Transcript Lecture 14: Atmospheres The Greenhouse Effect & Global Warming Section 1: Measurements of the Temperature and CO2 in the Earth’s atmosphere.

Lecture 14: Atmospheres
The Greenhouse Effect
&
Global Warming
Section 1:
Measurements of the Temperature and CO2
in the Earth’s atmosphere.
Global Temperature: Past 130 years
Average Temperature
during the 20th Century
The Greenhouse Effect:
Trapping IR Thermal Emission
from the planet
Questions:
•
•
•
•
•
What is the greenhouse effect?
What is the cold evidence for Global Warming?
What different types of data indicate Global Warming
Is it good, bad, or both . . .
How would planets be different without the
greenhouse effect?
• Compare the greenhouse effect on
Venus, Earth, and Mars.
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
Ice Cores:
Fractional Increase in Deuterium
Deuterium and 18Oxygen isotopes
Correlate with Air Temperature
Change
In
18O
Temperature (oC)
Temperature and CO2 concentration in the atmopshere
During the past 400,000 years (from the Antarctic Ice cores)
CO2
(ppm)
TEMP
(oC)
Variations of deuterium (δD) in antarctic ice, which is a proxy for local
temperature, and the atmospheric concentrations of the greenhouse gas
carbon dioxide (CO2). Note the correlation.
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
Since 1850:
Atmospheric CO2 has
increased by 25%
Temperature vs Time
1850
Year
2000
Earth Data: CO2 and Temperature
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.
Lecture 13: Atmospheres
The Greenhouse Effect
&
Global Warming
Section 3:
Glaciers are Retreating
Feedback Mechanisms of the Greenhouse Effect
Projections for the Future of our Atmosphere
1939
 Franz Josef
Glacier In Retreat
1951
1964
1960
Muir Glacier, Alaska
1941
2004
McCarty Glacier - Alaska
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
Lecture 13: Atmospheres
The Greenhouse Effect
&
Global Warming
Section 2:
The Physics of Infrared Absorption by Molecules
Earth Data: CO2 and Temperature
Why is Temperature closely related to 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
Light Absorbed by the Atmosphere
Percent Absorption
Absorption by gases
In the Earth’s Atmosphere
Absorption in the Earth's atmosphere (middle
panel) and the effect that this has on both solar
radiation and upgoing thermal radiation (top
panel). Individual absorption spectrum for major
greenhouse gases plus Rayleigh scattering are
shown in the lower panel.
Both the Earth and the Sun shine by thermal
emission of light. For the sun, these emissions
peak in the visible region and correspond to a
temperature of ~5500 K. Emissions from the
Earth vary following variations in temperature
across different locations and altitudes, but
always peak in the infrared. The Earth has an
average emission temperature of about 250 K (20 C).
The wavelengths of absorption bands are
determined by the chemical properties of the
gases present. Water vapor is the most
significant of these greenhouse gases, followed
by carbon dioxide.
Absorption by different molecules
l = 0-15 µm
Absorption
CO2
Bending
Mode
Transmission
Peak thermal emission at T=300K
How Greenhouse Gases Warm
the Troposphere
CO2
The Greenhouse Effect
 Visible Sunlight passes through a
planet’s atmosphere.
 Some of this light is absorbed by the
planet’s surface.
 Planet 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.
What Determines a Planet’s Surface
Temperature?
 Greenhouse Effect cannot change incoming Sunlight, so
it cannot change the total energy returned to space.
• it increases the energy (heat) trapped in lower atmosphere
• it works like a blanket
 In the absence of the Greenhouse Effect, what would
determine a planet’s surface temperature?
• the planet's distance from the Sun
• the planet’s overall reflectivity, “albedo” (fraction reflected)
• the higher the albedo, the less light absorbed, planet cooler
 Earth’s average temperature would be
–17º C (–1º F) without the Greenhouse Effect !
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.
Feedback: Declining Arctic Ice
Causes less reflectivity (Albedo)
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
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
According to the UN report:
The world will be a much hotter place by 2100.
Coral reefs almost extinct
In North America, a new dust-bowl brings deserts to life in the high plains states, centered on Nebraska, but also wipes out
agriculture andcattle ranching as sand dunes appear across five US states, from Texas in the south to Montana in the north.Rising
sea levels accelerate as the Greenland ice sheet tips into irreversible melt, submerging atoll nations and low-lying deltas. In Peru,
disappearing Andean glaciers mean 10 million people face water shortages. Warming seas wipe out the Great Barrier Reef and
make coral reefs virtually extinct throughout the tropics. Worldwide, a third of all species on the planet face extinction+3.4｡:
Rainforest turns to desert
The Amazonian rainforest burns in a firestorm of catastrophic ferocity, covering South America with ash and smoke. Once the
smoke clears, the interior of Brazil has become desert, and huge amounts of extra carbon have entered the atmosphere, further
boosting global warming. The entire Arctic ice-cap disappears in the summer months, leaving the North Pole ice-free for the first
time in 3 million years. Polar bears, walruses and ringed seals all go extinct. Water supplies run short in California as the Sierra
Nevada snowpack melts away. Tens of millions are displaced as the Kalahari desert expands across southern Africa.
Melting ice caps displace millions
Rapidly-rising temperatures in the Arctic put Siberian permafrost in the melt zone, releasing vast quantities of methane and CO2.
Global temperatures keep on rising rapidly in consequence. Melting ice-caps and sea level rises displace more than 100 million
people, particularly in Bangladesh, the Nile Delta and Shanghai. Heatwaves and drought make much of the sub-tropics
uninhabitable: large-scale migration even takes place within Europe, where deserts are growing in southern Spain, Italy and
Greece. More than half of wild species are wiped out, in the worst mass extinction since the end of the dinosaurs. Agriculture
collapses in Australia+5.4｡: Sea levels rise by five metresThe West Antarctic ice sheet breaks up, eventually adding another five
metres to global sea levels. If these temperatures are sustained, the entire planet will become ice-free, and sea
Predictions of temperatures
next 100 years
DEPENDS ON MAGNITUDE OF FEEDBACK AND RATE OF INCREASE OF
GHG. IN 100 YEARS, FORCED CLIMATE CHANGE WILL MOST LIKELY
EXCEED NATURAL VARIABILITY
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
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
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.
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?
Suggested Movie:
An Inconvenient Truth
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
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