How much can we change the Environment? n Locally – easy to see n Globally – do you believe it?...
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Transcript of How much can we change the Environment? n Locally – easy to see n Globally – do you believe it?...
How much can we change the Environment?How much can we change the Environment?
Locally – easy to see
Globally – do you believe it?– How many believe we, mere humans, can change the
climate?
– Can you give examples of any human / other life forms changing the climate of the earth?
Atmospheric Composition and ClimateAtmospheric Composition and Climate
Why do we worry about these simple stuff?– Evolution => Composition
– Composition => Thermal Structure
– Thermal Structure => Dynamics
The most basic question in the climate change debate is not whether the climate is changing, but are we changing the composition of the atmosphere, and hence the climate, too rapidly?
Evolution of the AtmosphereEvolution of the Atmosphere
“BIG BANG”
1. First atmosphere – one of cosmic gases: H2 - Hydrogen He - Helium
CH4 - Methane NH3- Ammonia
H2O - Water vapor CO2 - Carbon Dioxide
NOx - Oxides of Nitrogen
Evolution of the AtmosphereEvolution of the Atmosphere High temperatures probably drove off primeval
atmosphere.
Second Atmosphere: nothing -- similar to the moon, everything gone!
Third Atmosphere: developed from secondary sources such as outgassing from volcanoes, geysers, cracks, etc…
What is the current estimate of the Age of the Earth???
Evolution of the AtmosphereEvolution of the Atmosphere
H2Ov - 68%
After the Earth cooled
H2Ov - 15%
Composition ofVolcano Effluent
oceans
rainAs the earth cooled, the watervapor condensed and created
the oceans, etc.
First bacteria evolved maybe four billion years ago (anaerobic).
About 2-3 billion years ago green plants appeared in the oceans (algae). Why oceans?
Because liquid water (H2O) screens out ultraviolet radiation (UV).
Photosynthesis:
CO2 + sunlight + chlorophyll
O2 + organic material
Evolution of the AtmosphereEvolution of the Atmosphere
100 %
50 %
0%
Billions of years before present
5 3 2 1 0
CO2
O2
4
App
roxi
mat
e C
omp
ositi
on
Evolution of the AtmosphereEvolution of the Atmosphere There were no plants and animals on land until nearly
400 million years ago. Why?
Photodissociation by solar radiation
Photo-dissociationPhoto-dissociation Higher energy EM waves can “photodissociate,” or break
apart, certain larger molecules. UV radiation can photodissociate DNA molecules. Without protection from the atmosphere, life (as we know
it) could not live on land. What is the change that allowed the development of
terrestrial life?– UV radiation can also photodissociate other molecules such as
oxygen (formed via photosynthesis).
Timeline of Earth’s EvolutionTimeline of Earth’s Evolution
4.6 bya Formation of the Earth3.5 bya Abiotic synthesis, 3.2 bya Denitrification 2.3 bya Oxygen-producing photosynthesis by
cyanobacteriaStart of ozone formation
Evolution of the AtmosphereEvolution of the Atmosphere
4 Billion Years Ago
UV Radiation
Today
UV Radiation
Most of the UV radiation is screened from the earth’s surface, usually absorbed at altitudes above 20-40 km.
Chapman ProcessChapman Process
1. O2 + UV O + Oupper atmosphere
2. O2 + O + Body O3 + Body3-body production of ozone
3. O3 + UV O + O2
absorption of UV by ozone
4. O3 + O 2O2
removal process of ozone
Impact of above processes:– More oxygen, more ozone– Reduction of UV arriving lower atmosphere– Warming up of the middle atmosphere
Chapman ProcessChapman Process
High energy radiation
O2
concentration
Hei
ght
Ozone layerwarming in the
middle atmosphere
Ultraviolet RadiationUltraviolet Radiation
Evolution of the AtmosphereEvolution of the Atmosphere
Current Atmosphere
O2 21 % Increased via photosynthesis
Argon 1 % Increased via the radioactive decay of potassium ( K
)
CO2 0.03 % Decreased via photosynthesis
H2Ov 0 - 4 % Most variable component
also particulates and trace gases
N2 78 % Why ?
Evolution of the AtmosphereEvolution of the Atmosphere Why so much Nitrogen (78%)?
– Outgassing adds approximately 1 “unit”
– Lightning removes 4 to 10 units
– Nitrogen fixing by bacteria removes 20 to 100 units
– Anaerobic bacteria (probably in the oceans) adds the balance
Volcanoes
AnaerobicBacteria
Nitrogen FixingBacteria
Lightning
Earth
The Nitrogen in our atmosphere is primarily a result of thebalance of these four processes.
Timeline of Earth’s EvolutionTimeline of Earth’s Evolution
4.6 bya Formation of the Earth3.5 bya Abiotic synthesis, 3.2 bya Denitrification 2.3 bya Oxygen-producing photosynthesis by
cyanobacteriaStart of ozone formation
1.8 bya Nitrification (aerobic)1.5 bya Nitrogen fixation (aerobic)1.4 bya Earliest eukaryotes0.57 bya First shelled invertebrates0.43-0.5 bya Primitive fish0.395-0.43 bya First land plants -- oxygen and ozone
increase
Evolution of the Atmosphere (Summary)Evolution of the Atmosphere (Summary)
99 % of our present atmosphere is directly a result of life processes.
These life processes are primarily– Life cycles of nitrogen fixing bacteria
– Anaerobic bacteria
– Photosynthesis
Human can substantially impact the environment– CFC and Ozone Hole
Electromagnetic SpectrumElectromagnetic Spectrum
Black Body RadiationBlack Body Radiation
Stefan-Boltzmann’s Law of Black Body Radiation (1879/1884)
Wien’s Displacement Law (1894)
K)m(2898constantmax T
Peak wavelength of radiative emission for the sun and the earth?
Radiation Spectra
10-28
10-20
10-12
10-4
104
1012
1020
1028
1036
10-6 10-4 10-2 100 102 104 106 108 1010 1012
10-6 10-4 10-2 100 102 104 106 108 1010 1012R
adia
tion
int
ensi
ty (
W m
-2
m-1)
Wavelength (m)
60
00
K15
mil
lio
n K
Gam
ma X
UV
Vis
ible
Infr
ared
Sh
ort
rad
io
AM
rad
io
Lo
ng
rad
io
Tel
evis
ion
& F
M r
adio
30
0 K
1 K
Rad
iati
on in
tens
ity
(W m
-2
m-1)
Ultraviolet and Visible Spectra of the Sun
Figure 2.5
2 103
4 103
6 103
8 103
1 104
1.2 104
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Rad
iati
on in
tens
ity
(W m
-2
m-1)
Wavelength (m)
UV
-BU
V-A
Visible
FarUV
NearUV
Red
Green
Blue
Rad
iati
on in
tens
ity
(W m
-2
m-1)
Ultraviolet RadiationUltraviolet Radiation
Question: what would be the temperature of earth if there is no atmosphere?
Radiative EquilibriumRadiative Equilibrium
Solar radiation (r2) So ~ 1370 W m-2 Earth’s IR radiation (4r2
Radiative EquilibriumRadiative Equilibrium Fate of incident solar
radiation– 30 % reflected (albedo)
– 19 % absorbed by the atmosphere & clouds
– 51 % absorbed by the ground
Atmospheric OpacityAtmospheric Opacity
CO2, CH4, N2O, H2O…
Surface absorption
Solar shortwave Su
rfac
e lo
ngw
ave
Temperature increase
Greenhouse effect:Greenhouse gases absorbs longwave radiation from surface, making the atmosphere warmer. Without Greenhouse effect, temperature of earth is -18℃, not the current 15℃.
The Earth’s atmosphere is largely transparent to incident sunlight. It passes through and warms the surface of the Earth to a temperature of order 300 K.
Approximating the Earth as a blackbody and applying Wien’s Law, it’s easy to see that the Earth re-emits the energy at a wavelength = 3 x 106/300 = 104 nm, which is in the IR.
Carbon dioxide, it turns out, is an effective absorber of IR radiation. Therefore, solar energy is trapped in the Earth’s atmosphere. That’s good, because it moderates the climate.
Up to a point.
Increasing amounts of CO2 in the atmosphere trap increasing amounts of heat, leading to a global temperature increase. The consequences of can be catastrophic!
Planet Venus Earth Mars
CO2
96 bar
(96%)
1 bar
0.03%
0.007 bar
(95%)
Surface
Temperature450 C 15 C -55 C