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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
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
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
earth s climate system
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
climate forcing
Climate Forcing
  • Tectonic Processes
    • Slow movement of plates affects climate only very slowly
climate forcing9
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.
climate forcing10
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)
climate forcing11
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.
response time
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

response time13
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
time scale of forcing vs response
Time Scale of Forcing vs. Response
  • Forcing is slow compared to response
    • Climate system tracks forcing
    • Typical of climate change on tectonic time scales
time scale of forcing vs response16
Time Scale of Forcing vs. Response
  • Forcing is fast compared to response
    • Little response to climate forcing
    • Stochastic events with short-lived response
time scale of forcing vs response17
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


The time scale of

forcing is not long

enough to allow the

system to reach


cyclic forcing and response
Cyclic Forcing and Response
  • Natural climate forcing may vary in a cyclic fashion producing cyclic response
  • Response time same; forcing is changing
cyclic forcing and response19
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
cyclic forcing and response20
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
cyclic forcing and response21
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
response rates interactions
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
response rates interactions23
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
response rates interactions24
Response Rates & Interactions
  • What happens to air temperature near the foot of the glacier if incoming solar radiation were to slowly increase?
interactions in the climate system
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
interactions in the climate system26
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
feedbacks in the climate system
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
feedbacks in the climate system28
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