Transcript Cenozoic Climate Change

Fossils, Paleoclimate
and Global Climate Change
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 (?)
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?
Geologic Record
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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
Indirect Evidence
• Evidence for
– Aridity
– Warm Climate
– Cold Climate
• Recorded by specific types of rocks
Direct Evidence: Ice Cores
• 100,000 years of continuous
record
• Older than 100,000 is too
distorted by plastic flow and
mixing
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
Sediment Cores
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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)
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
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
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
What does the
Geologic 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
Climate History:
20 Ma to Present
• 20 Ma – climate was somewhat moderate
– Similar to present
• 5 Ma – coldest climate of past 65 million
years
Pleistocene Epoch:
the 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
Recent Climate History
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7000-6000 BP - Warm Peak
950-1300’s – Medieval Warm Spell
1300’s – Cool and Wet
1550 – 1850 – “Little Ice Age”
Food For Thought
• How many of the great events of recorded
human history have been directly influenced
by climate?
Recent Climate History
• 7000-6000 BP - Warm Peak – Great Ancient
civilizations (e.g., Mesopotamia, Egypt)
• 950-1300’s – Medieval Warm Spell – Rise of
“modern” European nation-states
• 1300’s – Cool and Wet – Bubonic Plague
• 1550 – 1850 – “Little Ice Age”
– Washington crosses the Delaware
– Winter at Valley Forge
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?
What factors cause changes in
climate?
• Long term vs. short term changes
• Volcanic eruptions
• Earth’s orbital variations
Why did the climate change so
drastically and repeadedly?
• Climate change and variations
in Earth’s orbit
• Eccentricity: elliptical to
nearly circular cycles
• Obliquity: cyclic changes in
tilt of axis
• Precession: cyclic change
in”wobble” of the axis
• Variations affect amount and
distribution of solar energy
received by Earth
• Influence climate