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MET 112 Global Climate Change Lecture 10

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Thawing Out the Earth. Restoring greenhouse gases to original levels is not sufficient ... Question: how much higher CO2 would be required to thaw out the earth? ... – PowerPoint PPT presentation

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Title: MET 112 Global Climate Change Lecture 10


1
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

2
Late Precambrian Climate Changes
  • Snowball Earth
  • Freeze-Fry Episodes

3
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.

4
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.

5
Freeze-Fry Episodes
  • A hypothesis that
  • Earth experienced
  • from very cold (Snowball Earth) to
  • Period of very hot temperatures
  • Many times back and forth!!

6
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!!

7
Time period
Cambrian Explosion
Freeze-Fry Episodes
8
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

9
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

10
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)

11
Before cooling
Reflection
Albedo
Incoming Sunlight
12
Before cooling
Reflection
Albedo 30
Incoming Sunlight
T 15C
13
After cooling
Reflection
Albedo
Incoming Sunlight
14
After cooling
Reflection
Albedo 60
Incoming Sunlight
T -50C
Now, restore greenhouse gases to original levels …
15
With Greenhouse Gases Restored
Reflection
Albedo
Incoming Sunlight
16
With Greenhouse Gases Restored
Temperature is not restored to original value!
Reflection
Albedo 60
Incoming Sunlight
T -40C
Planet is still frozen!
17
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?

18
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?

19
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?

20
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?

21
Excerpt from Scientific American Article
  • Evolution of a Snowball Earth

22
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)

23
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)

24
Warming (Continued)
  • After about 10 million years of warming, ice
    started to melt at the equator

25
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

26
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

27
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

28
Evidence for such an event
  • Layers of carbonate rocks found directly above
    glacial rock debris
  • Carbonate rocks are generally formed in warm
    oceans

29
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30
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

31
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.

32
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

33
Ice-Albedo Feedback (Cooling)
Initiating Mechanism
Earth Cools
Ice Coverage Increases
Albedo Increases
Absorption of Sunlight Decreases
34
Ice-Albedo Feedback (Cooling)
Initiating Mechanism
Earth Cools
Somehow this happens
Ice Coverage Increases
Positive Feedback
Albedo Increases
Absorption of Sunlight Decreases
35
Ice-Albedo Feedback (Warming)
Initiating Mechanism
Earth Warms
Ice Coverage
Albedo
Absorption of Sunlight
36
Ice-Albedo Feedback (Warming)
Initiating Mechanism
Earth Warms
Ice Coverage Decreases
Positive Feedback
Albedo Decreases
Absorption of Sunlight Increases
37
Water Vapor Feedback (Warming)
Initiating Mechanism
Earth Warms
Evaporation
Atmospheric Water Vapor Content
Greenhouse Effect
38
Water Vapor Feedback (Warming)
Initiating Mechanism
Earth Warms
Evaporation Increases
Positive Feedback
Atmospheric Water Vapor Content Increases
Greenhouse Effect Strengthens
39
Water Vapor Feedback (Cooling)
Initiating Mechanism
Earth Cools
Evaporation
Atmospheric Water Vapor Content
Greenhouse Effect
40
Water Vapor Feedback (Cooling)
Initiating Mechanism
Earth Cools
Evaporation Decreases
Positive Feedback
Atmospheric Water Vapor Content Decreases
Greenhouse Effect Weakens
41
Positive Feedback Exerted by Water Vapour in the
Atmosphere
42
Positive Feedback Exerted by Snow and Ice
43
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.

44
Possible Role of Cloud in Warming or Cooling the
Atmosphere
45
Possible Role of Cloud in Warming or Cooling the
Atmosphere
Positive Feedback
Negative Feedback
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