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 Colour 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 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
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