Transcript Intro-1 EOSC 112 Course Overview [text KKC, pp.]

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
2
• Ozone
source: O and O2 makes it through chemical process.
Location: in middle-layer atmosphere (stratosphere).
roles: absorb ultraviolet radiation from Sun.
3
Vertical Structure of the Atmosphere
4 distinct layers
determined by
the change of
temperature
with height
4
• 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.
5
• Ozone ( O
) is a form of oxygen, and protects the
earth’s surface from Sun’s harmful ultraviolet
radiation. Ozone depletion is the result of a
complex set of circumstances and chemistry .
3
•
•
Antarctic Ozone Levels in Fall
2003
The ozone hole is represented by
the purple, red, burgundy, and
gray areas that appeared over
Antarctica in the fall of 2003. The
ozone hole is defined as the area
having less than 220 Dobson units
(DU) of ozone in the overhead
column (i.e., between the ground
and space).
6
Image of the largest Antarctic ozone hole ever
recorded (September 2006).
7
Ozone over Antarctic during Oct.
8
• Mean total ozone over Antarctica during the month
of October
9
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.
10
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.
11
12
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
13
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
14
Why does a ozone hole form over Antarctica?
The ozone hole is caused by the effect of pollutants in the
atmosphere destroying stratospheric ozone. During the
Antarctic winter something special happens to the
Antarctic weather.
•
•
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.
15
Deforestation
16
Deforestation affects
Carbon balance
Hydrological cycle
Radiative energy balance
Biodiversity
17
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.
18
Tropical Rainforest
Earth's most complex biome in terms of both structure and species
diversity; abundant precipitation and year round warmth.
Climate: Mean monthly temperatures are above 64°F; precipitation is
often in excess of 100 inches a year.
Vegetation: 100 to 120 feet tall canopy.
Soil: infertile, deeply weathered and severely leached. Red color because
of high iron and aluminum oxides.
Fauna: Animal life is highly diverse
Distribution of biome: 10°N and 10°S latitude. Neotropical (Amazonia
into Central America), African (Zaire Basin with an outlier in West Africa;
also eastern Madagascar), Indo-Malaysian (west coast of India, southeast
Asia)
19
 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.
20
The problem
 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
 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)
21
Effects
 Lowered oxygen production levels
 Increased CO2
 Changed climate (radiation, temperature) and hydrologic cycle
 Loss of flora and fauna
 Increased soil erosion (i.e., global erosion rate of 25.4 billion
tons of top soil per year)
 Increased effects of floods, especially coastal (e.g., 10x increase
in catastrophic floods in Bangladesh)
 Landslides
 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
22
Global warming
23
24
25
`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
26
`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
27
`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 28
Discovery of the Greenhouse Effect
Joseph Fourier (1827)
Recognized that gases in the atmosphere might trap the
heat received from the Sun.
James 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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30
31
32
33
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.
34
Heat Transfer --- Convection
• Less dense warm air moves upward and
more dense cold air moves downward.
Convection is the dominant process for
transferring heat in the troposphere.
35
The distribution of temperature in a convective atmos.(red line). The green line
shows how the temperature increases when the amount of CO2 present in atmos. is
increased (in the diagram the difference between the lines is exaggerated). Also
shown for the two cases are the average levels from which thermal radiation leaving
the atmosphere originates (about 6km for the unperturbed atmosphere).
36
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.
37
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.
38
The enhanced greenhouse effect
F = T4
 = 5.67 x 10-8 W/m2/K4
average levels from which thermal radiation leaving
the atmosphere originates
39
Blackbody rad. curves for Sun & Earth
max = const./T
Temp. T in K
const. = 2898 m
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44
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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
46
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
47
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
48
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.
49
• 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
50
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
51
Snow & ice albedo feedback
• If Ts incr. => less snow & ice => decr.
planetary albedo => Ts incr.
snow &
ice cover
Ts
(+)
planetary albedo
52
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)
53
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.
55
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
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ENHANCED GREENHOUSE EFFECT
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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.
60
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.
• 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., 0.04%); 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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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.
• carbon is exchanged between the biosphere, geosphere, 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.
64
•
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 __ , divide by average miles per gallon =
__ gallons of gas, multiplied by 22 lbs CO2/gallon of gas = __ 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?
It's the act of consuming
difference.

less that will ultimately make a
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.]
68
Seasonal cycle of atmospheric CO2
(Mauna Loa record)
Atmospheric CO2 concentrations--recent.
69
Short-term variability
70
• 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.
71
Atmospheric CO2 concentrations--past
1000 years.
72
Short term climate change
Short
term
climat
e
Earth’s
chang
surface
temp.
e:
0.8
-0.8
1860
0.8
incr.
by 0.7
°C/cent -0.8
ury
10
2000
2000
00
73
Holland in 1565 (Little Ice Age)
(Pieter Bruegel)
74
•Cooling in 1940s-1960s => fear of
coming ice age!
•Volcanic eruptions => drop in temp. for
3 years (e.g., Agung 1963)
•Viking colony on Greenland lost by
early 1400s.
•Little Ice Age in late 1500s.
75
76
El Chicon Mexico,
1982
Mount Pinatubo, Philippines,
1991
Emitted millions of tons of sulfur dioxide
and ash particles.
Agung, Indonesia, 1963
77
London smog
in 1952
78
79
Red cross:
simulated global
mean Tem. (62
simulations);
black line: mean
of all
simulations;
blue round:
observed global
mean Tem.
80
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
81
82
CO2 (ppm)
CO2 (ppm)
CO2 (ppm)
1000
1000
1000
N2O (ppb)
N2O (ppb)
N2O (ppb)
2000
2000
2000
CH4 (ppb)
CH4 (ppb)
CH4 (ppb)
83
84
85
86
87
An increasing body of observations gives a
collective picture of a warming world and
other changes in the climate system
• Global mean surface temperature increase
(NH, SH, land, ocean)
• Melting of glaciers, sea ice retreat and thinning
• Rise of sea levels
• Decrease in snow cover
• Decrease in duration of lake and river ice
• Increased water vapor, precipitation and
intensity of precipitation over the NH
• Less extreme low temperatures, more
extreme high temperatures
88
Recent Range Shifts due to Warming
Species Affected
Location
Observed Changes
Alaska
Expansion into shrub-free areas
39 butterfly spp.
NA, Europe
Northward shift up to 200 km in 27 yrs.
Lowland birds
Costa Rica
Advancing to higher elevations
12 bird species
Britain
19 km northward average range extension
Red & Arctic Fox
Canada
Red fox replacing Arctic fox
Treeline
Europe, NZ
Advancing to higher altitude
Plants & invertebrates
Antarctica
Distribution changes
Zooplankton, fish &
invertebrates
California,
N. Atlantic
Increasing abundance of warm water spp.
Arctic shrubs
Walther et al., Ecological responses to recent climate change, Nature 416:389 (2002)
89
Red & Arctic Fox
90
91
Modes of Climate Variation
Periodicvariation
variation
Periodic
Abrupt shift in climate
state
Warming or cooling to new
climate state
Changes in amplitude or
frequency of climate
oscillations
92
The three serious problems
The three modern global change problems
discussed in this chapter-- global
warming, ozone depletion, or loss of
biodiversity
93
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
94
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.
95
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
96