Earth’s Climate & Mankind

1. 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

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 1950-2000 • Decrease in Arctic sea ice cover from 1970-2000

3. How We Will Study Climate Change

4. Time Scales of Climate Change

5. 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

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 (10-1000’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