Earth

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Earths Climate Mankind

• Climate
• Long-term (years and longer) average condition of
  a region
• Rainfall or snowfall
• Snow and ice cover
• Temperature
• Weather
• Short-term (hours to weeks) fluctuations

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Historical Examples of Climate Change?

• Advance and retreat of glaciers
• Alpine glaciers shrunk in 20th century
• Thinning of ice on NW Greenland
• See Nature v. 414, 60-62
• Sea level rise
• El Nino/La Nina oscillations
• Length of growing season in Alaska increased from
  1950-2000
• Decrease in Arctic sea ice cover from 1970-2000

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How We Will Study Climate Change
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Time Scales of Climate Change
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Earths Climate System

• Earths climate system
• Air, water, land and vegetation
• Changes in Earths climate system
• Driven by cause and effect
• Buzz words of climate scientists forcing and
  response
• Forcing factors that drive or cause changes
• Response the climate change that occurs

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Earths Climate System and the Interactions of
its Components
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Forcing Response
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Climate Forcing

• Tectonic Processes
• Slow movement of plates affects climate only very
  slowly

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Climate Forcing

• Earth-Orbital Changes
• Variations in earths orbit around the Sun affect
  the amount of solar radiation received on Earths
  surface. Orbital scale changes occur over tens
  to hundreds of thousands of years.

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Climate Forcing

• Changes in the Strength of the Sun
• Affects the amount of solar radiation received on
  Earths surface. Can occur on long-term (100s
  of millions of years) or on short-term (10-1000s
  years)

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Climate Forcing

• Anthropogenic Forcing
• Not part of the natural climate system
• Affect of humans on climate
• Byproduct of agricultural, industrial and other
  human activities
• Example is addition materials to the atmosphere
  such as gases (CO2, N2O, etc.), sulfate particles
  and soot.

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Response Time

• Time it takes the climate system to react to a
  change in forcing (reaction time)

Response time amount of time it takes to get
50 of the way toward equilibrium
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Response Time

• Response curve exponential
• System moves ½ the way to equilibrium with each
  passage of response time
• Absolute amount of change decreases through time
  but proportional change towards equilibrium is
  constant

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Time Scale of Forcing vs. Response

• Forcing is slow compared to response
• Climate system tracks forcing
• Typical of climate change on tectonic time scales

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Time Scale of Forcing vs. Response

• Forcing is fast compared to response
• Little response to climate forcing
• Stochastic events with short-lived response

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Time Scale of Forcing vs. Response

• Time scale of forcing response time
• Yields dynamic and realistic response

Frequency of forcing has a direct effect on the
magnitude of the response
The time scale of forcing is not long enough to
allow the system to reach equilibrium
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Cyclic Forcing and Response

• Natural climate forcing may vary in a cyclic
  fashion producing cyclic response
• Response time same forcing is changing

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Cyclic Forcing and Response

• Since forcing is constantly changing, equilibrium
  value of system also changes
• Equilibration values set by the rate and
  direction of change of the forcing
• Regardless of the forcing rate of change
• Response rate of the system is is fastest when
  the system is furthest from equilibrium

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Cyclic Forcing and Response

• Frequency of forcing affects the amplitude of the
  response
• Slower cycling produces a larger response more
  time to react
• Faster cycling produces a smaller response less
  time to react

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Cyclic Forcing and Response

• Cycling forcing and response typical of
  Milankovitch type orbital cycles
• Changes in incoming solar radiation due to
  changes in Earths orbit occur cyclically over
  tens of thousands of years
• Response time of large glacial ice sheets also
  tens of thousands of years

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Response Rates Interactions

• Different components of the climate system have
  different response times
• Different components will respond to a change in
  forcing at different rates

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Response Rates Interactions

• If climate forcing occurs in cycles, it will
  produce different cyclic responses in the climate
  system
• Fast responses track forcing
• Slow responses lag forcing

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Response Rates Interactions

• What happens to air temperature near the foot of
  the glacier if incoming solar radiation were to
  slowly increase?

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Interactions in the Climate System

• Does the air warm due to increase in solar
  luminosity?
• Does the air stay cool because of the proximity
  to large mass of glacial ice?
• Response time of air influenced by both
• Response time of air will be faster than the
  response of the ice but lag behind forcing from
  the Sun

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Interactions in the Climate System

• Individual components within the climate system
  do not respond passively to forcing
• Dynamic interaction between systems
• Interaction blurs the distinction between forcing
  and response
• Difficult to determine what system or systems are
  reacting to the forcing

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Feedbacks in the Climate System

• Interactions can produce positive feedback
• Positive feedbacks produce additional climate
  change beyond that triggered by the initial
  forcing
• Positive feedback amplify changes

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Feedbacks in the Climate System

• Interactions can produce negative feedback
• Negative feedbacks reduce the response that would
  be caused by the forcing
• Negative feedback suppress climate change