11/2/2011
175 Million Years Ago
Greenhouse Climate
100 Million Years Ago
• Mid Cretaceous Period
• Most Present-day Continents Separated
from each other
• No Glaciation
• Sea Level 200 m higher than today
• Large continental areas inundated by sea
Mid Cretaceous Period
100 Million Years Ago
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Jurassic Period
Pangea breaking apart
Dinosaur’s heyday
First Birds and small Mammals
Scotland 63 - 73 oF (now 45 - 55 oF)
We know it was Warm
100 Million Years Ago
• Fossils from Warm adapted animals
(dinosaurs & crocodiles) North of Arctic
Circle and South of Antarctic Circle
• Fossils of Warm adapted Vegetation (broad
leafed evergreen trees (breadfruit) much
farther North and South than now
• Coral Reefs much farther from Equator than
today
Temperatures by Latitude
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Dependence of Temperature on
Carbon Dioxide
Slow Rise of Temperature at
High levels of Carbon Dioxide
• Lack of snow and ice to provide positive
feedback
• Saturation - Adding more carbon dioxide
does not cause much more absorption
Why Sea Level Changes
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Sea floor spreading rate changes volume
Continents Colliding
Volcanic Plateaus
Storage of sea water in Ice Sheets
Thermal Expansion of water when heated
Fast
Volume of
Oceans
change as Sea
Floor
Spreading
Rate Changes
Subsidence of Ocean Ridges with
time as they cool
(Hot crust expands upward)
Different Sea Floor Spreading
Rates at the Present Time
Resulting in 200-300 m drop since Cretaceous
Slow
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When Continents Collide
The Land Area is Decreased
Volcanic Plateaus Underwater
Displace Water
Resulting in 10-40 m drop since Cretaceous
Resulting in 40 m drop since Cretaceous
Water
Stored in
Ice Sheets
Resulting in 72 m
drop since
Cretaceous
Thermal Expansion
• When water warms it expands
• When water cools it contracts
• Resulting in 7 m drop since Cretaceous
Sea Level Adjustment
• Adding more water to area of ocean adds
weight
• Extra weight pushed down ocean floor
• This cancels ocean rise by up to 30%,
especially for adding water from glaciers
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11/2/2011
Effects of Sea Level Change on
Climate
Climate Effects of
Asteroid Impact
• More maritime areas so more maritime
climate (milder winters and cooler
summers)
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