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Earth’s 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. Historical Examples of Climate Change?. Advance and retreat of glaciers

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Earth’s Climate & Mankind

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Earth’s 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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Earth’s Climate System

  • Earth’s climate system

    • Air, water, land and vegetation

  • Changes in Earth’s 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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Earth’s 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 earth’s orbit around the Sun affect the amount of solar radiation received on Earth’s 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 Earth’s surface. Can occur on long-term (100’s of millions of years) or on short-term (10-1000’s 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 Earth’s 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


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