Controls on climate change:

• CO₂ content of the atmosphere and its long term controls
• Solar radiation changes and periodicities

Climate and the Seasons: the incoming energy

• Sun angle relationships:
• Sun directly overhead (90 degrees) - solar radiation per unit area is most concentrated
• At 45 degree angle 1 unit is spread out over 1.4 units of surface area (1/sin angle)
• At 30 degree angle 1 unit of incoming radiation is spread out over 2 units
• Sun angle - distance in the atmosphere the rays must travel

What causes the fluctuations in the sun angle at any given latitude

• Inclination of the Earth's axis of rotation
• Vertical rays of the Sun migrate from 23.5 dgrees North to 23.5 degrees South of the equator
• June 21-22 (summer solstice) the Sun is vertical at 23.5 N. Latitude
• Sun’s illumination reaches 23.5 degrees beyond the N. Pole
• December 21-22 (winter solstice) the Sun is vertical at 23.5 degrees S. Latitude
• Sun’s illumination reaches 23.5 degrees beyond the S. Pole
• In between, on March 21-22 and September 21-22 (vernal and autumnal equinoxes), the Sun strikes the earth vertically at the equator

Climatic history of the earth: Recent history

• Direct measurements - ~1880 to present
  • Annual mean temperatures since 1860
• Proxy Records:
  • Blooming of cherry trees in Kyoto since 800 AD
• Historical records:
  • Medieval Optimum - 900-1200 AD
  • Viking settlement of east Greenland, making wine in England
  • The Little Ice Age - 1500-1850 AD
  • Flemish paintings of frozen canals, advances of mountain glaciers
• General warming since 1850

Paleo-temperature Measurements:

• Oxygen isotope measurements: ¹⁶O = 99.8% of all oxygen; heavier ¹⁸O = 0.2%
• Difference in mass affects their behavior in evaporation, precipitation and incorporation into organisms
  • ¹⁸O/¹⁶O ratio is lower (i.e. water is richer in ¹⁶O) in water produced by evaporation--the lighter isotope is easier to evaporate than the heavier ¹⁸O. So, in times when lots of "light" water evaporated from the oceans is locked up in glaciers,
    • ice and glaciers lighter
    • ocean water heavier
  • The more ice on land, the heavier the ocean water is.

  ¹⁸O/¹⁶O ratio in skeletal remains of marine organisms reflects the temperature of surface ocean water

  Oxygen isotpe curves of the sediments give a continuous reading of the changing ice volume on the planet.
  
  

  background: a diatom (greatly magnified),
  a marine organism whose silicate exoskeleton
  can be used for oxygen-isotope studies.
  (as well as lots of other things.)
  
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