1. Class #35: Friday, November 201 Past Climates: Proxy Data and Mechanisms of Change

2. Class #35: Friday, November 202

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4. 4 Glaciers, Icebergs, Bubbles, and Dust Climate clues buried in ice just as in lake sediments When snow and ice exceed melting, glaciers form. Ice crystals crush under pressure, trapped air expelled, and bubbles form Ice 30-m thick can flow downhill. At the coast, calving produces icebergs when the glacier breaks, with as much as 90% underwater Gas bubbles with CO 2 and CH 4

5. Class #35: Friday, November 205

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7. 7 Dust Dust in ice cores can be volcanic activity, or dry and windy conditions Acidic dust with sulfuric acid indicates volcanic activity Dust storms in Africa can be detected in polar ice cores

8. Class #35: Friday, November 208

9. 9 Marine sediments Current warmth on last slide is unusual Ratio of Oxygen-18 to Oxygen-16 in shells of marine animals tells about amount of continental ice that was present when they lived This method works back to 2-3 million years Warm periods about every 100,000 years

10. Class #35: Friday, November 2010 Fossil records are oldest Use Uranium dating for the oldest Types of plants and animals give climate clues Some plants live under very narrow conditions of temperature and humidity

11. Class #35: Friday, November 2011 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

12. Class #35: Friday, November 2012

13. Class #35: Friday, November 2013

14. Class #35: Friday, November 2014

15. Class #35: Friday, November 2015 There may be a 26-million year periodicity in asteroid impacts

16. Class #35: Friday, November 2016 The “Little Ice Age” occurred between about 1400 and 1850

17. Class #35: Friday, November 2017 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

18. Class #35: Friday, November 2018

19. Class #35: Friday, November 2019 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

20. Class #35: Friday, November 2020

21. Class #35: Friday, November 2021

22. Class #35: Friday, November 2022

23. Class #35: Friday, November 2023 Ocean circulation The thermohaline circulation is a world- wide 3-dimensional ocean circulation Sinking motion occurs in the North Atlantic when ice melts 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