Earth

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• Earths Climate System (part 1)
• climate system
• electromagenetic spectrum
• Earths radiation budget
• albedo
• greenhouse effect

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• Earths climate system
• climate driven by solar energy
• climate operates to distribute solar energy
• across surface
• Can ask
• Q1. What is solar energy?
• Q2. How does solar energy interact with planet?

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What is solar energy? -- electromagnetic
radiation (light) both a particle (photon) and
wave photons can have different energies
(wavelengths) high energies shorter
wavelengths low energies longer wavelengths
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Electromagnetic spectrum describes what light
of different wavelengths is called
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How does solar energy interact with planet? --
some is stopped by atmosphere, some is not --
depends on wavelength atmosphere transparent
for visible light, less so for other wavelengths
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Consider the transparency of Earths atmosphere
to light of (1) short wavelengths (2) medium
wavelengths (3) long wavelengths
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Short wavelengths a.k.a. shortwave radiation
transparency in Earths atmosphere very
low (shortwaves almost completely blocked)
UV Ozone layer
If not blocked, life as we know it wouldnt
exist on Earth -- cell damage!
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Medium wavelengths a.k.a. visible light
transparency in Earths atmosphere mostly high
(visible light mostly gets through, except when
cloudy)
If not transparent, life as we know it wouldnt
exist on Earth --too cold!
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Long wavelengths a.k.a. longwave radiation
transparency in Earths atmosphere somewhat
transparent (some longwaves get through, but not
all)
If not somewhat transparent, life as we know it
wouldnt exist on Earth -- too hot or cold!
(Greenhouse Effect)
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• Radiation budget
• describes inflow outflow of solar energy
• budget because energy is conserved

energy in energy used for warming
energy radiated back to space
-- most of the energy in is visible light --
energy radiated towards space is visible light
IR light
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Energy used for warming -- absorbed by
atmosphere -- absorbed by Earths
surface Energy radiated back to space --
reflected or scattered off of clouds or surface
70 of incoming 30 of incoming
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Energy in
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If sun overhead, get more photons concentrated in
a smaller area... more energy in
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Earths spin axis is inclined, so we get seasons
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Energy out is controlled by albedo
Albedo --the brightness of a surface can be
quantified 0 albedo 100
albedo --darkest surface --brightest surface
--all light absorbed --all light reflected
none reflected none absorbed
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energy in energy used for warming
energy radiated back to space
energy used for warming (100 - albedo)
energy radiated back to space albedo
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the amount of light absorbed depends on the
incident angle of sunlight
High incident angle
Albedo of water listed as 5-10 these diagrams
imply not always true
Low incident angle
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Energy radiated back to space -- reflected or
scattered off of clouds or surface
30 of incoming
If 30 of incoming solar energy is reflected
back to space, what does this say about the
overall average albedo of Earth?
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30 overall average
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Can have temperature- albedo feedback
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Can we have have temperature- albedo feedback if
the initial change is climate warming?
warming
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Can have temperature- vegetation- albedo feedback
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Energy used for warming -- absorbed by
atmosphere -- absorbed by Earths surface
70 of incoming
Visible light that is absorbed does two
things (1) it raises the temperature
directly (2) it is converted into lower
energy (infrared) light
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But recall that atmosphere is not completely
transparent to IR light ...this means that the
IR light cant be radiated back to space
easily ...so it becomes trapped
This leads to the Greenhouse Effect
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Greenhouse Effect
Visible light from the sun passes through the
atmosphere and warms the surface. Heat radiated
from the surface (infrared or IR light) travels
back out into space but is absorbed or deflected
back to the surface by certain gas molecules.
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Greenhouse Effect...
Trapped IR light warms the atmosphere, which
warms the surface. Temperature goes up
gradually.
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Greenhouse effect.
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Energy out
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Confusing!
Main point of this is that 95-96 of the IR
light radiated from the surface is trapped in the
atmosphere --warming it the Earths surface
X
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• Only some gases contribute to the Greenhouse
  Effect.
• N2 and O2 (the main constituents of our
  atmosphere) are not greenhouse gases.
• H2O, CFCs (chloroflourocarbons), CH4, CO2 are
  greenhouse gases and absorb IR light.
• SO2 is not a greenhouse gas. It combines with
  water to form H2SO4 (sulfuric acid) droplets.
  These droplets reflect incoming solar light back
  into space, resulting in planetary cooling.

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• Greenhouse gases.
• H2O is ubiquitous we cant control the amount
  of it in the atmosphere.
• CH4 is a fermentation product. Large amounts
  could be released from ocean (ice) deposits if
  the ocean warms.
• CFCs are largely man-made. International
  agreements in the 1970s limited their use,
  because of their harm to the ozone layer.

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• Greenhouse gases.
• CO2 is released by volcanoes.
• CO2 is produced by burning petroleum products
  and by burning trees. This can be controlled.

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Is the greenhouse effect all bad? No!

• It makes life as we know it possible on Earth.
• Earth gets about 31o C of greenhouse warming.
• Taverage 15 oC now, with Greenhouse Effect.
• Taverage 15 - 31 oC -16oC, without Greenhouse
  Effect.

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Climates on three planets
Venus Earth
Mars
avg. temp. 460 oC
15 oC -55 oC greenhouse
285 oC 31 oC 5 oC
warming avg. temp. 175 oC -16
oC -60 oC with no greenhouse

Just right
Too cold
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Climates on three planets
Venus Earth
Mars
greenhouse 285 oC 31 oC
5 oC warming atmosphere 96
CO2 77 N2 95 CO2
composition 3.5 N2 21 O2
2.7 N2 0.037 CO2
0.01 H2O
OK with
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CO2 abundance is rising in our atmosphere
10000 ppm 1 so 370 ppm 0.037
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CH4 abundance is also rising
1725 ppb 1.725 ppm 0.0001725
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Can have temperature- H2O vapor feedback possibly
also with CO2 and CH4
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