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This class session focuses on the mechanisms of climate change, both natural and anthropogenic. Key topics include past and present climates, weather forecasting, and human influences on climate. Students will review significant environmental events such as volcanic eruptions, asteroid impacts, solar variability, and Milankovitch cycles. The session highlights the alarming trends in global warming, featuring evidence like glacier retreat and rising sea levels. Additionally, it examines feedback mechanisms, including positive and negative feedback that contribute to climate changes.
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Class #39: Friday, April 17 Mechanisms of Climate Change Natural and Anthropogenic Class #39: Friday, April 17
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
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
There may be a 26-million year periodicity in asteroid impacts Class #39: Friday, April 17
The “Little Ice Age” occurred between about 1400 and 1850 Class #39: Friday, April 17
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
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
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
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
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
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
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
