Lecture 17Lecture 17

Tectonic-scale Climate ChangeText book: Ch. 4, p64-67, 71-80, 82-86.

• Four Main Processes:– Land-ocean spatial configuration: control where ice sheets form

– Spread of sea floor: volcanoes and oxidation of organic carbon in sedimentary rocks, control release of CO2 in the atmosphere

– Chemical weathering: control CO2 removal process, a thermostat of the earth’s climate

– Uplift-mountain effect: expose fragmented and fresh rock for chemical weathering

How does tectonics influence climate?How does tectonics influence climate?

Plate tectonics and drift Plate tectonics and drift concentratedconcentrated continents at continents at higher latitudeshigher latitudes allowed for allowed for more ice covermore ice cover, which reflected more sunlight and , which reflected more sunlight and created a positive feedback to cause created a positive feedback to cause greater coolinggreater cooling..

Hundreds of millions of yearsHundreds of millions of years

Earth’s climate history:

• Early Earth’s history (4.5BY-570MY):

– 3.7 BY: May have been 10C warmer

– 2.7-1.8BY: widespread glaciers, “snowball earth”

– 1.8-1 BY: warm and ice-free, maybe due to catastrophic events, e.g., volcanoes, cometary impact, overturn stagnant ocean

– 850-590MY: at least two ice ages

580-0MY: 580-225MY: climate changes was generally colder than the period of 225-

65MY. 225-65MY: climate was generally warmer with perhaps the warmest during

mid-Cretaceous (100MY).65-0MY: Earth’s climate became colder with time.

Why?

Mass extinctions of species

Snowball earth

warmest

coldest

In-Class Question: Can you link the tectonic movement to the following climate change?

580-225MY: climate changes was generally colder than the period of 225-65MY. 225-65MY: climate was generally warmer with perhaps the warmest during mid-Cretaceous (100MY).65-0MY: Earth’s climate became colder with time.

Seafloor spreading leads to increased Seafloor spreading leads to increased periods of periods of volcanic degassing of COvolcanic degassing of CO22, ,

which causes warming.which causes warming.

Higher temperaturesHigher temperatures leads to leads to increased increased weatheringweathering, which will , which will remove COremove CO22

from the atmosphere and reverse from the atmosphere and reverse warming in warming in a negative feedback loopa negative feedback loop..

Tectonic-scale Carbon Dioxide Fluctuations Tectonic-scale Carbon Dioxide Fluctuations (p. 71-75)(p. 71-75)

Earth’s Climate History in the Last 550 Myr1. Over the past 550

Myr, three Icehouse periods (430, 325-240, 35-0 Myr ago).

2. For most of the last 550 Myr or the earth’s entire history, the climate was much warmer than today.

3. Tectonic-scale climate change is caused byplate tectonics

Land/ocean positions and sizesOcean floor spreading/CO2 increase Mountain building (uplift) &

weathering / CO2 decrease

Part II p. 82-83; Ch. 4, 5, 6, 7

4. Other causes.

Chemical weathering (chemical breakdown of minerals or rocks)-a thermostat of earth’s climate (Ch. 4, p75-80)

Carbonic acid

Examples: (Calcite) (calcium ions)Limestone + carbon dioxide + water dissolved ions + bicarbonateCaCO3 + CO2 + H2O Ca2+ + 2HCO3

-

Cretaceous Greenhouse Earth

Warm period of dinosaurs

Evidence

No record of glaciers or polar ice capsFaunal/floral zone latitudinal shiftIsotopes warmer oceansEnvironments shift with near tropics to the poles

Oceans/Atmosphere/Land Features

Sea level 100-200 m higher because of no polar ice capsIntense storms (hurricanes) because of warmer watersStronger hydrologic cycleLess wind because lower T and P gradients globallyMore plants, more flowers; extent of dry land reduced by flooding

Causes

Sun-Earth relationshipLand-sea configuration

More oceans in low latitudeslower albedoMore land in high latitudesmore plants

More CO2 in atmosphere (4-8 x)

The World 100 Myr Ago (p. 82-85)The World 100 Myr Ago (p. 82-85)

Flooding of The Flooding of The ContinentsContinents

100,000 years

18,000 years

230,000 years

1 Million years

3.5 Million years

10 million years6 5 million years

10,000 years

1,000 years

55 million years

PR

ES

EN

T1. The last time atmospheric CO2 concentrations and temperatures were much higher than today was in the age of dinosaurs.2. Agriculture revolution began 10,000 years ago.3. Human population explosion in the past 100 years. Today: 6 billion

Sea levels were much higher than today, and Texas was mostly under water

What about Texas?

Climate change was one important reason that the dinosaurs disappeared.

Causes: decrease in ocean floor spreading rate; uplift weathering; ocean heat transport through gateways; ice-albedo feedbacks

Ch. 7

Cooling from leaf outline Cooling from ocean isotopes

Decrease in spreading rate

Global Cooling Trend in the Last 55 Myr

Summary:

• Four Main Processes control the link between tectonic movement and climate:– Land-ocean spatial configuration: control where ice sheets form

– Spread of sea floor: volcanoes and oxidation of organic carbon in sedimentary rocks, control release of CO2 in the atmosphere

– Chemical weathering: control CO2 removal process, a thermostat of the earth’s climate

– Uplift-mountain effect: expose fragmented and fresh rock for chemical weathering