MET 112 Global Climate Change Lecture 10

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MET 112 Global Climate Change - Lecture 10

• Freeze Fry Episodes
• of the Late Precambrian
• Eugene Cordero
• San Jose State University

• Outline
• Positive and negative feedbacks

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Late Precambrian Climate Changes

• Snowball Earth
• Freeze-Fry Episodes

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Snowball Earth

• A hypothetical state in which all surface water
  is frozen.
• Some geologists think it may actually have
  happened.
• Other scientists find the idea hard to support.
• Evidence
• Reference Hoffman and Schrags Scientific
  American Article.

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Snowball Earth

• A hypothetical state in which all surface water
  is frozen.
• Some geologists think it may actually have
  happened.
• Other scientists find the idea hard to support.
• Evidence Low-latitude, low-elevation glaciers
• Reference Hoffman and Schrags Scientific
  American Article.

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Freeze-Fry Episodes

• A hypothesis that
• Earth experienced
• from very cold (Snowball Earth) to
• Period of very hot temperatures
• Many times back and forth!!

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Freeze-Fry Episodes

• A hypothesis that
• Earth experienced high-amplitude temperature
  oscillations in the late Precambrian,
• from very cold (Snowball Earth) to
• Period of very hot temperatures
• Many times back and forth!!

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Time period
Cambrian Explosion
Freeze-Fry Episodes
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The Cooling Phase Outline of Theory

• Something happened to cause an imbalance in the
  long-term carbon cycle
• The Earth cooled
• Ice began to expand from the poles
• The
  , accelerating the cooling
• Evaporation decreased (due to cooling of oceans)
• Water vapor concentration decreased,
• This accelerated the cooling even more
• Ice continued to expand until Earth was frozen

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The Cooling Phase Outline of Theory

• Something happened to cause an imbalance in the
  long-term carbon cycle
• Atmospheric CO2 levels decreased
• The Earth cooled
• Ice began to expand from the poles
• The Earths albedo increased, accelerating the
  cooling
• Evaporation decreased (due to cooling of oceans)
• Water vapor concentration decreased, weakening
  the greenhouse effect
• This accelerated the cooling even more
• Ice continued to expand until Earth was frozen

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The Situation

• A snowball Earth would have a high albedo,
  perhaps as high as 60.
• It would be difficult to thaw out such a planet
  (see next slides)

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Before cooling
Reflection
Albedo
Incoming Sunlight
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Before cooling
Reflection
Albedo 30
Incoming Sunlight
T 15C
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After cooling
Reflection
Albedo
Incoming Sunlight
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After cooling
Reflection
Albedo 60
Incoming Sunlight
T -50C
Now, restore greenhouse gases to original levels
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With Greenhouse Gases Restored
Reflection
Albedo
Incoming Sunlight
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With Greenhouse Gases Restored
Temperature is not restored to original value!
Reflection
Albedo 60
Incoming Sunlight
T -40C
Planet is still frozen!
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Thawing Out the Earth

• Restoring greenhouse gases to original levels is
  not sufficient
• Much higher levels of CO2 would be required
• Question how much higher CO2 would be required
  to thaw out the earth?
• How could CO2 levels get so high?

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Thawing Out the Earth

• Restoring greenhouse gases to original levels is
  not sufficient
• Much higher levels of CO2 would be required
• Question how much higher CO2 would be required
  to thaw out the earth?
• CO2 levels would have to be 350 times current
  levels!
• How could CO2 levels get so high?

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Resolutions

• One possibility a large increase in volcanic
  eruptions over a long period
• Another possibility a decrease in
  silicate-to-carbonate conversion
• Why would this happen?

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Resolutions

• One possibility a large increase in volcanic
  eruptions over a long period
• Not likely
• Another possibility a decrease in
  silicate-to-carbonate conversion
• Why would this happen?

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Excerpt from Scientific American Article

• Evolution of a Snowball Earth

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The Warming Phase -- Outline

• The long-term carbon cycle became unbalanced in
  the opposite sense (more CO2 going into
  atmosphere than going out)
• Eventually, CO2 levels became very high
• Earth began to warm up
• Albedo decreased, accelerating the warming
• Evaporation increased, increasing water vapor
• Greenhouse effect became stronger, accelerating
  the warming
• (Continued)

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The Warming Phase -- Outline

• The long-term carbon cycle became unbalanced in
  the opposite sense (more CO2 going into
  atmosphere than going out)
• CO2 levels began to rise
• Eventually, CO2 levels became very high
• Earth began to warm up
• Ice began to melt near equator
• Albedo decreased, accelerating the warming
• Evaporation increased, increasing water vapor
• Greenhouse effect became stronger, accelerating
  the warming
• (Continued)

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Warming (Continued)

• After about 10 million years of warming, ice
  started to melt at the equator

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Warming (Continued)

• After about 10 million years of warming, ice
  started to melt at the equator
• Earth warmed very rapidly ice is completely
  gone in a century

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Getting Rid of the Excess CO2

• Now, atmosphere is incredibly hot (50C) because
  of high CO2 levels
• Hot oceans
• evaporation rate (globally)
• precipitation rate (globally)
• rates of chemical weathering
• rate of silicate-to-carbonate
  conversion
• Rapid removal of CO2 rapid formation of
  carbonate rocks

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Getting Rid of the Excess CO2

• Now, atmosphere is incredibly hot (50C) because
  of high CO2 levels
• Hot oceans
• High evaporation rate (globally)
• High precipitation rate (globally)
• High rates of chemical weathering
• High rate of silicate-to-carbonate conversion
• Rapid removal of CO2 rapid formation of
  carbonate rocks

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Evidence for such an event

• Layers of carbonate rocks found directly above
  glacial rock debris
• Carbonate rocks are generally formed in warm
  oceans

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Climate Feedbacks

• Earth/Atmosphere is delicate balance
• Slight changes in balance can cause
• These changes can be enhanced or diminished by
  positive or negative feedbacks
• Positive feedback
• Negative feedback

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Climate Feedbacks

• Earth/Atmosphere is delicate balance
• incoming and outgoing radiation
• Slight changes in balance can cause
• Large changes in global climate
• These changes can be enhanced or diminished by
  positive or negative feedbacks
• Positive feedback
• initial change reinforced by another process.
• Negative feedback
• initial change counteracted by another process.

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Positive Feedbacks

• Processes that accelerate a change
• Note Feedbacks cannot initiate change they can
  only alter the pace of change
• Important examples
• Ice-albedo feedback
• Water-vapor feedback

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Ice-Albedo Feedback (Cooling)
Initiating Mechanism
Earth Cools
Ice Coverage Increases
Albedo Increases
Absorption of Sunlight Decreases
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Ice-Albedo Feedback (Cooling)
Initiating Mechanism
Earth Cools
Somehow this happens
Ice Coverage Increases
Positive Feedback
Albedo Increases
Absorption of Sunlight Decreases
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Ice-Albedo Feedback (Warming)
Initiating Mechanism
Earth Warms
Ice Coverage
Albedo
Absorption of Sunlight
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Ice-Albedo Feedback (Warming)
Initiating Mechanism
Earth Warms
Ice Coverage Decreases
Positive Feedback
Albedo Decreases
Absorption of Sunlight Increases
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Water Vapor Feedback (Warming)
Initiating Mechanism
Earth Warms
Evaporation
Atmospheric Water Vapor Content
Greenhouse Effect
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Water Vapor Feedback (Warming)
Initiating Mechanism
Earth Warms
Evaporation Increases
Positive Feedback
Atmospheric Water Vapor Content Increases
Greenhouse Effect Strengthens
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Water Vapor Feedback (Cooling)
Initiating Mechanism
Earth Cools
Evaporation
Atmospheric Water Vapor Content
Greenhouse Effect
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Water Vapor Feedback (Cooling)
Initiating Mechanism
Earth Cools
Evaporation Decreases
Positive Feedback
Atmospheric Water Vapor Content Decreases
Greenhouse Effect Weakens
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Positive Feedback Exerted by Water Vapour in the
Atmosphere
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Positive Feedback Exerted by Snow and Ice
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Negative Feedbacks

• Processes that reduces an imposed change
• Important examples
• Cloud feedback
• Chemical weathering
• Reading
• http//www.doc.mmu.ac.uk/aric/gccsg/2-7.html
• Note Positive/negative feedbacks have no
  relation to good versus bad.

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Possible Role of Cloud in Warming or Cooling the
Atmosphere
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Possible Role of Cloud in Warming or Cooling the
Atmosphere
Positive Feedback
Negative Feedback