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Discovering Past Climates

Discovering Past Climates. Tree Rings & Climate. Growth affected by: Temperature Rainfall T ree growth is indicated by the size & colour of rings Hold information for no more than a few hundred years (unless from an archaeological site). Analyzing Tree Rings . Width of the ring

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Discovering Past Climates

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  1. Discovering Past Climates

  2. Tree Rings & Climate • Growth affected by: • Temperature • Rainfall • Tree growth is indicated by the size & colour of rings • Hold information for no more than a few hundred years (unless from an archaeological site)

  3. Analyzing Tree Rings • Width of the ring • Wide ring indicates cool, wet weather - Rapid tree growth • Thin rings indicate dry, hot conditions - Growth is slower • Colour of the ring • Dark ring - Growth during late summer • Light ring - Growth during spring

  4. Ice Cores & Climate • Layers of ice & snow accumulate over the years • Ice cores (long cylinders of ice) are removed, using a drill • The extent of climate records depends on the depth of the ice core • EPICA (Antarctica) obtained climate records 800 000 years ago

  5. Evidence of Past Climates from Ice Cores • Ice is deposited annually when the summer melt is not enough to get rid of the winter’s snow • Ice cores hold 4 types of clues, which remain trapped until the ice melts • Dissolved particulate matter in the ice • Physical characteristics of the ice • Composition of trapped air bubbles • Composition of the ice

  6. Dissolved Particulate Matter in the Ice • Dust, ashes, salts, plant pollen & other matter are brought to Earth when it rains or snows • These samples, when frozen, give clues about events like: • Volcanic eruptions • Meteorite impacts • Forest fires • Vegetation cover

  7. Physical Characteristics of the Ice • Indicate the conditions of the temperature & humidity at the time the ice crystals formed • Snowflakes • Hail • Glaciers • Pack ice

  8. Composition of Trapped Air Bubbles • When water freezes, air bubbles of are trapped in the ice • Provides information on atmospheric composition when the ice was formed • Analysis of air at different depths in an ice core can help in tracking concentration of greenhouse gases change over hundreds of thousands of years

  9. Composition of the Ice • Isotopes: different atoms of a particular element that have same # of protons but different # of neutrons • Oxygen has 3 naturally occurring isotopes • Oxygen-16 • Oxygen-17 • Oxygen-18 • The difference in molecular weight affects the physical properties of water (freezing point) • Oxygen-18 freezes at a higher temperature than oxygen-16 • Oxygen-18 evaporates slower than oxygen-16 • Concentration of isotopes in different layers of ice tells us the temperature at the time the ice was formed • Ice that forms during high temperatures contains more oxygen-18 • During lower temperatures, polar ice contains less oxygen-18

  10. Oxygen Isotopes & Global Temperature

  11. How Scientists Determine Patterns of Climate Change

  12. Evidence of Past Climate Change from Sedimentary Rock • Sedimentary rock is formed over long periods of time from sediments of rock • The composition of the sediments provide evidence of past climate conditions • Pollen • Microscopic organisms • Shells

  13. Sedimentary Layers in Glacial Lakes • Sediment records reflect regularly repeating annual changes in sediment deposition • Sedimentary layers are called varves • Thick deposits of light-coloured sediment • Summer months • Fine, dark-coloured sediment • Winter months • Estimate rainfall & temperature over a long period of time

  14. Fossil and Preserved Organisms • Types and abundance of fossilized remains provide clues about past climate and environment

  15. How Scientists Infer the Rate of Climate Change

  16. Dendrochronology Activity

  17. Homework • Page 359 # 1, 2, 4 - 8

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