Transcript Lecture 14: The Planets The Greenhouse Effect & Global Warming http://i.dailymail.co.uk/i/pix/2009/11/26/article-1231118-0 © 2005 Pearson Education Inc., publishing as Addison-Wesley.

Lecture 14:
The Planets
The Greenhouse Effect
&
Global Warming
http://i.dailymail.co.uk/i/pix/2009/11/26/article-1231118-0
© 2005 Pearson
Education Inc., publishing
as Addison-Wesley
Molecules in the Earth’s Atmosphere
 78% NITROGEN (N2)
O
 21% OXYGEN (O2)
• Produced by plants during photosynthesis
• Necessary for breathing by animals.
• Arrived 3.5 billion years ago: algae & bacteria
O
 ~1% ARGON (Ar)
O
C
O
 0.04% CARBON DIOXIDE (CO2)
•
•
•
•
© 2005 Pearson
Education Inc., publishing
as Addison-Wesley
Water vapor (H2O)
Carbon monoxide (CO)
Oxides of nitrogen
Methane (CH4)
Concentrations are a few
parts per million (ppm)
Water
Methane
Planet Earth:
4 Billion years of
a stable environment
Charles Keeling
1958
Mauna Loa,
Hawaii
Develops technique
for measuring
carbon dioxide in
the atmosphere.
A reduction in carbon dioxide occurs every spring and summer each year as
plant growth increased in the land-rich northern hemisphere, consuming CO2 by photosynthesis..
Arctic Ice:
Storing CO2 for 400,000 Years
Vostok ice core drilling site in Antarctica
The Vostok ice cores provide the
longest continuous record of
Antarctic climatic history. Cores go
to a depth of 3350 meters,
representing approximately
440,000 years of climate history.
Snow falls year after year, forming
stratified layers in ice. Trapped within
these layers are small air bubbles that
get trapped during snow falls. These
air bubbles contain samples of
atmospheric composition.
Cutting an ice core
to analyze the CO2
trapped inside.
CO2 Since the Year 1000 AD
CO2 in atmosphere, measured in thick arctic ice.
FAQ 2.1, Figure 1
Measuring Temperature of the Air:
Fractional Increase in Deuterium
Deuterium and 18Oxygen isotopes
Correlate with Air Temperature
Change
In
18O
Temperature (oC)
Earth’s Temperature Increased 0.9 C in the
Atmosphere and Ocean since 1880.
Figure TS.6
Global Averaged
Temperature
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.
Change in Temperature from 1960 to 2000
Increase in Temperature tracks
Increase in Greenhouse Gases
Temperature vs Time
CO2 vs Time
1850
2000
Year
Increase in Temperature tracks
Increase in Greenhouse Gases
During the past 400,000 years (from the Antarctic Ice cores)
CO2
(ppm)
TEMP
(oC)
Earth Data: CO2 and Temperature
Why is
Temperature
Correlated
with
CO2
What Determines a
Planet’s Surface Temperature?
 In the absence of the Greenhouse Effect, what
determines a planet’s surface temperature?
• The planet's distance from the Sun
• Luminosity of the Sun
• The planet’s overall reflectivity, “albedo” (fraction reflected):
- high albedo  less light absorbed planet cooler
 Earth’s average temperature would be
–17º C (–1º F) without the Greenhouse Effect !
Feedback: Declining Arctic Ice
Causes less reflectivity (Albedo)
How Greenhouse Gases
Warm the Atmosphere
CO2
The Greenhouse Effect
&
Global Warming
The Greenhouse Effect
 Visible Sunlight passes through the
Earth’s atmosphere.
 Light is absorbed by the surface.
 Surface warms. Emits its own light:
“thermal radiation”, as infrared (IR)
light - back out to space.
 IR light is absorbed by the
molecules and sent back to Earth !
 Result: the temperature is
higher than if there were no
atmosphere at all.
How do molecules
Absorb IR light?
Absorption of IR light by CO2
Vibrational Modes for CO2
n1
symmetric
n2
bending
absorb 15 mm
n
asymmetric
absorb 4.3 mm
O
C
O
O
C
O
O
C
O
Greenhouse effect caused by CO2:
CO2 molecules absorb infrared light at specific
wavelengths, trapping that energy in the Earth’s
atmosphere.
Other Greenhouse Gases
O
H
O
H
O
O
ozone
water
H
N
O
N
H
C
H
H
nitrous oxide
methane
These molecules in Earth’s atmosphere absorb IR light
Absorption by different molecules
l = 0-15 µm
Absorption
CO2
Bending
Mode
Transmission
Peak thermal emission at T=300K
Data
CO2 Levels are higher than in the past 400,000 years.
Temperature rose 0.9 C since 1860.
CO2 correlates with Temperature for 400,000 years.
Data: CO2 and Temp. are Rising.
Physics: Temp. Related to CO2,
by the Greenhouse Effect.
Global Warming Data
and Physics.
Is the Sun to Blame ?
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
Some say:
Global Warming
Is over.
Last Decade:
Little Temperature Change
Carbon Dioxide:
Humans are putting CO2
into our Atmosphere
Worldwide CO2 Production
By fuel type: 1970 - 2020
Burning coal
Gasoline
Natural gas
Fact, not speculation.
Glaciers are Retreating
Franz Josef Glacier
1939
1951
2011
1964
1960
Muir Glacier, Alaska
1941
2004
McCarty Glacier - Alaska
The Columbia Glacier in Alaska, seen in 2006 (top) and 2012 (bottom).
Retreat of Glaciers
1948
2002
2006
Trift Glacier, Gadmental,
Berner, Oberland Switzerland
Mt. Hood, Oregon
1984
2002
Easton Glacier
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
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.
Retreating Glaciers
Glacier Mass
http://www.climatechange2013.org/images/uploads/WGIAR5_WGI-12Doc2b_FinalDraft_Chapter01.pdf
Global Sea Level will rise
during the 21st Century
Expected Rise: 1-2 meters
Reasons:
- Melting of Arctic Ice
- Thermal expansion of ocean water
Global Warming

Certain people deny Global Warming is even happening !
Three Facts are Absolute:
1. Earth has warmed by 0.5 C in past 50 years.
Temperature rise greatest in past 10 years.
2. Humans are increasing by 30-50% the CO2 in the atmosphere.
3. Rising CO2 will cause rising temperatures
Solution:
1. Reduce use of fossil fuels: All Countries.
2. Find alternative Energy sources
3. Build Sea Walls
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.
Lecture 13: Atmospheres
The Greenhouse Effect
&
Global Warming
Section 4:
Comparison of Atmospheres:
Earth to Venus and Mars
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
Temperature (Celsiu)
decreases with distance from Sun
500
500
Temperature (C)
500
Earth
-18oC (0oF)
400
400
300
300
300
200
200
10
100
0
00
Venus
100
0
0
-100
-100
-100
0.2
0.4
0.6
0.8
1
Distance From Sun
1.2
1.4
Mars
1.6
Climate History of Venus
Venus outgassed as much H2O as Earth (similar planets).
•Early on, when the Sun was dimmer, Venus probably had oceans.
Venus’ proximity to the Sun caused H2O to vaporize.
• H2O vapor traps IR light from surface of planet
• 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. Water lost forever.
Suppose the
Earth moved to
Venus’Orbit
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
The Earth is Changing Rapidly
Who Speaks for Earth?
 CO2 is higher than at any time in recorded history.
 Global Temperatures are rising
 Humans are changing the planet Earth,
for the first time in history.
We don’t know the outcome of our experiment with our planet.
Maybe everything will be perfectly OK. But Venus offers pause.
Who is the steward, the
shepherd, the parent
of our home planet?
Show: An Inconvenient Truth
 Get DVD.
 Interesting Chapters:
 5-7-9, 11, 16, 20,
 21-28, 30-32
(or 5-9, 16-28)
Takes 30 min.
Martian Weather: N Polar Ice Cap &
Dust Storm