1. Earth’s Climate & Mankind
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

2. 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
Decrease in Arctic sea ice cover from

3. How We Will Study Climate Change

4. Time Scales of Climate Change

5. 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

6. Earth’s Climate System and the Interactions of its Components

7. Forcing & Response

8. Climate Forcing Tectonic Processes
Slow movement of plates affects climate only very slowly

9. 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.

10. 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 ( ’s years)

11. 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.

12. 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

13. 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

15. Time Scale of Forcing vs. Response
Forcing is slow compared to response
Climate system tracks forcing
Typical of climate change on tectonic time scales

16. Time Scale of Forcing vs. Response
Forcing is fast compared to response
Little response to climate forcing
Stochastic events with short-lived response

17. 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

18. Cyclic Forcing and Response
Natural climate forcing may vary in a cyclic fashion producing cyclic response
Response time same; forcing is changing

19. 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

20. 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

21. 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

22. 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

23. 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

24. Response Rates & Interactions
What happens to air temperature near the foot of the glacier if incoming solar radiation were to slowly increase?

25. 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

26. 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

27. 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

28. 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