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New Readings

New Readings. They are all posted on the class web site. March 2: Reading 1-The last great warming March 12: Reading 2-Europe’s mild climate March 16: Reading 3-Shifting rain band March 26: Reading 4-Eurasian arctic during the last ice age

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New Readings

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  1. New Readings • They are all posted on the class web site. • March 2: Reading 1-The last great warming • March 12: Reading 2-Europe’s mild climate • March 16: Reading 3-Shifting rain band • March 26: Reading 4-Eurasian arctic during the last ice age • April 2: Reading 5-Did humans alter global climate • April 16: Reading 6-Unquiet ice

  2. The Greenhouse Climate

  3. We Know the Last 100 Myr Pretty Well… • Why? • Know • Continental Positon • Shape of the Ocean Basins • Temperature • Sea Levels

  4. Cretaceous: “abundance of chalk”

  5. Pangaea was breaking up….

  6. Sea Level was MUCH Higher….

  7. Climate Evidence • Warm-adapted vegetation and critters north of the Arctic circle • Brown-leaf evergreens • Turtles and crocodiles • No continental glaciation • Tropical conditions to 40 • Coral growing at the paleolatitude of New York • NO HARD Freezes in temperate latitudes.

  8. 180 Myr Ago

  9. 160 Myr Ago

  10. 120 Myr Ago

  11. 80 Myr Ago

  12. 60 Myr Ago

  13. Why so much warmer? • Climate models • Geography • CO2 4-6 times current levels • Ocean Circulation • Today the atmosphere transports about double the heat that the oceans transport • In Cretaceous that ratio was probably reversed

  14. CO2 probably drove the warming • Note that CO2 effect is not linear • At low levels snow and ice contribute to positive feedback • They reflect a lot of solar radiation back to space • At high levels there is much weaker effects • Little snow to melt • CO2 Saturation • But water vapor feedback works in the opposite direction

  15. Regression

  16. Transgression

  17. But what causes changes in sea level? • Changes in Climate • Ice vs no ice….about 50 meters of change in Cretaceous • Thermal contraction of water ~ 10 meters • Change in ocean basin volume • Spreading rates (50 to 150 meters) • Continental Collisions (~10 meters)

  18. Fast Spreading

  19. Slow Spreading

  20. What about rates? • Arguments about rates….

  21. Continental Collision • The size of continents effects the size of oceans (duh….) • The collision of India with Asia decreased the continental area by 2 million Km2 (and increased the oceans by that amount) • Net effect was about 10 meters of sea level drop

  22. Effects of Sea Level on Climate • Water has a large heat capacity and moderates regional climates • That’s why maritime (western ends of continents) climates tend to be milder • High stands of sea level extend the reach of maritime climates

  23. Climatic Factors • Ice Sheets • Antarctic ~ 66 meters of sea level rise • Greenland ~ 6 meters • Thermal Expansion/Contraction • The volume of water changes about 1 part in 7000 per degree C • Given ocean cooling since the cretaceous, that works out to about 7 meters of sea level drop.

  24. The 55 Myr Spike • We found this spike in the data….. • Increase in global temperatures of 5-9 C • Major acidification of the oceans • Extinction of about half of the forams • Why? • Major release of carbon • Methane on the seafloor

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