radiation_budget.ppt

Climate and Global Change Notes
13-1
Earth’s Radiation & Energy
Budget
Solar-Terrestrial Radiation Relationships
Interactions
Simple Radiation Budget
Shortwave Radiation Interaction with
Atmosphere
Blue Skies
Milky Skies
Red Sunsets
Shortwave Radiation Budget
Science Concepts
Reflection and Scattering
Absorption
Transmission
Scattering-Wavelength
Relationship
Atmospheric Gases
Clouds
Particulates
Absorption
Atmospheric Gases
Clouds
Transmission
Atmospheric Gases
Clouds
The Earth System (Kump, Kastin & Crane)
• Chap. 3 (pp. 50-51)
• Chap. 4 (pp. 58-59)

13-2
Earth’s Radiation Budget
http://www.cmdl.noaa.gov/
infodata/faq_cat-1.html
Science quotes of 5th
and 6th graders -
Most books now say
our sun is a star. But it
still knows how to
change back into a
sun in the daytime.
• Simple global radiation budget
- Radiation Balance
Incident solar radiation - Solar reflected radiation =
Earth’s emitted radiation
- Otherwise Earth would be warming or cooling
What happens to incident solar radiation as it interacts
with the Earth’s atmosphere? What are the three things that can
happen to radiation when it
interacts with an object?

13-3
Radiation
What happens to radiation when it interacts with an
object?
• Transmission - Energy passes through
material basically unchanged, i.e.,
unchanged energy and wavelength
- Note direction may be bent by
the process of refraction
• Reflection or scattering - Both redirect
radiation without changing the energy
or wavelength
- Scattering redirects radiation in all
directions, frequently has more intensity in some directions than other
- Reflection redirects radiation in a specific direction
• Absorption - Causes molecules to increase their kinetic energy, e.g., increase
http://rst.gsfc.nasa.gov/Intro/
Part2_3html.html

13-4
Solar or Shortwave Radiation
Solar
Radiation and
the Earth’s
Atmosphere
(Con’t)
• Why is the
sky blue?
• Why is the
cloud white?

13-5
Solar
Radiation
and the
Earth’s
Atmospher
e (Con’t)
• Why are
sunsets
and
sunrises
red?

13-6
Solar Radiation and the
Earth’s Atmosphere (Con’t)
• Why is the Earth white and blue?
• Why is the “sky” black?
Apollo 11 Earth View
• Earthrise viewed from lunar orbit
prior to landing
http://www.hq.nasa.gov/office/pao/History/
alsj/a11/AS11-44-6551.jpg

13-7
Solar Radiation and the Earth’s Atmosphere (Con’t)
Answer from 1/31/05 Parade newspaper insert
“The light that travels from the Sun to the Earth contains every color there is. But the
Earth’s air lets the blue light shine through the best. Sometimes, when the air is very
wet after it rains, it makes a rainbow, with all the colors. At sunset, red light can
shine through as well.”
Do you agree with this answer?
1/31/05 Parade newspaper insert, pp. 17-18.

13-8
Scattering by Atmospheric Gases
• Scattering redirects energy in all directions
• Scattering depends on the size of objects doing
scattering compared to the wavelength of
incident electromagnetic radiation
- For small objects, i.e., atmospheric gas
molecules that are about 1000 times smaller
than wavelengths of visible light
> Intensity of scattering (I), Rayleigh scattering, is inversely related
to the wavelength () of the radiation to the fourth power, i.e.,
I (scattering)  1 / 4
Shorter wavelengths are scattered more than longer wavelengths
Note: If the wavelength () of the incident radiation is halved, then
the scattered energy will 16 more
http://ww2010.atmos.uiuc.edu/(Gh)/
guides/mtr/opt/mch/sct.rxml

13-9
Scattering by Atmospheric Gases (Con’t)
• Scattering depends on the size of
objects doing scattering (Con’t)
- For small objects, i.e.,
atmospheric gases (Con’t)
> Examples:  (Violet) = 0.425 m,  (Blue) = 0.465 m and
 (Red) = 0.65 m
I (Violet) =  (Red) 4 = ( 0.65 ) 4 = 4.47
I (Red)  (Violet) 4 ( 0.425 ) 4
Violet scatters 4.47 times more than red; Blue scatters 3.76 times
more than red
> So why isn’t the sky violet?
Violet has an even shorter wavelength than blue, thus is scattered
even more than blue

13-10
• Scattering depends on
the size of objects doing
scattering (Con’t)
- For small objects,
i.e., atmospheric
gases (Con’t)
> So why isn’t
the sky
violet? (Con’t)
‡ Solar
radiation
has more
energy in
blue
wavelengths
than in violet
Wehrli, C., 1985: Extraterrestrial Solar Spectrum, Publication no.
615, Physikalisch-Meteorologisches Observatorium + World
Radiation Center (PMO/WRC) Davos Dorf, Switzerland.

13-11
http://www.croydonastro.org.uk/
Vision7-mod3.pdf
• Scattering depends on the size of objects
doing scattering (Con’t)
- For small objects (Con’t)
> So why isn’t the sky violet? (Con’t)
‡ Eye has two types of receptors,
cones and rods
‡ Cones - color vision, three kinds;
yellow-green (564 m), green
(534 m) and blue-violet
(420 m) (LMS cones)
§ Typically 64% of cones are
yellow-sensitive, ~32% green-
sensitive and ~2% blue-
sensitive
§ “Blue” cones are most
sensitive
§ Resulting eye sensitivity for
cones and rods - note rapid
decrease in sensitivity in violet
http://www.darksky.org/VisionSeries/vs2-4.html

13-12
http://www.darksky.org/
VisionSeries/vs2-4.html
• Scattering depends on the size of
object doing the scattering (Con’t)
- For small objects (Con’t)
> So why isn’t the sky violet? (Con’t)
‡ Rods
§ More cones than rods
§ More sensitive than cones
§ Not as color sensitive (only one type)
§ Function in less intense light than cones, helps with night vision
> Experiment - Look at a rose in full moonlight, the flower is brightly lit and
may even cast a shadow, but the red is gone, replaced by shades of
gray. In fact, the whole landscape is that way.
‡ Why? - Because of low light intensity, you are mainly seeing
with the rods which “see”
monochromatically,
i.e., little color
http://science.nasa.gov/headlines/y2006/
28sep_strangemoonlight.htm?list159742

13-13
Scattering by Atmospheric
Gases (Con’t)
• Apollo 11 Earth View
- No scattering of light at the
moon’s surface because the
moon has no atmosphere,
i.e., no gas molecules
http://www.hq.nasa.gov/office/pao/History/
alsj/a11/AS11-44-6551.jpg

13-14
> Red sunrises and sunsets
Axis of Rotation
Atmospheric Layer
Penetration
Depth
Solar
Rays
Solar
Rays
Penetration
Depth
Sunset

13-15
Scattering by
Atmospheric Gases
(Con’t)
• Lunar Eclipse
- Note Moon goes from bluish
white to reddish as
the lunar eclipse proceeds
and then back to bluish
white
- Result of solar radiation of
the Earth’s atmosphere
scattering blue more than
red light http://science.nasa.gov/
headlines/y2000/
ast02feb%5F1.htm

13-16
> The moon is not always at the same distance from the Earth and its
closer proximity causes it to look much larger
> We are looking horizontally through a thicker layer of the atmosphere,
rather than straight up through a thinner layer and thus the image of
the moon is magnified
> It is simply an illusion - the image is merely perceived as bigger when
the moon is near the horizon
How can we test these explanations?
Let’s think about how plausible each explanation might be and how we
might prove or disprove each one.
An Aside
• Why does the Moon appear so large when it is near the horizon?
- What are some plausible-sounding explanations?

13-17
> Facts: Apogee - 405,500 km; Mean - 384,400 km; Perigee - 363,300
km
> When the Moon is at apogee, it is 11% farther from Earth, 14% smaller
and 30% dimmer than it is at perigee
http://spaceweather.com/ 10/23/07 archive
Left - A big, bright perigee Moon Right - A lesser apogee Moon
An Aside (Con’t)
• The moon is not always at the same distance from the Earth and its
closer proximity causes it to look much larger
- Does the moon get farther away from the Earth as it rises?

13-18
An Aside (Con’t)
• It is simply an illusion: the image is merely perceived as bigger when
the moon is near the horizon Try the following experiment
- Try the following experiment - Look at the moon through a cardboard tube
(like those found inside rolls of paper towels). Viewing the moon this way
isolates it from the surrounding reference frame of trees and houses.
> Stand the cardboard tube on end and trace a circle around the base of
the tube onto a piece of paper
> Label the circle with the time of your observation
> Make your first observation of the moon when it is near the horizon.
Look at the moon through the cardboard tube and then make a sketch
in the circle you traced showing how much of the tube is filled by the
image of the moon
> Repeat the above steps every hour or two for about six hours (when
the moon is overhead)
> Compare your sketches and draw conclusions

13-19
An Aside (Con’t)
• Optical illusions
- Are the
yellow lines
the same
length?
http://news.bbc.co.uk/2
/hi/uk_news/magazine/
4619063.stm

13-20
Absorption by Atmospheric Gases
• Ozone and oxygen absorbs much of the ultraviolet in the upper atmosphere
• Water vapor and carbon dioxide absorb some of the near infrared
100
50
0.3 0.5 1.0 5.0 10.0 20.0
15.0
0
Wavelength (microns)
O2, CO2,
H2O
O3
O3
CO2
H2O
H2O
CO2,
H2O
Far Infrared
Near
IR
UV
Vis-
ible
Absorption
(%)
95% of
Solar
Radiation

13-21
Absorption by Atmospheric Gases (Con’t)
• Atmospheric absorption solar radiation

13-22
Absorption by Atmospheric Gases (Con’t)
• The atmosphere absorbs, transmits or reflects solar radiation
http://en.wikipedia.org/wiki/Image:MODIS_ATM_solar_irradiance.jpg

13-23
Interaction with Clouds
• Clouds, (typical droplets are about 50 times larger than
the wavelengths of visible light) when present they reflect,
absorb and transmit radiation.
- Clouds are very good reflectors of solar radiation.
Intensity of reflection related to the cloud depth
Cloud depth (m) Albedo (%)
100 75
1000 85
- Clouds are not very good absorbers of solar radiation. Amount of
absorption related to the cloud depth
Cloud depth (m) Absorption (%)
100 5
1000 10
Science quotes of 5th
and 6th graders -
I am not sure how
clouds get formed. But
the clouds know how
to do it, and that is the
important thing.

13-24
Interaction with Particulates
• Atmospheric particulates scatter radiation
- For larger objects (dust, pollution and droplets) intensity of scattering is
equal for all wavelengths, called Mie scattering. Causes haze, milky color
sky. Increases albedo.
• Example - Great Smoky Mountains
Clear Day Hazy Day
http://www.epa.gov/oar/vissibility/what.html
Particles such as sulfates, scatter more light, particularly during humid conditions.
Natural sources of haze-causing pollutants include dust, and soot from wildfires.
Manmade sources include vehicles, electric utility and industrial fuel burning, and
manufacturing. Some haze-causing particles are formed from gases emitted many
miles upwind.

13-25
What do we mean when we say “Once in a blue moon…”?
• According to modern folklore, a Blue Moon is the second full moon in a
calendar month. Usually months have only one full moon, but occasionally a
second one sneaks in.
- Full moons are separated by 29 days, while most months are 30 or 31
days long; so it is possible to fit two full moons in a single month
- This happens every two and a half years, on average.
> For example: July 2004 had one full moon on 2 July and another on
31 July which was by definition a Blue Moon
• Truly “blue” colored Moon’s can be cause by atmospheric particulates about 1
micron (near the size of red light scatter red light, while allowing other colors to
pass) in size, for example, volcanic ash or forest fires
- Blue Moon’s occurred in 1883 and for years after when Krakato erupted
- Other examples include
> El Chichon (1983) in Mexico
> Mt. St. Helens (1980) in U.S.
> Mount Pinatubo (1991) in Philippines
http://science.nasa.gov/headlines/
y2004/07jul_bluemoon.htm?list104690

13-26
Summary of Interaction with the Earth’s Atmosphere
• Most (55%) visible radiation or energy reaches the Earth’s surface.
Incoming Solar
Radiation 100%
Total Albedo 30%
3% Absorbed
by Clouds
16% Absorbed
by Air
4% Reflected
from Surface
20% Reflected
by Clouds
6% Scattered
by Air
25% Direct
26% Diffuse
51% Absorbed at the
Earth's Surface
Air here refers to the gas
molecules and particulates

13-27
Surface Albedo
• Uses MODIS data composited over a 16-day period, from April 7-22, 2002
• White indicates no data and no albedo data are provided over oceans
http://earthobservatory.nasa.gov/Newsroom/
NasaNews/2002/200207099816.html
Note: This is
surface albedo
Where are the
regions with the
highest albedo?
What type of
surfaces do
these regions
have?

13-28
Reflected Solar Radiation
Reflected Solar Radiation (W/m2)
Winter solstice, 22 December 2004
Summer solstice, 20 June 2005
NewImages/images.php3?img_id=17130
Note: These images are
top-of-atmosphere reflected
energy as seen by satellite,
not surface only reflected
energy
What dominates the albedo
in these images?

13-29
Budget
Shortwave Radiation Interaction with
Earth’s Surface
Surface Types
Soil Moisture and Vegetative Effects
Albedo
Water
Water and Land Differences
Science Concepts
Absorption
Energy Versus Temperature
Specific Heat
Absorption
Specific Heat
Mixing
Evaporation

13-30
Solar Radiation at the Earth
Surface
What happens to solar radiation as it interacts with the
Earth’s
surface?
• Absorbed or reflected
- Examples:
Albedo or
Material Absorption Reflection
Fresh Snow 25-5% 75-95%
Old Snow 60-30% 40-70%
Sea Ice 70-60% 30-40%
Desert 75-70% 25-30%
Glacier Ice 80-60% 20-40%
Grass 84-74% 16-26%
Crops 85-75% 15-25%
Deciduous Forest 85-80% 15-20%
Tundra 85-80% 15-20%
Soil 85% 15%
Water (Low Sun) 90-0% 10-100%*
Asphalt 94% 6%
Coniferous Forest 95-85% 5-15%
Water (High Sun) 97-90% 3-10%*
*albedo of water depends on the solar angle and sea surface roughness

13-31
Surface
Interaction with the Earth’s Surface
• What is wrong with this statement?
“Albedo was technically defined as the ratio of
electromagnetic energy reflected by a surface
to the amount of energy incident upon it. In terms
of the visible spectrum. it was a measure of how
‘shiny’ a surface was. A river had a high albedo,
since water reflected most of the sunlight striking it.
Vegetation absorbed light, and therefore had a low
albedo.”
“Congo” by Michael Crichton, p. 69. http://www.ucar.edu/communications/
CCSM/overview.html

13-32
Surface
Specific Heat Capacity
• Specific heat (heat capacity) is the amount of heat per unit mass required to
raise the temperature by one degree Kelvin or Celsius
- Coefficient which is related to how efficiently a material converts energy
into sensible temperature change
( Temperature change of object ) = ( Energy absorbed or given up by object )
( Object’s specific heat * Mass of object )
Specific Heat Capacity Specific Heat Capacity
Substance cal / (g K) Substance cal / (g K)
Water 1.00 Ice (@ 0°C) 0.48
Asphalt 0.22 Brick 0.20
Aluminum 0.22 Concrete 0.21
Copper 0.09 Glass (Typical) 0.20
Gold 0.03 Granite 0.19
Iron 0.11 Sand 0.20
Soil (Dry) 0.19 Soil (Typical) 0.25
Soil (Wet) 0.35 Wood (Typical) 0.40
Dry air (@ sea-level pressure) 0.24 Saturated air (@ sea-level pressure) 0.25

13-33
Surface
Interaction with the Earth’s Surface (Con’t)
• Example: Given one gram of material, what will be the temperature change if
one calorie of electromagnetic energy impinges on the material?
- Water - 90% absorbed, thus 0.9 cal of heat available to warm the water
Change in temperature
= Energy / ( Mass * Specific Heat )
= 0.9 cal / ( 1 g * 1 cal / g -°C )
= 0.9°C
- Soil - 85% absorbed, 0.85 cal of heat available to warm the soil
Change in temperature wet or dry
= 0.85 cal / ( 1 g * 0.35 or 0.19 cal / g -°C )
= 2.43 or 4.47°C
- Asphalt - 94% absorbed, 0.94 cal of heat available to warm the asphalt
Change in temperature
= 0.94 cal / ( 1 g * 0.22 cal / g -°C )
= 4.27°C

13-34
Surface
Interaction with the Earth’s Surface (Con’t)
• Why does land becomes hotter than water during the day?
- Water absorbs energy in a deeper layer, i.e., more mass because it is
more transparent
- Water has higher specific heat
- Water is a fluid and can mix the energy throughout a deeper layer
- More of the energy is used to
evaporate water over water
surfaces than over land surfaces
• Daily temperature range
Soil
Deep Circulating Pool
Pool 16" Deep
10 20 30 40 50
4
8
12
16
Temperature Range (°F)
Inches

13-35
Budget
Surface Budget
Surface Energy Budget
Fluxes
Bowen Ratio
Science Concepts
Conduction
Convection
Sensible Heat
Latent Heat
Radiation

13-36
Earth’s Surface Energy Budget
What happens to the energy absorbed at the Earth’s
surface?
• Conduction - Into ground
• Convection
- Important cause of weather
- About 20% of energy transfer
- Two types
> Sensible (Temperature change) - about 25%
> Latent (Evaporation) - about 75%
> The Bowen Ratio (BR) is the ratio of the sensible heating to latent
heating
Bowen Ratio = Sensible Heating
Latent Heating
Thus, the Earth’s average BR = 25% / 75% = 0.33

13-37
Energy Absorbed at the Earth’s Surface (Con’t)
• Convection (Con’t)
- Two types (Con’t)
> The Bowen Ratio (BR) varies depending on the surface type and
meteorological conditions
Geographical Area Bowen Ratio
Europe 0.62
Asia 1.14
North America 0.74
South America 0.56
Africa 1.61
Australia 2.18
Atlantic Ocean 0.11
Indian Ocean 0.09
Pacific Ocean 0.10
All land 0.96
All oceans 0.11
Note: Dry areas like Australia have high BR while wet areas like oceans have low
BRs, i.e., over dry areas, more energy is transferred from the surface to the
atmosphere via sensible heating while over wet areas, more energy is transferred to
the atmosphere via evaporation of water

13-38
> Examples:
1. Congo rain forest maximum
surface temperatures about 30°C
cooler than adjacent semiarid
lands
2. Dense irrigated poplar tree farm
(red) next to arid natural vegetation
in northeastern Oregon
http://www.agu.org/journals/eo/eo0643/
2006EO430002.pdf
Eos, Vol. 87, No. 43, 24 October 2006

13-39
> BR varies depending on soil
moisture availability
> Advanced Spaceborne Thermal
Emission and Reflection Radiometer
(ASTER) images on 8/27/06
‡ Top vegetation index, a
measure of plant density
§ Dense vegetation is dark
green
§ Sparse vegetation is pale
green
‡ Bottom is surface temperature
‡ Note contrast between irrigated
and non-irrigated land, irrigated
crop lands are much cooler,
30°C (54°F) cooler, than
surrounding native vegetation

13-40
> The Bowen
Ratio (BR)
Effect of soil
moisture on
maximum
temperatures
Eta model
volumetric
soil water
content (0-10
cm) over Northern
Alabama and
daily maximum temperature at Huntsville, AL

13-41
• Radiation
- Infrared (IR) or “Longwave” wavelengths
- Accounts for about 80% of energy transfer

13-42
Budget
Longwave Radiation’s Interaction with
Atmosphere
Greenhouse Gases
Longwave Radiation Budget
Science Concepts
Atmospheric Gases
Clouds
Absorption
Atmospheric Gases
Clouds
Transmission
Atmospheric Gases
Clouds

13-43
Earth or Longwave Radiation
What happens to “longwave” radiation emitted by Earth’s
surface?
• Absorbed, transmitted or
reflected by the atmosphere
- 5% transmitted
- 95% absorbed
• Absorbed by
“Greenhouse” gases
- Water Vapor
Absorption
(%)
0.1 0.3 0.5 0.7 1 5 10 15 20
0
50
100
Wavelength (micrometers)
Water
Vapor
95% of
Earth’s
Radiation

13-44
0.1 0.30.50.7 1 5 10 15 20
0
50
100 Carbon
Dioxide
0.1 0.30.50.7 1 5 10 15 20
0
50
100 Molecular
Oxygen
and Ozone
Interaction with Earth’s Atmosphere (Con’t)
Absorption
(%)
0.1 0.30.50.7 1 5 10 15 20
0
50
100
Methane
Absorption
(%)
0.1 0.30.50.7 1 5 10 15 20
0
50
100 Nitrous
Oxide

13-45
Interaction with Earth’s Atmosphere (Con’t)
• Absorbed by “Greenhouse” gases (Summary)
- “Atmospheric Window”
> 8-11 microns
100
50
0.3 0.5 1.0 5.0 10.0 20.0
15.0
0
Wavelength (microns)
O2, CO2,
H2O
O3
O3
CO2
H2O
H2O
CO2,
H2O
Far Infrared
Near
IR
UV
Vis-
ible
Absorption
(%)
95% of
Earth’s
Radiation

13-46
Interaction with Earth’s
Atmosphere (Con’t)
• Clear atmosphere absorbs
Earth’s radiation
Interaction with Clouds
• Liquid water (cloud droplets)
absorbs almost all IR (Infrared
or longwave radiation)
• Emit IR in all directions
depending on its temperature

13-47
Clouds and Radiation Budget
Effects of Clouds
• Reflect solar radiation
• Absorb longwave radiation
Net Effects of Clouds
• Deep, convective clouds
- Have tops that are highly reflective (high albedo) to solar shortwave
radiation - cooling effect
> However, because their tops are high, and thus cold, they emit little
longwave from their tops
- Bases readily absorb Earth’s longwave radiation - warming effect
- Net result is that deep, convective clouds have a neutral (neither
warming or cooling) effect on Earth’s climate system

13-48
Net Effects of Clouds (Con’t)
• Clouds (Con’t)
- High, thin cirrus clouds
> Mostly transparent (low
albedo) to solar
radiation
> Readily absorb Earth’s
longwave radiation
and emit longwave
in all directions, some
up and some down
> Net result is they warm
Earth’s climate system
- Low, thicker altostratus or
stratus clouds
> Highly reflective (high albedo) to solar
shortwave radiation
> Readily absorb Earth’s longwave radiation and emit longwave
in all directions, some up and some down
> Net result is that they cool the Earth’s climate system
Solar transmitted
Solar
transmitted
Surface
emitted IR
Surface
emitted IR
Cloud
emitted
IR
Cloud
emitted IR
Low Cloud
High Cloud
Cloud
reflected
solar
Cloud
reflected
solar
Cloud
emitted IR
Cloud
emitted IR

13-49
• Condensation trails
(Contrails)
- If air through which
the airplane is flying
is nearly saturated,
contrail will form
easier and last longer
than if the air is dry
- Lingering contrails
can spread out into a
cirrus layer of cirrus
- This MODIS image on
11/25/06 contains
scores of contrails
over the Midwest,
- Mingled contrails
have created a thick
cloud over the top
part of the scene (not all the clouds in the region are necessarily contrails)
- To the south, more distinct individual tracks are visible

13-50
• Condensation trails
(Contrails)
- Contrails can
influence the climate
by increasing the
cloud cover in heavy
air-traffic regions
- Recall thin cirrus
clouds cause
warming; their
thinness makes them
not very good solar
radiation absorbers,
but they do absorb
outgoing radiation
- NASA scientists have
discovered that
contrail-generated
cirrus clouds could be responsible for much of the warming of surface
temperatures over the U.S. from 1975-1994

13-51
• Reducing Night Flights May Ease Winter Global Warming, Report Says
Clouds of ice formed in the trails of jet exhaust trap heat and prevent the earth
from cooling. From the Los Angeles Times By Robert Lee Hotz, June 15, 2006
Contrails from winter night flights may be most responsible for the global warming caused by
air traffic, even though they constitute a fraction of commercial flights, meteorologists at the
University of Reading reported Wednesday.
Though there would be enormous practical problems, airlines could markedly reduce
aviation's impact on climate by changing schedules to restrict night flying, the researchers
said in the journal Nature. "We get one-half of the climate effect from one-quarter of the year,
from less than one-quarter of the air traffic," said meteorologist Nicola Stuber, who led the
English research team. "If you get rid of the night flights, you can reduce the climate warming
effect of the contrails."
Overall, aviation accounts for a relatively small portion of the emissions involved in rising
global temperatures, but international commercial air travel is among the fastest growing
unregulated sources of greenhouse gases and a topic of concern among climate regulators.
http://www.latimes.com/news/printedition/asection/
la-sci-nightfly15jun15,1,3604880.story?coll=la-news-a_section

13-52
• Reducing Night Flights May Ease Winter Global Warming, Report Says (Con’t)
By its accounting, the International Air Transport Assn. says that air traffic accounts for just
2% of global carbon dioxide emissions. Jet exhaust, however, injected at high altitude can
have two or three times the warming effect of carbon dioxide alone, researchers have
concluded.
In particular, climate experts have worried about the impact of the trails of ice particles that
quickly condense in the wake of jet exhaust, which can spread in hours from a few yards
wide to thousands of square miles. These shining clouds are mirrors in the sky. From their
upper surface, they reflect solar radiation, causing a slight cooling. At the same time, they
block any heat rising from the earth below, enhancing the greenhouse effect. At night, that
warming is especially pronounced, the researchers determined.
To explore the climate effects of contrails, Stuber and her colleagues studied the airspace
over the south of England at the entrance to the North Atlantic flight corridor, perhaps the
world's busiest skyway, with as many as 36,000 flights per month.They looked only at
information on contrails that persisted for an hour or more, combining aircraft flight data with
weather balloon recordings of temperature and humidity. Contrails were almost twice as
likely to form in winter as in summer.

13-53
• Reducing Night Flights May Ease Winter Global Warming, Report Says (Con’t)
Stuber determined that night flights accounted for 25% of the daily air traffic but contributed
60% to 80% of the climate effect. Moreover, winter flights accounted for 22% of the annual
total but contributed half of the annual warming.
"If we control emissions from other sources and don't do something about aircraft, then in the
future they are going to become a dominant source," said atmosphere expert Joyce E.
Penner at the University of Michigan. "Maybe there are ways to avoid such a high climate
impact by scheduling different routings."

13-54
• Clouds (Con’t)
- Clouds containing many
aerosols (left) also contain
many tiny water droplets
- Such clouds reflect light
(solar radiation) well
- Clouds containing fewer
aerosols (right) tend to
contain fewer and larger water droplets
- they transmit more solar energy to the Earth’s surface
http://science.nasa.gov/headlines/y2002/
22apr_ceres.htm?list104690

13-55
Earth Energy Budget
http://www.globalchange.umich.edu/globalchange1/
current/lectures/samson/global_warming_potential/
http://asd-www.larc.nasa.gov/ceres/
brochure/clouds_and_energy.html
Budgets
• Percentage • W / m2

13-56
Earth Energy Budget
http://asd-www.larc.nasa.gov/erbe/components2.gif
Budgets
• Percentage

13-57
Earth Energy Budget
Budgets
• Percentage
& W / m2
• Note numbers do not exactly match, but this depiction shows the greenhouse
effect
http://www.ngdc.noaa.gov/paleo/ctl/about4.html

13-58
Earth Energy Budget
Budgets
Surface (Watts m-2) Atmos.
Solar Earth Sensible Latent Solar Top of Atmos.
Source Rad. Rad. Heat Heat Absorb Albedo
National Acad. of Sciences (1975) 174 72 24 79 65 30
Paltridge & Platt (1976) 174 68 27 79 65 30
Budyko (1982) 157 52 17 88 81 30
MacCracken (1985) 157 51 24 82 79 31
Henderson-Sellers & 171 68 24 79 68 30
Robinson (1986)
Ramanathan (1987) 169 63 16 90 68 31
Schneiderf 154 55 17 82 86 30
Liou (1992) 151 51 21 79 89 30
Peixoto & Oort (1992) 171 68 21 82 68 30
Hartmann (1994) 171 72 17 82 68 30
Rossow & Zhang (1995) 165 46 66 33
Kiehl & Trenberth (1997) 168 66 24 78 67 31
Top of Atmosphere Incoming Solar radiation = 342 Watts m-2
Kiehl, J.T., and K.E. Trenberth, 1997: Earth’s annual global mean energy budget. Bull. Amer. Meteor.
Soc., 78, 197-208.

radiation_budget.ppt

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