Download EARTH

Atmospheres
&
Global Warming
Earth and the Other Terrestrial Worlds
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;
Pressure pushes to poles
• Cold air moves from poles to
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
Earth’s Atmosphere
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Structure of Earth’s Atmosphere
 Pressure & density of decrease with altitude
 Temperature both increases and decreases with altitude
• Temperature domains define the major atmospheric layers

exosphere
• low density; fades into space

thermosphere
• temp begins to rise at the top

stratosphere
• UV light heats air (ozone absorbs it.)

troposphere
• layer closest to surface
• Convection heats air (rising hot air)
• temp drops with altitude
(mesosphere)
Stratosphere
Ozone Layer (absorbs UV)
Troposphere
Structure of Terrestrial Planet
Atmospheres
 Mars, Venus, Earth all
• have warm tropospheres
(and greenhouse gases)
• have warm thermospheres
which absorb Solar X rays
 Only Earth has
• a warm stratosphere
• an UV-absorbing gas (O3)
 All three planets have
warmer surface temps due
to greenhouse effect
CFCs Attack Ozone (O3)
The stratospheric ozone is an
environmental success story.
Scientists detected the declining
ozone in the atmosphere, collecting
the evidence that convinced
governments around the world to
take regulatory action.
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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.
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
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
How Greenhouse Gases Warm
the Troposphere
CO2
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Energy Balance
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%
Temperature vs Time
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1850
Year
2000
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CO2 Since the Year 1000 AD
CO2 in atmosphere, measured in thick arctic ice.
FAQ 2.1, Figure 1
Heat Content:
Increase in Atmosphere and
Ocean since 1945.
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CO2
Deuterium (hydrogen with a neutron)
Time (thousands of years before present)
Variations of deuterium (δD) in antarctic ice, which is a proxy for local
temperature, and the atmospheric concentrations of the greenhouse gases
carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) in air
trapped within the ice cores and from recent atmospheric measurements.
Data cover 650,000 years and the shaded bands indicate current and
previous interglacial warm periods.
Figure TS.6
Patterns of linear global temperature trends over the period 1979 to 2005 estimated at the surface (left), and for the troposphere
from satellite records (right). Grey indicates areas with incomplete data. (Bottom) Annual global mean temperatures (black dots)
with linear fits to the data. The left hand axis shows temperature anomalies relative to the 1961 to 1990 average and the right
hand axis shows estimated actual temperatures, both in °C. Linear trends are shown for the last 25 (yellow), 50 (orange), 100
(magenta) and 150 years (red). The smooth blue curve shows decadal variations (see Appendix 3.A), with the decadal 90% error
range shown as a pale blue band about that line. The total temperature increase from the period 1850 to 1899 to the period 2001
to 2005 is 0.76°C ± 0.19°C.
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Retreat of Glaciers
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1948
2002
2006
Trift Glacier, Gadmental,
Berner, Oberland Switzerland
Easton Glacier
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A 2003 photograph of the ~2.9 square kilometer Easton Glacier on Mount
Baker in Washington State. Between ~1890 and 1950, this glacier
retreated ~2400 meters. It subsequently expanded 600 meters during a
locally cold period between 1950 and 1979. Since then, it has again
retreated 315 meters (as of 2002) with 150 meters lost solely between
1997 and 2002.[1]. The extent of the glacier in 1985 is indicated in the
 Franz Josef
Glacier In Retreat
1939
1951
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1964
1960
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All survey regions except Scandinavia show a net
thinning. This widespread glacier retreat is generally
regarded as a sign of global warming. During this
period, 83% of surveyed glaciers showed thinning
with an average loss across all glaciers of 0.31 m/yr.
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
Is the Sun to Blame ?
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No. Luminosity has been constant.
(Solar max)
Percentage change in monthly values of the total solar irradiance composites of Willson and Mordvinov
(2003; WM2003, violet symbols and line) and Fröhlich and Lean (2004; FL2004, green solid line).
Sunlight hitting Earth:
• 11 year Sunspot cycle
• Offsets among instruments
• No trend
Global Warming

Made a political issue by certain people.
Three Facts are Absolute:
1.
2.
3.
Earth has warmed by 0.5 C 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
Only Question: Not Whether, but by how much are humans
contributing to Global Warming ?
Feedback Proceses:
Positive and Negative
Suppose Temp rises ==>
Evaporation of ocean water.
Feedback:
 H2O is a greenhouse gas ==>
Earth gets even Warmer !
 But clouds may form, increasing albedo.
==> Earth cools.
The Arctic:
Positive Feedback Process
 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 expand 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.
Consequences of
Global Warming
Consequences of Global Warming
According to UN report:
the world will be a much hotter place by 2100.
+2.4｡: Coral reefs almost extinct
In North America, a new dust-bowl brings deserts to life in the high
states, centeredd on Nebraska, but also wipes out agriculture and
ranching as sand dunes appear across five US states, from Texas
south to Montana in the north.Rising sea levels accelerate as the
Greenland ice sheet tips into irreversible melt, submerging atoll na
and low-lying deltas. In Peru, disappearing Andean glaciers mean
million people face water shortages. Warming seas wipe out the G
Barrier Reef and make coral reefs virtually extinct throughout the t
Predictions of temperatures
next 100 years
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DEPENDS ON MAGNITUDE OF FEEDBACK AND RATE OF INCREASE OF
GHG. IN 100 YEARS, FORCED CLIMATE CHANGE WILL MOST LIKELY
EXCEED NATURAL VARIABILITY
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 sign 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.
Stop Here.
Show: An Inconvenient Truth
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 Get DVD somewhere.
 Interesting Chapters:
 5-9, 11, 16-17, 20,
 21-28, 30-32
(or 5-9, 16-28)
Takes 30 min.
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
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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Magnetospheres
 The Sun ejects a stream of charged particles, called the
solar wind.
• it is mostly electrons, protons, and Helium nuclei
 Earth’s magnetic field attracts and diverts these charged
particles to its magnetic poles.
• the particles spiral along magnetic field lines and emit light
• this causes the aurora (aka northern & southern lights)
• this protective “bubble” is called the magnetosphere
 Other terrestrial worlds have no strong magnetic fields
• solar wind particles impact the exospheres of Venus & Mars
• solar wind particles impact the surfaces of Mercury & Moon
Earth’s Magnetosphere
Solar
Wind:
Electrons,
protons,
helium
nuclei
How Molecules Absorb Light
 X rays
• ionize atoms & molecules
• dissociate molecules
• absorbed by almost all gases
 Ultraviolet (UV)
• dissociate some molecules
• absorbed well by O3 & H2O
 Visible (V)
• passes right through gases
• some photons are scattered
 Infrared (IR)
• absorbed by greenhouse gases