class #39: friday, april 17
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Class #39: Friday, April 17. Mechanisms of Climate Change Natural and Anthropogenic. Review for test #4 on Monday, April 20. Chapter 13, Weather Forecasting Skip Boxes 13.2 and 13.4 Chapter 14, Past and Present Climates Chapter 15, Human Influences on Climate - PowerPoint PPT PresentationTRANSCRIPT
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Mechanisms of Climate Change
Natural and Anthropogenic
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Review for test #4 on Monday, April 20
• Chapter 13, Weather Forecasting– Skip Boxes 13.2 and 13.4
• Chapter 14, Past and Present Climates
• Chapter 15, Human Influences on Climate– No questions on ozone holes, pages 446-449
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What Mechanisms Have Caused Climate Change in the Past
• Overview: most sudden to the slowest• Volcanic eruptions: acidity, overall cooling• Asteroid impacts: overall cooling• Solar variability: cooling or warming• Variations in Earth’s orbit: Milankovitch cycles;
cooling or warming• Plate tectonics• Changes in ocean circulation: can be rapid and
long-lasting• Natural variability: variations without forcing
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There may be a 26-million year periodicity in asteroid impacts
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The “Little Ice Age” occurred between about 1400 and 1850
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Milankovitch Cycles
• Precession, which is north star, 27,000 years• Obliquity, tilt 22-24.5º, 41,000 years• Eccentricity, more/less elliptical, 100,000 years• Cold periods 20, 60, 160 K years ago
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Plate Tectonics and Continental Drift
• Pangaea, one large tropical supercontinent, 300 million years ago
• 160-230 million years ago, a split occurred• Laurasia: Asia, Europe, North America• Gondwanaland: South America, Africa, India,
Australia, Antarctica• Collisions caused Himalayas, Rocky Mtns.• Maybe ice sheets when continents became less
tropical
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Ocean circulation
• The thermohaline circulation is a world-wide 3-dimensional ocean circulation
• Sinking motion occurs in the North Atlantic when cold salty water sinks
• This circulation can be cut off when melt causes water to be less dense and not sink
• Maybe responsible for cooling in a period of glacial melt
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Global Warming is a fact!!!
• Over the past 2 decades the global average surface temperature has increased noticeably.
• A trend involves a steady change in one direction—upward for global average temperature.
• Not every location and/or every region shows the identical pattern.
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More observations of global warming
• Widespread retreat of nonpolar glaciers
• Thinning of arctic sea ice
• Decreased N Hemisphere snow cover
• Increase of global mean sea level
• Longer growing season in NH
• Shortened duration of ice cover on NH lakes
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Feedback: change leads to change leads to more change
• Positive feedback mechanism: reinforces (enhances) the original trend (change)
• Negative feedback mechanism: damps out an existing trend (change)
• Example of a positive feedback mechanism: warming, evaporation, water vapor,
warming
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More climate feedback mechanisms
• Example of a negative feedback mechanism: warming, evaporation, water vapor, cloud, cooling
• Another positive feedback mechanism:– Called the ice/albedo feedback mechanism– Cooling, more ice, higher albedo, more cooling– Warming, less ice, lower albedo, more warming
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