Planetary%20Energy%20Balance

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Planetary Energy Balance and Biogeochemical
Cycles
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Faint young Sun Paradox
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Post Main Sequence Stellar Evolution 4 H --gt 1 He
Log(Luminosity)
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Blackbody radiation
Solar flux is today F 3.7 x 107 W/m2
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Earths temperature depends (mainly) on three
things

1. Solar flux at 1 AU S 1370 W/m2
2. Earths albedo A (reflectivity) 0.3
3. Amount of warming due to atmosphere (greenhouse
   effect)

A fraction of sunlight reflected from a planet
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Planetary energy balance
Energy emitted by earth
Energy absorbed by earth

energy intercepted - energy reflected
?REarth2 S - ?REarth2 S A
?REarth2 S (1-A)
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Solve for Te 255 K brrrrr!
Earths temperature is 288 K. 33 K of greenhouse
warming!
But geological evidence for warm climate in
past!
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One layer atmosphere approximation
atmosphere
Earth
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Formaninifera (forams) single-celled protists,
some secrete CaCO3 shells
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All CO2 would be consumed in a few thousand years!
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Coincidence???
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Plate tectonics
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Why does plate tectonics occur?

• Mantle convection causes continental drift
• Subduction zones
• seafloor spreading at midocean ridge

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Volcanoes emit H2O and CO2 with small amounts of
N2, H2S, CH4 and SO2
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Subduction one plate being driven under another
(Cascadia subduction zone) Seafloor spreading
Creation of new seafloor crust as plates move
apart
Stratovolcano Composite volcano
Seafloor spreading
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H2O, CO2 gases from volcanoes
mantle
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Carbonate-silicate cycle stable over very long
periods of time but what if...?
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Changes in T, CO2 or H2O vapor
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What if the volcanism stopped?
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What if rain stopped?
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Early Earth No oxygen, methanogens
thrived! Today only anaerobic environments
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Long-Range Evolution of planetary atmospheres
H lost preferentially over O to space planets
oxidize over time
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Snowball Earth
The Earth experienced several episodes of GLOBAL
glaciation 750-580 million years ago, and 2-3
billion years ago Geological evidence for
glaciers at sea level, at the equator!
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During the Snowball Earth episodes, the normal
carbon cycle stopped. CO2 built up in the
atmosphere. Catastrophic warming followed.
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POSITIVE FEEDBACK Increasing glaciation caused
even more glaciation As Earth got whiter, it got
colder (reflecting sunlight away) How did we
ever snap out of it? Strange finding evidence
for a very WARM climate directly on top of the
snowball earth sediments!!
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A glacial dropstone in a banded iron formation
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During the Snowball Earth episodes, the normal
carbon cycle stopped. CO2 built up in the
atmosphere. Catastrophic warming followed.
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The Earth emerged from the Snowball episodes as
CO2 levels built up in the atmosphere The
response of climate to increasing CO2 levels is
not immediate. It takes about 400,000 years to
warm up. Geological evidence shows that the
Earth went into an extreme warming trend after
the Snowball episodes. How does CO2 warm the
Earth? It traps heat, like a greenhouse.
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• Carbon is either in the form of atmospheric gases
  (CO2 and CH4), both of which are greenhouse
  gases, or in solid materials (living things,
  fossil fuels, rocks)
• Processes that take carbon out of solids and put
  it into the atmosphere include
• volcanism
• loss of vegatation (deforestation)
• burning of fossil fuels

What is fossil fuel? Coal, oil, natural gas are
the remains of plants that lived millions of
years ago. Complex hydrocarbons that can be
burned, which releases CO2 CH4 2 O2 --gt CO2
2 H2O
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Positive and negative feedback loops