The Geologic Record

• Greenland Ice core - compared to continental
• Greenland Ice core - to 120,000 years ago
• Equatorial Pacific deep-sea core - present to 900,000 years ago
• Western Pacific deep-sea core - the record to 49 million years ago

Climate history in the older geologic record

• determinants of global climate
  • The amount of CO2 in the atmosphere
  • The amount of solar radiation reaching the surface of the earth
  • Latitude: location of the land masses and the oceanic conveyor belt
  • Elevation: Creation of high mountain chains where continental glaciers form
• Ice ages in the geologic record
• Glacial episodes since 2.3 b.y ago or perhaps longer
• Warm Cretaceous Period 115-135 million years ago
  • Coral reefs 5-15 degrees closer to the poles than today
  • Sea level was higher by 100-200 meters than today, no polar ice
  • Average global temperature 6-14° higher than today
  • CO2 released by superplumes - Ontong - Java volcanic plateau, twice as big as Alaska and about 40 km thick
  • originate at the core mantle boundary, link the core with the atmosphere
  • GCM models estimate of six time more CO2 than today

Cycles of climate change deduced from paleoclimate records

• Data from the Equatorial Pacific Core show cyclical changes
  • Most prominent is the near 100,000 year cycle
  • Less strongly defined cycles at 43,000, 24,000 and 14,000 years

Causes of long term climate change: Natural cycles termed Milankovich cycles

• Basic idea is that the energy input to the earth undergoes cyclical changes
• This is due to orbital parameters of the earth - the astronomical theory of climate change
• Components: obliquity of axis of rotation, ellipticity (eccentricity), and precession
• 40,000 years - axial tilt changes about 1.5 degrees
• 100,000 years - ellipticity: the earth was in a much more elliptic (less circular) orbit 100,000 years ago
• The axis of rotation wobbles like a spinning top - the poles trace a cone
  • The cone rotates once in 24,000 years
• variation of 10% radiation at any latitude in a given season
• Cumulative effect of orbital changes: curves combined look a lot like climate record

Amplification of temperature changes: positive feed backs

• Radiation changes alone cannot account for the 5-10° C temperature changes
• Milankovitch-enhancing processes
  • Amplification by changes in the atmosphere
  • Low greenhouse gases (e.g. CO2, CH4) in the atmosphere during glacial times
  • Dust in the atmosphere from ice cores
  • Reflectivity of large amounts of ice
  • Reduced thermohaline circulation: lessened production of dense water due to decrease in salinity

Predictions based on Milankovich Forcing

• The record of the past 150,000 years
• Changes to the present interglaciation

The overall climate system

• Involves all the subsystems
• All but the lithosphere are driven by solar energy
• Lithosphere driven by radioactive heat
• Responses in the atmosphere at a fast time scale
• Biosphere-atmosphere interactions on fast time scale
• Response in the oceans is on a slower time scale
• Great reservoir of heat energy
• Interactions with atmosphere in release of CO2
• Lithosphere slowest- position of land massses etc.