12 Paleoclimatology

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(12) Paleoclimatology

• Relevance and the ideal paleo record
• Methods used in reconstructing the past
• A brief history of the past 1,000,000 years
• (Principles of Climatology GEOG31064-Sheridan)

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Why study paleoclimatology?

• Understanding the past understanding the future
• Help improve climate models
• Understand what caused shifts in the past
• Understand how humans have influenced the climate
  system

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What methods do we use?

• Satellite
• Instrumental records
• Historical records
• Proxy records

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What makes an ideal paleo record?

• Quantitative measurement
• Global coverage
• Continuous record
• Small timescale

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Satellites

• First Microwave Sounding Unit (MSU) launched in
  late 1978
• Measurements of precipitation, water vapor,
  temperature, radiation balance
• Positives?
• Negatives?

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Instrument record

• How far back do instruments go?
• Wind vane 1500s
• Anemometer 1846
• Modern hygrometer 1820
• Thermometer 1600s
• Barometer 1643
• Rain gage 1442

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Problems with the data?

• Exposure!
• Accuracy warping glass
• Scales 77 temperature scales in use in 1792
• Spatial scale?
• What can go wrong with a temperature value over
  time?

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Reliable records

• CET (Central England Temperature) 1659
• London rainfall records 1697
• Reliable global records
• Temperature 1880
• Sea level 1900
• Surface ocean temperature 1930
• Atmospheric composition 1960

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Continuous historical records

• Weather diaries back to 1300s
• Fur-trading posts breakup of ice to 1600s
• Crop prices
• Japanese records of Cherry Blossom emergence to
  800

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Other historical records

• Nile floods go back to 622, intermittently to
  3000 BC
• Droughts, frosts, floods, heat waves
• Art and archaeology
• Problems?

11
Proxy records

• Use understanding of chemical, physical,
  biological processes to interpret climate
• Biological biogeography (organism range)
• Physical Physical processes (glacial deposition,
  isostatic rebound)
• Chemical isotopes

12
Sediments

• Continental location, carried to a quieter locale
  (usually under water)
• Interruptions?
• Land records 170My

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What is in the sediment

• Carbon decay (C14 to C12)
• Pollen and plant debris
• Animal (insect) remains
• Quantity of sediment

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Ice cores

• Continuous accrual up to 400,000 yr
• CO2 and CH4 trapped in ice
• O16 to O18 ratio

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Trees and corals

• Growth rates can be analyzed annually

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Questions

• A growing glacier is indicative of what?
• Is a sea-level rise the sea rising or the land
  sinking?
• Why did a tree not grow well?
• How spatially cohesive are the results?

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Climate history

• Early climate history warmer (more CO2)
• Always liquid H2O on the planet

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The past half million years
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Temp changes from LGM to today
Aug
Feb
20
Melting of the Laurentide
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Melting of the Laurentide
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Younger Dryas
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Circulation changes
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More recent shifts
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The Medieval Climate Optimum and the Little Ice
Age
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Central England Temperature record
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Causes of long term changes

• Continental shifts
• Atmospheric composition
• Solar variability
• Impacts of catastrophic events
• Orbital cycles