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 Km 2 (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