Discovering Past Climates
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Transcript of Discovering Past Climates
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Discovering Past Climates
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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)
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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
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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
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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
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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
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Physical Characteristics of the Ice• Indicate the conditions
of the temperature & humidity at the time the ice crystals formed• Snowflakes• Hail• Glaciers• Pack ice
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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
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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
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Oxygen Isotopes & Global Temperature
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How Scientists Determine Patterns of Climate Change
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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
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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
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Fossil and Preserved Organisms• Types and abundance of fossilized remains provide clues
about past climate and environment
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How Scientists Infer the Rate of Climate Change
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Dendrochronology Activity
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Homework• Page 359 # 1, 2, 4 - 8