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The Greenhouse Effect
&
Global Warming
Earth and the Other Terrestrial Worlds
How do Greenhouse Gases
Make it Warmer?
CO
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Climate History of Venus
 Venus should have outgassed as much H2O as Earth.
• Early on, when the Sun was dimmer, Venus may have had oceans of
water
 Venus’ proximity to the Sun caused all H2O to evaporate.
•
•
•
•
H2O caused runaway greenhouse effect
surface heated to extreme temperature
CO2 released from rocks: Adds to greenhouse effect
UV photons from Sun dissociate H2O; H2 escapes, O is stripped
If Earth moved to
Venus’ Orbit
Venusian Weather Today
• Venus has no seasons to speak of.
• rotation axis is nearly 90º to the ecliptic plane
• Venus has little wind at its surface
• rotates very slowly, so there is no Coriolis effect
• The surface temperature stays constant all over Venus.
• thick atmosphere distributes heat via two large circulation cells
 There is no rain on the surface.
• it is too hot and Venus has almost no H2O
 Venusian clouds contain sulfuric acid!
• implies recent volcanic outgassing?
Mars’ Thin Atmosphere
 Martian sunset
illustrates just how thin
the Martian
atmosphere is.
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Martian Weather: N Polar Ice Cap &
Dust Storm
Martian Weather Today
• Seasons on Mars are more extreme than on Earth
• Mars’ orbit is more elliptical
• CO2 condenses & vaporizes at opposite poles
• changes in atmospheric pressure drive pole-to-pole winds
• sometimes cause huge dust storms
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 The last decade of the 20th
Century was the warmest in the
entire global instrumental
temperature record, starting in
the mid-1800’s.
 All 10 years rank among the 15
warmest, and include the 6
warmest years on record.
 Through the reconstruction of
past climate we can evaluate
the rarity and magnitude of this
warming.
Greenhouse Warming
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The Greenhouse Effect
Physics of Climate
Climate Forcing
Climate Change Response
Uncertainties
4.6 Billion Years Ago ...
Venus
Earth
Mars
SUN
0.7 AU
1 AU
(150 million km
from Sun)
1.5 AU
Temperature: Top of Atmosphere
decreases with distance from Sun
500
Temperature (Celsius)
500
400
Earth
-18oC (0oF)
300
300
200
100
Venus
100
0
Mars
0
0
0 AU
-100
-100
-100
5500 oC
0.2
0.4
0.6
0.8
Distance From Sun
1
1 AU
1.2
1.4
1.6
EARTH:
Surface
15oC (60oF)
Top of Atm:
-18oC (0oF)
Temperature (Celsius)
500
500
400
300
300
Surface
200
 All three
phases of water
100
100
0
0
0.5
No Greenhouse1
1.5
2
-100
-100
Surface warmer than top of atm  Greenhouse Effect
Clue: atm composition
Mass & Composition
of Atmospheres
n2
CO2: <0.04%
o2
co2
Earth
H2O: <4%h2o
CO2: 95%
O2: 21%
1
2
3
Venus: 95 atm
4
N2: 78%
Mars: 0.006 atm
Mars
n2
o2
Earth: 1 atm
co2
h2o
CO2
Greenhouse Warming
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Goldilocks and the Greenhouse Effect
Physics of Climate
Climate Forcing
Climate Change Response
Uncertainties
The Electromagnetic Spectrum
Wavelength l
 c = l x freq. = 3 x 108 m/s in vacuum
 Wavenumber = 1/ wavelength ( cm-1)
 Frequency in GHz (1 Hz = sec –1)
Energy
Vibrational Modes for CO2
n1
symmetric
n2
bending
15 mm
n2
asymmetric
4.3 mm
O
C
O
O
C
O
O
C
O
Greenhouse effect: Radiation at specific wavelengths
excite CO2 into higher energy states. Light energy is
absorbed by the CO2 molecules
Other Greenhouse Gases
O
H
O
H
O
O
ozone
water
H
N
O
N
H
C
H
H
nitrous oxide
methane
Absorption by different molecules
l = 0-15 µm
Absorption
CO2
Bending
Mode
Transmission
Peak terrestrial emission at ~300K
Earth Spectrum
Incoming from Sun:
High energy,
short wavelength
Top of Atm
Surface
0.5 mm
Theoretical Planck
curve T= 300 K
Infrared !
Radiance measured
At top of atm
20
Outgoing from Earth
Low energy
Long wavelength
10
Incoming Light: Peaks at 0.5 microns
Thermal Emission by Earth: Peaks at ~15 microns.
Energy Balance
Energy Balance at Top of Atmosphere:
Incoming shortwave = Outgoing longwave
Incoming Shortwave
absorbed:
Fo (1 – albedo)
High albedo:
Clouds (~10 mm), ice,
deserts
Outgoing longwave (IR)
radiation:
High clouds radiate less
due to lower Temp
Greenhouse Warming
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Goldilocks and the Greenhouse Effect
Physics of Climate
Climate Forcing
Climate Change Response
Uncertainties
Carbon Dioxide:
in our atmosphere is
Increasing rapidly
Worldwide CO2 Emission
By fuel type: 1970 - 2020
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Burning coal
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CO2 Causes Global Warming:
Stay tuned . . .
gasoline
Natural gas
Increase in Temperature tracks
Increase in Greenhouse Gases
Since 1850:
Atmospheric CO2 has
increased by 30%
Temperture vs Time
1850
Year
2000
Three Perspectives on
Global Warming
 Kyoto Protocol:
unfccc.int/resource/convkp.html
 White House Council on Environmental
Quality: www.whitehouse.gov/ceq
 Pew Center on Global Climate Change:
www.pewclimate.org
CO2 Since the Year 1000 AD
CO2 in atmosphere, measured in thick arctic ice.
Greenhouse Warming
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Goldilocks and the Greenhouse Effect
Physics of Climate
Climate Forcing
Climate Change Response
Uncertainties
Increase in both atm and
ocean heat content since
1945: unlikely caused by
natural variability and
redistribution of heat
Retreat of Glaciers
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1948
2002
2006
Trift Glacier, Gadmental,
Berner, Oberland Switzerland
1939
 Franz Josef
Glacier In Retreat
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1951
1964
1960
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Franz Joseph glacier
New Zealand
Length
Today
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Franz Joseph Glacier
New Zealand
Notice how the rock projecting
from the valley wall on the
left of the picture has been
smoothed and ground by
the glacier, which covered it
50 years ago, and for many
centuries before that.
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Longitudinal grooves in the
rock are characteristic of
glacial carving. Vegetation
has begun to cover it now
and the grooves are harder
to see than in 1964.
Receding Glaciers
Glacier
Length
(km)
South Cascade Glacier in
Washington. The yellow line
indicates the location of the
terminus in 1958. The red line
shows the position of the
terminus in 1998.
1500
2000
Temperature trend not
caused by solar
variability
Measurements of solar
irradiance:
•Solar-min solar-max cycle
•Offsets among instruments
•No trend
Global Warming
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Hot political issue.
More research needed on amount of warming caused by human production
of CO2.
Three Facts are Absolute:
1.
2.
3.
Earth has warmed by 0.5C in past 50 years. Temperature rise greatest in
past 10 years.
Humans are increasing by 30-50% the CO2 in the atmosphere.
Rising CO2 will cause rising temperatures
Key Question: How much are humans contributing to Global warming ?
Greenhouse Warming
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Goldilocks and the Greenhouse Effect
Physics of Climate
Climate Forcing
Climate Change Response
Uncertainties
Predicting Feedback
 Temp rise ==> Evaporation of ocean water.
 H2O is a greenhouse gas ==>
Earth gets even Warmer !
But clouds may form, increasing albedo.
==> Earth cools.
Difficulties in
Predicting Feedback
 Temp rise causes polar cap ice to melt.
 Artic ground exposed: dirt absorbs more
sunlight (lower albedo).
 Ground warms up more: Earth gets hotter.
 More polar cap ice melts. Earth gets even
hotter.
Consequences of
Global Warming
1. More evaporation of oceans: More storms,
and more severe storms.
2. Water in oceans exand with rising Temp.
Sea level has already risen 20 cm in past
100 years. Coastal regions and islands
flood.
3. Polar caps and Glaciers melt: Causes rising
ocean levels.
4. Change in ocean current patterns.
Desserts may get rain; Farmland may get
none.
By how much will temperatures change over
the next 100 years?
CO2 (t)
D T_surf
Different emission scenarios
DEPENDS ON MAGNITUDE OF FEEDBACK AND RATE OF INCREASE OF
GHG. IN 100 YEARS, FORCED CLIMATE CHANGE WILL MOST LIKELY
EXCEED NATURAL VARIABILITY
Global Climate Models used to project climate
change from different CO2 scenarios:
Business as
usual CO2
emission
Stabilization of
CO2
Control
Arctic is Warming at Twice Global Rate
The Arctic will lose 50% to 60% of its ice
distribution by 2100, according to the
average of five climate models run by
the scientists. One of the five models
predicts that it will no longer have any
ice in the summer.
Positive feedback. Snow and ice reflect
80% to 90% of solar radiation back into
space. But when these white surfaces
disappear, more solar radiation is
absorbed by the underlying land or sea
as heat. This heat, in turn, melts more
snow and ice.
The Kyoto Agreement
The Kyoto Protocol, negotiated by
more than 160 nations in 1997, will
reduce emissions of certain
greenhouse gases (primarily CO2).
Each of the participating developed
countries must decide how to meet
its respective reduction goal.
Signed by every country in the
European Union,
by Japan, and by Russia.
Kyoto Agreement:
The United States Won’t Sign
 In March 2001, President Bush announced that the
United States would not be a party to the Kyoto
Protocol on Global Climate Change.
 The Protocol requires signatories to cut carbon
dioxide emissions an average of 5 percent below
1990 levels between 2008 and 2012. Developing
nations are exempt from emission reductions.
 “President Bush strongly opposes any treaty or policy
that would cause the loss of a single American job, let
alone the nearly 5 million jobs Kyoto would have
cost.” - James Connaughton, chairman of the White House council
on Environmental Quality.
http://www.eia.doe.gov/oiaf/1605/vrrpt/summary/longform.html
United States Policy on CO2
“Voluntary Reductions”
Three Perspectives on
Global Warming
 Kyoto Protocol:
unfccc.int/resource/convkp.html
 White House Council on Environmental
Quality: www.whitehouse.gov/ceq
 Pew Center on Global Climate Change:
www.pewclimate.org
Marcy Stopped Here.
Ozone
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Ozone formation - ultra-violet
radiation from the sun (shown in
yellow) splits oxygen molecules into
oxygen atoms which then react with
more O2 to form ozone. Another
molecule (M) is needed to absorb
some of the huge amount of energy
involved in the reaction.
 Formation of ozone:
 Without ozone in the
sttratosphere, life would not
be possible on Earth.
 Ozone prevents harmful ultraviolet radiation from the Sun
(light with wavelengths less
than 320 nm) reaching the
ground.
 If allowed to reach Earth, this
radiation would severly
damage the cells that plants
and animals are made up of.
 Ozone was first formed in the
Earth's atmosphere after the
release of oxygen, between
2000 and 600 million years
before the first humans
appeared.
The Ozone Hole
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Oct 1998

Ozone also plays a very important,
natural role in the upper atmosphere
(the stratosphere). Ozone absorbs
harmful ultraviolet (UV) radiation from
the sun.

Reductions in ozone results in the
increase of harmful UV radiation
reaching the Earth's surface.
The biggest destroyer of the ozone in
the stratosphere is human produced
chemical compounds:
(chlorofluorocarbons - CFC's),

Earth radiance in the near
ultraviolet spectrum.
 More solar UV
light is reaching the
Earth over polar
regions.
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March 14, 2006
Ozone Layer:
Damage and Recovery
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In 1985 over 60 countries pledged to phased out a
group of chemicals called CFC's. These very stable
chemicals were once widely used in aerosols and
refrigerators. It was thought that their release into the
atmosphere produced chlorine radicals which reacted
with O3 to produce O2. The emission of CFC's into the
environment is now greatly reduced.
Human Activity Changes
Our Planet
 Ozone “hole” forming in the ozone layer
over the Antarctic.
 CFC (chlorofluorocarbons)
Cl-O
 International Treaties and policies:
Montreal protocol: phase out of production of CFC and
methyl bromide.
 Ozone hole will take decades to recover:
100 year lifetimes of CFCs in the atmosphere.
Recovery will be slow.
Habitat Destruction and Pollution
 Chemicals, such as pesticides, damage
reproduction of many species.
 Habitat is lost, such as wetlands and migration
paths over hundreds of miles.
 Extinctions occurring at high rates, compared
to historic averages.
What are Weather and Climate?
Weather – short-term changes in wind, clouds, temperature, and
pressure in an atmosphere at a given location
Climate – long-term average of the weather at a given location
 These are Earth’s global wind
patterns or circulation
• local weather systems move along
with them
• weather moves from W to E at
mid-latitudes in N hemisphere
 Two factors cause these patterns
• atmospheric heating
• planetary rotation
Global Wind Patterns
 Air heated more at equator
• warm air rises at equator;
heads for poles
• cold air moves towards
equator along the surface
 Two circulation cells are
created in each hemisphere
 Cells of air do not go directly from
pole to equator; air circulation is
diverted by…
 Coriolis effect
• moving objects veer right on a
surface rotating counterclockwise
• moving objects veer left on a
surface rotating clockwise
Global Wind Patterns
 On Earth, the Coriolis effect breaks each
circulation cell into three separate cells
• winds move either W to E or E to W
• Coriolis effect not strong on
Mars & Venus
• Mars is too small
• Venus rotates too slowly
• In thick Venusian atmosphere,
the pole-to-equator circulation
cells distribute heat efficiently
• surface temperature is
uniform all over the planet
Clouds, Rain and Snow
 Clouds strongly affect the surface conditions of a planet
• they increase its albedo, thus reflecting away more sunlight
• they provide rain and snow, which causes erosion
 Formation of rain and snow:
Four Major Factors that affect
Long-term Climate Change
Gain/Loss Processes of Atmospheric
Gas
 Unlike the Jovian planets, the terrestrials were too small to
capture significant gas from the Solar nebula.
• what gas they did capture was H & He, and it escaped
• present-day atmospheres must have formed at a later time
 Sources of atmospheric gas:
• outgassing – release of gas trapped in interior rock by volcanism
• evaporation/sublimation – surface liquids or ices turn to gas when
heated
• bombardment – micrometeorites, Solar wind particles, or highenergy photons blast atoms/molecules out of surface rock
 occurs only if the planet has no substantial atmosphere already
Gain/Loss Processes of Atmospheric
Gas
 Ways to lose atmospheric gas:
• condensation – gas turns into liquids or ices on the surface when
cooled
• chemical reactions – gas is bound into surface rocks or liquids
• stripping – gas is knocked out of the upper atmosphere by Solar
wind particles
• impacts – a comet/asteroid collision with a planet can blast
atmospheric gas into space
• thermal escape – lightweight gas molecules are lost to space when
they achieve escape velocity
gas is lost forever!
Origin of the Terrestrial Atmospheres
 Lack of magnetospheres on Venus & Mars made
stripping by the Solar wind significant.
• further loss of atmosphere on Mars
• dissociation of H2O, H2 thermally escapes on Venus
 Gas and liquid/ice exchange occurs through
condensation and evaporation/sublimation:
• on Earth with H2O
• on Mars with CO2
 Since Mercury & the Moon have no substantial
atmosphere, fast particles and high-energy photons
reach their surfaces
• bombardment creates a rarified exosphere
Climate History of Mars
• More than 3 billion years ago, Mars must have
had a thick CO2 atmosphere and a strong
greenhouse effect.
• the so-called “warm and wet period”
• Eventually CO2 was lost to space.
• some gas was lost to impacts
• cooling interior meant loss of magnetic field
• Solar wind stripping removed gas
 Greenhouse effect weakened until Mars froze.
Rock cycle
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Rock cycle
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Water cycle
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Residence time
 Average amount of time spent in a reservoir
Amount in/time
Amount in reservoir
Amount out/time
 Residence time =
amount in reservoir/amount added (removed) per unit
time
Residence time at Berkeley
 20,000 students
 5,000 enter (leave)/year
 Residence time?
Residence time = 20,000 students/5,000 students/year
= 4 years
Residence time of water in the
ocean
 Volume in ocean: 1.3x109 km3
 Discharge from rivers: 3.5x104 km3/yr
 Residence time: volume/discharge
= 1.3x109 km3/ 3.5x104 km3/yr
= 30 x 103 years
Carbon cycle
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Long term Carbon cycle
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Carbon cycle: volumes
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Earth’s Magnetosphere
Solar
Wind:
Electrons,
protons,
helium
nuclei