The Greenhouse Climate
We Know the Last 100 Myr Pretty Well…
• Why?
• Know– Continental Positon– Shape of the Ocean Basins– Temperature– Sea Levels
Cretaceous: “abundance of chalk”
Pangaea was breaking up….
Sea Level was MUCH Higher….
Climate Evidence
• Warm-adapted vegetation and critters north of the Arctic circle– Brown-leaf evergreens– Turtles and crocodiles
• No continental glaciation• Tropical conditions to 40– Coral growing at the
paleolatitude of New York– NO HARD Freezes in
temperate latitudes.
180 Myr Ago
160 Myr Ago
120 Myr Ago
80 Myr Ago
60 Myr Ago
Why so much warmer?
• Climate models– Geography– CO2 4-6 times current
levels
• Ocean Circulation– Today the atmosphere
transports about double the heat that the oceans transport
– In Cretaceous that ratio was probably reversed
CO2 probably drove the warming
• Note that CO2 effect is not linear
• At low levels snow and ice contribute to positive feedback– They reflect a lot of
solar radiation back to space
• At high levels there is much weaker effects– Little snow to melt– CO2 Saturation
• But water vapor feedback works in the opposite direction
Regression
Transgression
But what causes changes in sea level?
• Changes in Climate– Ice vs no ice….about 50
meters of change in Cretaceous
– Thermal contraction of water ~ 7 meters
• Change in ocean basin volume– Spreading rates (50 to 150
meters)– Continental Collisions (~10
meters)
Fast Spreading
Slow Spreading
Continental Collision• The size of continents
effects the size of oceans (duh….)
• The collision of India with Asia decreased the continental area by 2 million Km2 (and increased the oceans by that amount)– Net effect was about 10
meters of sea level drop
Effects of Sea Level on Climate• Water has a large
heat capacity and moderates regional climates– That’s why
maritime (western ends of continents) climates tend to be milder
• High stands of sea level extend the reach of maritime climates
Climatic Factors
• Ice Sheets– Antarctic ~ 66 meters of sea level rise– Greenland ~ 6 meters
• Thermal Expansion/Contraction– The volume of water changes about 1 part in
7000 per degree C– Given ocean cooling since the cretaceous,
that works out to about 7 meters of sea level drop.
The 55 Myr Spike• We found this spike in
the data…..– Increase in global
temperatures of 5-9 C–Major acidification of
the oceans– Extinction of about half
of the forams• Why?–Major release of
carbon–Methane on the
seafloor
• We found this spike in the data…..– Increase in global
temperatures of 5-9 C–Major acidification of
the oceans– Extinction of about half
of the forams• Why?–Major release of
carbon–Methane on the
seafloor