Fossils, Paleoclimate and Global Climate Change

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Fossils, Paleoclimateand Global Climate Change
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Global Warming

• CO2 levels in the atmosphere rising
• Average global temperature is rising
• Polar ice caps and mountain glaciers are
  shrinking
• Sea level is rising (transgression)
• Deserts are expanding
• Weather is getting more severe (?)

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Is this normal?

• How can we tell if the present change in climate
  is normal or not?
• Is the amount/rate of present climate change
  normal or is it extreme?
• Are humans responsible?
• Is there any way to answer these questions?

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Geologic Record

• Provides us with long-term perspective
• Contains indirect evidence of climate
• Contains direct evidence of climate
• Gives us a history of global climate change on a
  scale of millions of years to billions of years.
• Fossils are a key source of this information

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Indirect Evidence

• Evidence for
• Aridity
• Warm Climate
• Cold Climate
• Recorded by specific types of rocks

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Direct Evidence Ice Cores

• 100,000 years of continuous record
• Older than 100,000 is too distorted by plastic
  flow and mixing

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Data from Ice Cores

• Quantities of dust in each layer
• Related to wet vs. dry climate
• Air bubbles trapped in each layer
• Samples of ancient air
• Levels of CO2

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Sediment Cores

• Deep Sea Drilling Project (DSDP)
• Ocean Drilling Project (ODP)
• Integrated Ocean Drilling Program (IODP)
• Coring in lakes and bogs
• DSDP, ODP and IODP cores can extend back to Early
  to Middle Jurassic (approx. 180-200 Ma)

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Data from Sediment Cores

• Quantity of mud vs. shelly material
• Relates to sea level, climate and weathering on
  land
• Temperature proxies
• Chemical signatures
• Coiling in microfossils
• Chemical signatures from fossil shells

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Temperature Proxies Stable Isotopes

• Stable Isotopes are NOT radioactive
• Proportions of stable isotopes are dependent on
  temperature
• Ratio of 18O to 16O
• Ratio of 13C to 12C

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Stable Isotopes

• 18O is heavier than 16O
• Therefore it is harder to evaporate water with
  18O than normal water
• 18O is enriched in oceans especially when
  climate is cold
• 18O is depleted in atmosphere when climate is
  cold
• Therefore ice is depleted in 18O
• When climate is warmer, there is more 18O in
  atmosphere and therefore in ice
• Carbon isotopes follow similar trends

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What does theGeologic Record Tell Us?

• The normal climate of the past 1.0 billion
  years
• Warmer than present
• More uniform than present (less fluctuation)
• Past 20 million years have been highly variable
  and generally much colder

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Climate History20 Ma to Present

• 20 Ma climate was somewhat moderate
• Similar to present
• 5 Ma coldest climate of past 65 million years

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Pleistocene Epochthe Great Ice Ages

• 2.0 Ma to 10,000 years ago Pleistocene Epoch
• Four (or more) distinct episodes expansion and
  melting of ice sheets (continental glaciers)
• 12,000 10,000 Modern Climate sets in

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Recent Climate History

• 7000-6000 BP - Warm Peak
• 950-1300s Medieval Warm Spell
• 1300s Cool and Wet
• 1550 1850 Little Ice Age

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Food For Thought

• How many of the great events of recorded human
  history have been directly influenced by climate?

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Recent Climate History

• 7000-6000 BP - Warm Peak Great Ancient
  civilizations (e.g., Mesopotamia, Egypt)
• 950-1300s Medieval Warm Spell Rise of
  modern European nation-states
• 1300s Cool and Wet Bubonic Plague
• 1550 1850 Little Ice Age
• Washington crosses the Delaware
• Winter at Valley Forge

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So, are we to blame?

• Paleoclimatic record reveals major shifts in
  climate through time
• Is it coincidence or causation that climate is
  warming as we come out of last ice age?
• Is it coincidence or causation that industrial
  revolution falls within this same time?

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What factors cause changes in climate?

• Long term vs. short term changes
• Volcanic eruptions
• Earths orbital variations

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Why did the climate change so drastically and
repeadedly?

• Climate change and variations in Earths orbit
• Eccentricity elliptical to nearly circular
  cycles
• Obliquity cyclic changes in tilt of axis
• Precession cyclic change inwobble of the axis
• Variations affect amount and distribution of
  solar energy received by Earth
• Influence climate