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Greenhouse Earth

鄭琦翰

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outlineExamine the greenhouse world and evaluat

e explanations for its warmth Explore the reasons why sea level 100 Myr

ago was some 200 meters higher than it is today

Evaluate the effects of high sea level on climate

Investigate the climatic and environmental effect of the impact of a giant asteroid that collided with Earth 65 Myr ago

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What explains greenhouse warmth 100 Myr agoAround 175 Myr ago, the giant cont

inent of Pangaea began to break apart

By 100 Myr ago, most of the present-day continents had separated from one another

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Cretaceous

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It is the most recent example in the geologic record of a greenhouse world

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Model simulation of greenhouse world

Model:GCMsData:past distribution of animals and ve

getation,as well as geochemical evidence

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Model:changes in geography(landsea distribution and mountain elevation)

Model:changes in geography and CO2

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The effect of CO2 on climate

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What explains the data-model mismatch

Possible problems with the data

Possible problems with the models

Ocean

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What explains the data-model mismatchOcean(1)ocean heat transport hypothesis(

2)Today,most of the deep ocean receives water from just two polar source areas

(3)The deep ocean 100 Myr ago was filled with warm saline deep water formed in the tropics and subtropics

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A different way of forming deep water

All the deep water that fills the ocean basins today forms in two cold polar regions

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A different way of forming deep water

100Myr ago more of it may have formed in shallow,salty subtropical seas

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What explains the data-model mismatch

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Sea level changes and climate

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We ignore these local effects on sea level and focus on eustatic change—changes that are global scale

Since 80 million years ago, sea level has fallen from this long-tern maximum to its modern position

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Causes of tectonic-scale changes in sea level

Tectonically driven changes in the volume of the ocean basins and their capacity to hold water

changes in volume of ocean ridges collision of continents construction of volcanic plateaus in the ocean

Changes in the volume of water in the ocean as a result of changes in climate

4. water stored in ice sheets

5. thermal contraction of seawater

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1. Changes in volume of ocean ridges

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Ridge depth=2500m+350(crustal age)1/2

(in meters) (at 0 age) (in Myr)

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2. Collision of continents

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3. Construction of volcanic plateaus in the ocean

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4. Water stored in ice sheets:

Today, the Antarctic and Greenland whose ice sheets have extracted a volume of ocean water equivalent to 72 meters of global sea level

5. Thermal contraction of seawater:

The contraction of seawater caused by this cooling has reduced global sea level by roughly 7 meters

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Sea level adjustment

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Effect of sea level change on climate

For large global sea level changes, the synchronous invasion and withdrawal of the sea on many continents should result in simultaneous fluctuations between harsh continental and mild maritime climates in many regions around the world

High sea levels should cause cooler, more maritime summers that favor the persistence of snow and ice through the summer ablation season at very high

latitude, but none occurred

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Asteroid impact

The geologic evidence for this impact includes the worldwide distribution of a thin layer of sediment enriched in iridium(Ir),an element that is rare on Earth but 10000 times more abundant in some kinds of meteorites

Other evidence for an impact event includes small grains of quartz with distinctive textures called “shock lamellae” that are formed by the shock wave of sudden pressures much larger than those found on earth,even in highly explosive volcanoes

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Asteroid impact

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Asteroid impact

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Asteroid impact