Transcript CO2 Variations, 1999 Mauna Loa, Hawaii

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
• rise and fall of temp
troposphere
• layer closest to surface
• temp drops with altitude
(mesosphere)
Stratosphere
Ozone Layer (absorbs UV)
Troposphere

Reasons for Atmospheric Structure
 Absorption of sunlight energy causes layering structure.
 Troposphere
• Air absorbs IR photons from the surface
• Hot air rises and high gas density causes storms (convection)
• Temperature drops with altitude
 Stratosphere
• Lies above the greenhouse gases (no IR absorption)
• Absorbs heat via Solar UV photons which dissociate ozone (O3)
• UV penetrates only top layer; hotter air is above colder air
 Thermosphere
• Absorbs heat via Solar X-rays which ionizes all gases
• Contains ionosphere, which reflects back human radio signals
 Exosphere
• Hottest layer; gas extremely rarified; provides noticeable drag on satellites
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
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%
Temperture vs Time
1850
Year
2000
CO2 Since the Year 1000 AD
CO2 in atmosphere, measured in thick arctic ice.
Heat Content:
Increase in Atmosphere and
Ocean since 1945.
Retreat of Glaciers
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1948
2002
2006
Trift Glacier, Gadmental,
Berner, Oberland Switzerland
 Franz Josef
Glacier In Retreat
1939
1951
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1964
1960
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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 ?
No. Luminosity has been constant.
W / m2
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Year
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 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.
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.
:
An Inconvenient Truth
Show the movie
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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
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