Greenhouse Climate September 11, 2014

Earth 100 Mya -Global sea level 100m higher than today -No permanent ice -Middle Cretaceous -Dinosaurs, turtles, and crocodiles living north of Arctic Circle

Mid-Cretaceous Temperature Estimates vs Modern Temperatures

-Ocean Heat Transport Hypothesis – During the Cretaceous, the oceans were carrying twice as much heat from the tropics to the poles -This would have prevented the tropics from becoming too warm -High ocean salinity caused warm tropical waters to sink contributing to poleward movement of energy -Ocean temperatures confirmed by analyzing oxygen isotopes ratios in plankton shells

-Not a linear relationship between temperature and CO 2 levels -This caused by positive feedback effects from snow and sea ice -Icehouse worlds respond quickly to changes in CO 2 -Small CO 2 increases greatly reduce the extent of bright reflective areas, while decreases enlarge it -Greenhouse world much less sensitive to changes in CO 2 -CO 2 saturation – the atmosphere can only hold so much CO 2

Causes of Tectonic-Scale Changes in Sea Level 1- Changes in the volume of ocean ridges: The expansion of ocean crust causes water to displaced upward

2- Collision of Continents: continental collisions reduce the original area of continents and increase the area of ocean basins

3- Water stored in ice sheets: sea level falls when ice sheets are present on the land and rises when they melt

4- Thermal contraction of water: ocean water has the capacity to expand and contract with temperature changes

KT Boundary Layer

Greenhouse world 55mya