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Class #39: Friday, April 17

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

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Class #39: Friday, April 17

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  1. Class #39: Friday, April 17 Mechanisms of Climate Change Natural and Anthropogenic Class #39: Friday, April 17

  2. 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 Class #39: Friday, April 17

  3. 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 Class #39: Friday, April 17

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  7. There may be a 26-million year periodicity in asteroid impacts Class #39: Friday, April 17

  8. The “Little Ice Age” occurred between about 1400 and 1850 Class #39: Friday, April 17

  9. 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 Class #39: Friday, April 17

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  11. 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 Class #39: Friday, April 17

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  15. 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 Class #39: Friday, April 17

  16. 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. Class #39: Friday, April 17

  17. 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 Class #39: Friday, April 17

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  25. 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 Class #39: Friday, April 17

  26. 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 Class #39: Friday, April 17

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