The Atmosphere
Composition
Chemically, the Earth’s
atmosphere is:
78% nitrogen
21% oxygen
1% argon.
Trace compounds,
like carbon dioxide,
comprise less than .1%
of the atmosphere.
Structure
90% of the
atmosphere lies
below this line
Because air is compressible, the pressure varies exponentially
with height (as opposed to linearly if it were not compressible).
Structure (cont.)
Temperature varies with height depending
upon the trace gases and type of radiation
present in the zone.
Thermosphere hotter at the top due to
friction with incoming solar particles
Stratosphere hotter at the top due to the
absorption of incoming UV by ozone
Troposphere hotter at the bottom due to
absorption of outgoing IR by greenhouse gases
Convection
Movement within the
atmosphere occurs because
of the differential heating
of the Earth’s surface by
the Sun.
Where the air is the hottest,
it expands the most and rises
higher into the atmosphere.
This causes cooler air to
rush in to replace it, creating
a convection cell.
On a non rotating Earth, this is an
idealized view of what that convection
might look like.
Coriolis Effect
On a non rotating Earth, all places
on the surface would have the same
horizontal velocity, i.e. no velocity.
Objects can change latitude without
having to change horizontal velocities
and still move in a straight path.
On a rotating Earth, objects at different
latitudes would have different horizontal
velocities. If an object does not change its
horizontal velocity as it changes latitude,
it will not appear to move in a straight path
from an Earth reference frame.
Coriolis Effect (cont.)
This film clip demonstrates that an
object that travels in a straight
path as seen from outside of the
rotating reference frame will
appear to travel in a curved path
while observed from within.
Effect on Weather Patterns
This effect prevents convective
cell winds originating at the
equator from reaching the pole,
and vice versa
Due to the Earth’s size and
rotation, this results in 3
different cells being formed in
each hemisphere
These cells help control the
climate of different regions by
by creating patterns of wind
and precipitation.
Isobars
Pressure systems drive
local wind. However,
the Coriolis effect means
that wind does not flow
directly from high to
low. In Northern
Hemisphere, wind is
deflected to the right
Thus, winds go in a
clockwise fashion around
high pressure and in counterclockwise fashion around lows
Winds attempt to go parallel
to isobars. The closer the
isobars are, the greater the wind
Global
Warming
Outline
GLOBAL WARMING:
Natural Greenhouse Effect
Global Warming
Controversy and GW
Possible effects of GW
Sun and earth
Sunlight warms Earth's surface
Heat radiates back
into atmosphere
Some heat reabsorbed
in atmosphere
Remainder radiates into
space
The Natural Greenhouse Effect
IT'S NOT BAD:
Heat trapping elevates temperature at Earth's surface
Makes Earth warmer than it would be without it
Allows liquid water to persist on the Earth's
surface without freezing
Presence of liquid water allowed for the evolution
of life
Natural G.H. Effect is necessary for life to persist
Wavelength and GH Effect
THE QUESTION:
But if the energy passed through the atmosphere on
the way to the Earth's surface, why does it get
trapped on the way out?
ANSWER:
The wavelength of the energy changes, and this is
the reason for the difference in entry and exit
To help you understand this, let's examine
wavelengths in more detail...
WAVELENGTH:
Electromagnetic radiation
(EMR) travels in waves
Wavelength (l): distance
from one wave crest to the
next
l
Shorter l = more energy
Fig. 3.7
Wien’s Law
Wien’s Law shows the relationship
between the temperature of an
object and the wavelength at which
the most energy is radiated.
For an object as hot as the Sun
(T = 6000 K), this translates into
a wavelength of .0000005 meters.
This is about the color yellow in
For the Earth (T = 300 K), this
the spectrum.
is a wavelength of .00001 meters.
This is the infrared part of the
spectrum.
Note
differences
in
wavelength
in incoming
and
outgoing
radiation
Fig. 3.8
Natural Greenhouse gases
Gases in atmosphere trap radiation at the long
wavelength of outgoing radiation, but not at the
short wavelength of incoming radiation
MOLECULES THAT TRAP HEAT IN G.H. EFFECT:
Water vapor & small droplets account
for 97% of the natural GH effect
H2
O
"Normal" levels of CO2 in
atmosphere also contribute
CO2
Absorbance by H2O
and CO2 is at l of
emitted radiation,
not incoming
Incoming W = 0.1 - 1.5 m
Fig. 21.8
So what's the problem?
HUMAN ACTIVITIES AFFECT SYSTEM:
Affect system so it traps more heat than it normally
would
This raises temperatures at the earth's surface
WHAT CAUSES THIS?
(1.) Increasing CO2 concentrations in atmosphere,
trapping more heat
(2.) Adding other gases ("greenhouse gases") to
atmosphere that also trap heat
Adding CO2: Human Impacts
WHAT ADDS CO2 TO THE ATMOSPHERE?
Burning fossil fuels for energy
Combustion of coal, oil, and
natural gas produces CO2
Overwhelms system's
capacity to remove CO2
from atmosphere
CO2 builds up, traps more
heat, temperatures
increase
Adding CO2: Human Impacts
COMPARING THE FOSSIL FUELS?
Which emits the least CO2 per unit energy produced?
Natural Gas:
Lowest CO2
Oil:
30% more CO2
than nat. gas
Coal:
43% more CO2
than nat. gas
CO2 concentrations since 1960
Fig. 21.9
Fig. 21.10
QUESTION:
Do increasing CO2
concentrations
correlate with higher
temps?
ANSWER:
Yes, historically. This
connection is
questioned by some
though
CO2: Deforestation
CO2 accumulates
because system can't
remove it fast enough
Why not?
Amazonian slash and burn agriculture
TROPICAL
DEFORESTATION:
Trees remove CO2 from atmosphere and store it in
their tissues. Deforestation (particularly in tropical
forests) decreases amount of CO2 removed.
Greenhouse gases
GLOBAL WARMING:
CO2 emissions account for 50-60% of the
anthropogenic (human-induced) temperature change
WHERE'S THE OTHER 40-50% FROM?
Other Greenhouse gases besides CO2 that trap heat
Chlorofluorocarbons (CFCs)
Methane (natural gas)
Nitrous Oxide (N2O)
CHLOROFLUOROCARBONS (CFCs):
15-25 % of anthropogenic GW due to CFCs
Used as coolants (freon), formerly as propellants
Atmospheric concentrations growing by 5% annually
METHANE (Natural Gas):
12-20 % of anthropogenic GW due to methane
From natural gas leaks, livestock
Concentrations currently stable, but high
NITROUS OXIDE (N2O):
5 % of anthropogenic GW due to N2O
From fertilizer use, burning coal, vehicle exhaust
Concentrations growing by 0.2% annually
Greenhouse gases
PROBLEM #1:
Compared to CO2 molecule, each molecule of these
gases traps:
CFCs: 1,500 - 7,000 times as much heat
Methane: 25 times as much heat
Nitrous Oxide: 230 times as much heat
PROBLEM #2:
Trap heat in a wavelength not trapped by CO2
Note 8-12 m window of absorbance Fig. 21.8
Recapping
NATURAL GREENHOUSE EFFECT:
Natural trapping of heat by gases in earth's atmos.
Allows life to persist on earth
GLOBAL WARMING:
Human activities accelerate heat trapping
Average global temperatures rise
Due to CO2 from fossil fuels, greenhouse gases
Global warming theory is controversial
Let's look at the controversy
Controversy #1:
Recent temp. change
RECORDED DATA:
Data only goes back to 1860
Since 1860, temps have risen about 0.9o F (0.5o C)
Recent years are warmest on record
THE CONTROVERSY:
Some claim temp. readings are inaccurate due to
"urban heat island effect", and temps. aren't really
rising
PROFESSOR’S OPINION:
Temp. increases since 1860 are real. Can correct for
urban heat island effect and also use satellite data
Controversy #2:
Correlation between CO2 and temp.
PAST CLIMATE:
Reconstruct past climate from air bubbles trapped in
glaciers. Finds CO2 levels and temp. to be correlated
THE CONTROVERSY:
CO2 data solid, but temp. estimates are suspect.
Contend there is no relation between CO2 levels and
temperatures
PROFESSOR’S OPINION:
Past estimates are estimates, but it does appear (and
makes sense) that CO2 levels and temp are related
Controversy #3:
Predicting temperature changes
CLIMATE MODELS:
Create model of earth's weather, input variables and
observe changes in the model. Suggests that
average temp. could rise 3.6o F (2.0o C) by 2100
THE CONTROVERSY:
Climate models highly speculative. Earth's climate
too complex to be modeled. Past models have been
wrong.
PROFESSOR’S OPINION:
Models are suspect, but they are getting better as we
learn more about how our atmosphere operates.
What's the consensus?
HUMAN vs. NATURAL:
Are current temp. increases human-induced or
natural?
Consensus: At least partly caused by human activities
HOW MUCH WILL IT INCREASE?
Consensus: Who knows? Earth's climate simply too
complex to be accurately modeled
Assuming temperatures rise as
expected, what would be the results?
Possible effects of global warming
SEA LEVELS RISE:
Rising temps. melt ice caps and
cause oceans to expand
Together these result in higher
sea levels
Could rise 19 in (48 cm) by 2100
Highly populated coastal areas become uninhabitable
Arable land decreases; less food production
Wealthy countries build dikes, poor countries flood
Possible effects of global warming
GRAIN BELT SHIFT:
Crops (corn, wheat, etc.) grow
optimally at temps in Midwest
U.S.
Midwest becomes warmer,
optimal temp. range shifts
northward
American breadbasket becomes
Canadian breadbasket
Global yields down 10-70%
Possible effects of global warming
EXTREME WEATHER:
Temperature drives weather
patterns
Higher average temps. means
more extreme weather (floods,
drought, high/low temps.)
Some are wondering if
current weather extremes are
due to climate change
Fig. 21.6
Ocean "conveyor belt" - could break down if
ocean temperatures elevate too much
What should we do now?
THREE SCHOOLS OF THOUGHT:
Nothing:
Contend GW is a hoax and overstated. No action is
necessary
Wait and see:
Need more definitive research to link human
activities with temperature increases. Study now
and act later.
Precautionary strategy:
Act now, while you have the chance. Research will
never prove connection, so why wait?
International treaties on GW
KYOTO, JAPAN (DEC. 1997)
Treaty calls for reductions in CO2, methane, nitrous
oxide, and three others that damage ozone
38 industrialized nations required to reduce their
emissions from 1990 levels by 2012.
E.U.  8%; U.S.  7%, Japan  6%
Developing countries, including China and India,
would have voluntary limits, no set standards
International treaties on GW
KYOTO, JAPAN (DEC. 1997)
Treaty needs congressional approval in U.S.
Will it ever pass?
Not very likely.
WHY?
Reductions cost money in short-term
Economy could suffer short-term
Global competitors like China have advantage
Political suicide for congressmen
Ozone Hole
For the last several decades, a
thinning of the stratospheric ozone
layer has been detected, most notably
over the Antarctic.
This is important, as stratospheric
ozone absorbs high energy UV
radiation, which has been linked
to skin cancer and crop failures.
This thinning is most likely due to CFC emissions, which
breakdown ozone.
CFC’s and Ozone
CFC is an extremely stable molecule.
In the upper stratosphere, UV radiation
breaks down CFC in chlorine and
other by-products
Free chlorine then breaks down ozone.
NOTE: CFC is also a greenhouse gas in the TROPOSPHERE. This
is the only relationship between ozone thinning and global warming,
i.e. GLOBAL WARMING AND OZONE HOLE ARE TWO
ENTIRELY DIFFERENT ISSUES!!!!
Other Pollutants
Sulfur dioxide (SO2) - reacts with water to produce sulfuric acid;
produced by burning coals and gas high in sulfur
Nitrogen oxides (NOx) - produces photochemical smog; reacts with
VOC’s to produce ground-level ozone; reacts with water to produce
nitric acid; produced by burning fossil fuels at high temperatures
Carbon monoxide (CO) - inhibits respiration; consumed in the
formation of ground-level ozone; produced by the incomplete
combustion of fossil fuels
Particulates - small particles (less than 2.5 m) cause lung damage
VOC’s - implicated in ground-level ozone; some are toxic and
cancer causing (benzene, MTBE, etc.)