Transcript Class #34: Monday, April 7

Class #35: Friday, November 20
Past Climates: Proxy Data
and Mechanisms of Change
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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 CO2 and CH4
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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
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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
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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
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What Mechanisms Have Caused
Climate Change in the Past
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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
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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
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Ocean circulation
• The thermohaline circulation is a worldwide 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
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