exchanged between the biosphere,
lithosphere, hydrosphere, and atmosphere of the Earth.
• Four reservoirs of CO2: atmosphere, ocean, biosphere
and sediments.
• Carbon cycle modeling. Models of the carbon cycle
can be incorporated into global climate models, so that
the interactive response of the oceans and biosphere on
future CO2 levels can be modeled. Such models
typically show that there is a positive feedback
between temperature and CO2.
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The “Carbon Cycle”
There is a natural
process by which
carbon dioxide is cycled
through the Earth's
ecosystems and
atmosphere.

The blue arrows
represent the natural
processes by which
living organisms emit
and absorb carbon
throughout their life and
death (e.g. Respiration,
photosynthesis,
decomposition)

The red arrows represent the “anthropogenic
flux” which is a scientific term for the human
effect on the carbon cycle, including
industrialization and fossil fuel burning.
"GtC" stands for GigaTons of Carbon
•
The land and ocean are large reservoirs to stock carbon
than atmos. For example, the release of just 2% of the
carbon stored in the oceans would double the amount
of atmos. CO2.
• At the time scales which we concern, CO2 is not
destroyed but redistributed among the various carbon
reservoirs. E.g., about 50% of an increase in atmos.
CO2 will be removed within 30 years, a further 30%
within a few centuries, and the remaining 20% may
remain in the atmos. for many thousands of years.
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The Human Footprint
•
5% of the world's population resides in the United States, creating ¼ of the total
greenhouse gas emissions.
•
For most people, their car is the main source of emissions. 22Lbs of CO2 is
produced from every gallon of gas. Do the math:
•
Number of miles traveled by car each year _10000_ , divide by average miles per gallon =
15__ gallons of gas, multiplied by 22 lbs CO2/gallon of gas = _14667_ pounds of CO2
•
The 1997 Kyoto protocol called for all people to limit their carbon emissions to 5.4
tons, or about 11,000 lbs, per year.
•
Some scientists believe that in order to reverse the damage caused by greenhouse
gas emissions, we would need to reduce our individual emissions down to 5,000 lbs
per year.
Solving the Carbon Dilemma:
What are some things that you can do to reduce your
carbon emissions?
Energy-efficient, energy-conserving electronics, lightbulbs, hardware
and other devices are available for almost anything. You can expect
that energy-efficient products are meant to last longer and will save
you money.

Reduce your dependency on cars!

Greenhouse gases
• Greenhouse gases (CH4 = methane, N2O =
nitrous oxide):
trap outgoing radiation from Earth’s surface
• Coal burning  Sulfur dioxide (SO2)  acid
rain.
• SO2  Sulfate aerosol, reflects sunlight =>
cooling.
• 1940-1970 cooling may be due to coal
burning.
• Coal burning incr. CO2 (long-term warming)
and incr. sulfate aerosol (short-term
cooling) [aerosol washed out by precip.]
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CO22 (ppm)
(ppm)
CO
1000
1000
O (ppb)
(ppb)
NN22O
2000
2000
CH44 (ppb)
(ppb)
CH
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From IPCC Report
Atmospheric CO2 concentrations-past 1000 years.
From “The earth system”
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Anthropogenic greenhouse warming
Atm. CO2:
• Keeling started measuring atm.CO2 in 1958 on Mauna
Loa, Hawaii
• Seasonal cycle (forests absorb CO2 in summer &
release CO2 in winter) + rising trend
From “The earth system”
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From “Global Warming”
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* The most important of the aerosols from anthropogenic forcing
are sulphate particles.
* Cooling effect;
* Life time: 5 days. So their effect is mainly confined to regions
near the sources of the particles.
From “Global Warming”
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Red: removing sulphate aerosols in 2000;
Blue: maintaining sulphate aerosols at the 2000 level.
From “Global Warming”
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• Some facts of global changes:
(1) Global warming:
Global mean surface temperatures have increased 0.5-1.0 F
since the late 19th century; The 20th century's 10 warmest
years all occurred in the last 15 years of the century. Of these,
1998 was the warmest year on record. The snow cover in the
Northern Hemisphere and floating ice in the Arctic Ocean
have decreased, sea level has risen 4-8 inches over the past
century.
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•
Multiple independent indicators of a changing global climate. Each line represents
an independently derived estimate of change in the climate element. In each panel
all data sets have been normalized to a common period of record. A full detailing of
which source data sets go into which panel is given in the Supplementary Material
2.SM.5.
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•
Independent analyses of many components of the climate system that would be expected
to change in a warming world exhibit trends consistent with warming (arrow direction
denotes the sign of the change), since 1970s.
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Figure SPM.2
LOSU: assessed level of scientific
understanding
From IPCC report
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The three serious problems
The three modern global change problems
discussed in this chapter-- global
warming, ozone depletion, or loss of
biodiversity
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The ozone depletion is the serious
problem because:
• It causes the most immediate damage to our
planet and its inhabitants
• It can cause skin cancer
• It occurs faster than global warming,
because global temperatures only rise 1
degree in 100 years so this is an
insignificant amount compared to the
decline in the total amount of ozone
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• Low-level ozone damages plants, reducing their capacity to take
up carbon dioxide and accelerating global warming. The study
suggests that projected increases of ozone concentration from
industrial sources will markedly reduce plant productivity. This
indirect effect could contribute significantly to global warming.
(Nature, 16, August 2007, by S. Sitch, P. M. Cox, W. J. Collins & C.
Huntingford)
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The loss of biodiversity is the serious
problem because:
• There is potential for recovery for the other problems: the
ozone layer could recover within a few generations and
greenhouse gas concentrations should return to “normal”
within a few million years.
• The recovery rate for species following extinction is tens
of millions of years.
• Once a species is gone, it is gone for good.
• It could cause an imbalance in the Earth’s ecosystem and
economy.
• Deforestation also contributes to global warming.
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Global warming is the serious problem
because:
• It affects the greatest number of people
• Migration of marine animals could result
• Rising sea level could result
• Cold climate species might die
• Ozone depletion and deforestation are both
confined to particular areas whereas global
warming is truly global
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