Clues to Past Climates



-The study of changes in climate taken on the scale of the entire history of earth.

-Proxy: a source of climate information from natural archives which can be used to estimate climate conditions prior to the modern period.


So How exactly is it Measured?


Tree Rings

  • Each year, a tree adds a layer of wood
  • Trees grow more quickly when warm and moist=wider rings
  • Trees grow more slowly and when cold and dry=smaller rings


Coral Reefs

  • Corals add seasonal layers
  • Thickness of layers change due to a combination of temperature, water clarity, and nutrient availability
  • The higher the ratio of O18 to O16 in corals=colder temperature

Ice Cores

  • Layering thickness indicates the amount of precipitation
  • bubbles in ice are used to measure the composition of air
  • the higher the ratio of O18 to O16 in ice cores=warmer temperature
  • particles from volcanic ash or pollution indicate major historical events


  • may contain preserved plants, animals, or pollen, which can be characteristic of certain climates
  • High Mg/Ca ratio of preserved species=high temperature
  • Greater occurance of C13-O18 bonds=low temperature

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