New Readings

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