Earth's Atmosphere
• Today we will talk about the part of Earth that
is most important to our survival - the
atmosphere
• Earth's atmosphere is unique in the Solar
System and has changed greatly over time
• Recent changes may be leading to global
warming and an increased threat to life on
Earth
Atmospheric Layers
• _
• As altitude increases,
pressure decreases and
the air becomes 'thinner'
• Surprisingly, temperature
does not constantly
decrease, but fluctuates
throughout the different
layers
Atmospheric Layers
•
The troposphere is the lowest
layer, rising to ~12 km above the
surface with decreasing
temperature
•
Temperature increases through
the stratosphere up to ~45 km
above the surface (airplanes fly
in the lower stratosphere)
•
_
•
The last layer is the ionosphere,
where sunlight breaks up
molecules/atoms and increases
the temperature slightly
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The Troposphere
•
The troposphere is the layer in
which we live
•
_
•
All weather on the Earth is
caused by convection
•
Hot air near the surface rises,
cools at higher altitudes, then
falls back
•
This circulation produces
wind, thunderstorms, weather
fronts, hurricanes, etc.
The Ozone Layer
• Ozone is simply 3 oxygen
atoms joined together (O3)
• This molecule is found in
abundance at the bottom of
the mesosphere
• _
• This protective layer
prevents most UV light from
reaching the surface
Destruction of the Ozone
•
Manmade chlorofluorocarbons
(CFC's) are present in some
aerosol sprays and refrigeration
equipment (freon)
•
_
•
Chlorine atoms are highly
reactive with ozone, and they
steal away an oxygen atom
•
Eventually, the chlorine-oxygen
molecule reacts with another
oxygen, leaving the chlorine
atom to break up more ozone
While O3 blocks UV light, O2 does not,
creating a hole in the protective layer.
One chlorine atom can break up
100,000 ozone molecules!
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Banning CFC's
• In the late 80's and 90's, many nations
agreed to begin phasing out CFC's from
many of their products
• Progress has been made, but it will take
decades to eliminate all CFC's from the
atmosphere
• _
Why is the Sky Blue?
•
The sun emits all colors from red to
blue, so why does the sky appear
blue?
•
When sunlight hits our atmosphere,
the gas and dust scatter some of
the light
•
_
•
This means the bluer light gets
spread over the entire sky, while
the redder light comes directly from
the Sun
•
Note that when the Sun is low in
the sky, the light is passing through
much more atmosphere and even
the red light becomes scattered
This type of scattering is known as
Rayleigh scattering.
Evolution of Our Atmosphere
• The primary (first) atmosphere of the
Earth would have consisted mainly
of the elements found in the solar
nebula, like hydrogen and helium
• _
• The secondary atmosphere of the
Earth was formed when volcanic
activity released carbon dioxide,
sulfur dioxide, and nitrogen
compounds into the atmosphere
3
Evolution of Our Atmosphere
• Many of the nitrogen
compounds were broken up
by UV light, leaving lots of
atmospheric nitrogen
• Other compounds, like CO2
and SO2, became trapped in
the Earth's surface or in the
oceans
• _
Natural Greenhouse Effect
• Outside the effects of man, there
have always been natural
amounts of greenhouse gases
like CO2 and water vapor in the
atmosphere
• Remember, greenhouse gases
block infrared radiation from
escaping into space, increasing
the temperature at the planet's
surface
Earth without greenhouse effect:
-23oC or -9oF
Earth with greenhouse effect:
22oC or 72oF
• _
Runaway Greenhouse Effect
• We have already seen on Venus
how the greenhouse effect can
scorch a planet if taken too far
• _
• The hotter the planet, the more
CO2 is released from rocks,
tundra, and the ocean
• Ice reflects more light than water as more ice melts, the Earth
absorbs more and more heat
4
Is It Real?
• We know how the
greenhouse effect works
and what causes it
Do you believe global warming is real?
40
35
• We know that runaway
greenhouse effect can
lead to increased global
temperatures
30
25
20
38
15
10
5
• What evidence is there
that global warming is
occurring?
1
0
YES
YES
NO
NO
Global Temperature
• We know that the Earth naturally undergoes warm and cool
periods (ice ages)
• From a variety of sources (tree rings, sediment layers,
isotope ratios in coral, etc.) we can trace temperature back
centuries
Recent Global Temperature
5
Is Global Warming Real?
• There are long term warming and cooling trends in
the past 2,000 years, as well as many sharp
increases and decreases
• However, the increase in temperature in the last 30
years is more drastic than any seen in the current
record
• Keep in mind that this is average global
temperature (it doesn't necessarily mean it will be
hotter everyday of the year where you live)
Are We Responsible?
• So we have established
that there is a recent
significant increase in
global temperatures
Are humans the main cause?
40
35
30
• We only have a record of
~2,000 years, so this could
just be a large natural
warming trend
25
20
36
15
10
4
5
0
• Is there any evidence that
humans may be the cause
for the increased
temperatures?
YES
NO
Yes
No
CO2 in the Atmosphere
• Carbon dioxide is the most
common greenhouse gas
• The majority of the world's
energy comes from the
burning of fossil fuels
(coal, gas, oil) which
releases large amounts of
carbon dioxide
• Is the human contribution
enough to offset the global
balance?
6
CO2 in the Atmosphere
What happened
in world history
around this time?
Maybe a Natural Trend? - NO!
Need More Proof?
Human Population
CO2 Emissions
7
Are We the Main Cause?
• There is no doubt that since the industrial
revolution, there has been a major increase in the
amount of carbon dioxide in the atmosphere
• There is also no doubt that increased amounts of
CO2 in the atmosphere will produce an enhanced
greenhouse effect and increase temperatures on
the surface
• Put the two together ...
Will It Affect Us in Our Lifetimes?
• This is the most
controversial question we
have faced, as evidenced
by the quiz
Affect climate/world in our lifetime?
25
20
• Many would say small
effects can be seen
already
15
22
18
10
5
• But will major changes
occur in our lives?
0
YES
YES
NO
NO
– The answer shouldn't
matter ...
Glacial Melting
• Evidence for increased
temperatures are seen
around the world with
receding glaciers
• In the past 60 years (a
lifetime) many glaciers
have shrunken by miles in
size
• Glacier National Park has
gone from ~150 glaciers in
1850 to ~35 today
– There will be none left by
~2030
8
Arctic and Antarctic Ice
• The ice depth of the arctic is dropping rapidly (50% of the
ice gone by 2050's)
• Many cargo lines are planning to be able to cross ice-free
paths through the arctic in the summer in the next 10 years
-0.9m
-0.9m
-1.3m
-1.4m
-1.8m
-1.7m
Arctic and Antarctic Ice
• Ice at the south pole is melting at a drastic rate as well
• Changes in the amount and location of ice has a drastic
effect on a variety of species in these food chains
Larsen B ice shelf, 17th Feb 2002
Larsen B ice shelf, 5th March 2002
(16 days later)
Where Does All the Ice Go?
• The melting ice will eventually lead to large
changes in the global sea level
• The major sea currents (such as the Gulf
Stream) will become disrupted as the ice
disappears and water rises
• The less ice on the surface, the less
reflective the surface, and the heating
intensifies
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Global Sea Levels
Buoy depth over the past 200 years.
Changes in the Weather
• Remember that all weather
is tied to convection, which
is itself tied to the heating of
the Earth's surface
• As more heat becomes
available, more energetic
storms will be produced
(hurricanes, thunderstorms,
drought, wildfires, etc)
• There is much debate on
whether these changes are
already occurring
Changes in Economy
• Global warming is a lose-lose situation as far
as the world-wide economy is concerned
• Increased disasters and strain on natural
resources will cost governments an
increasing amount of money over time
• Any attempts to curb CO2 emissions will also
cost industrial nations greatly
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Changes in Health
• Climate change leads to a
change in the natural habitat
range for many disease
carrying insects (like
mosquitoes)
• Increased medical costs and
preparations strain nations
already financially burdened
• Undeveloped countries have
even less access to fresh,
clean water
Changes in Government
• A decrease in the amount of fertile land will cause
dramatic changes in global politics
• Some models show drought conditions will occur for
the majority of the Midwest, while former tundra in
Canada and Siberia will open up large tracts of
farming land
• When the food supply of a nation like America is
threatened, how far would we go?
Past the Point of No Return?
• There are many scientists who believe that
conditions will worsen severely over the next
100 years whether action is taken or not
• The current political climate is not favorable
for a worldwide commitment to curb global
warming
• It will be our generation who shoulders the
majority of the burden
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