COCO22 and Long-Term and Long-Term ClimateClimate

COCO22 and Long-Term and Long-Term ClimateClimate

彭于珈彭于珈

Chapter 4

Greenhouse Worlds

• Compare with Venus• Venus is a hot planet

Distance0.72 AU

Surface temperature4600CConsider albedo

93.1518.0

1

72.0

12

2

Venus

Earth

kmAU 8105.11

albedo26 %receive74 %

albedo80 %receive20 %

Consider albedo

The CO2 in the atmosphere

Venus = 96 %Earth = 0.02 %

Greenhouse effectVenus2850C4600CEarth310C150C

52.074.0

20.093.1

The Venus higher albedo reduces the amount reaching its surface to just over half that of Earth

The Faint Young Sun Paradox

• Nuclear reactionfuses nuclei of H together to form Hecaused Sun to expand and brighterThe models indicate that the earliest

Sun shone 25% to 30%

Completely frozen Earth?

• In astronomy Yes• In climate No• Some evidences indicate that

Earth was not frozen solid anytime

• Something must have kept the early Earth warm enough to offset the Sun’s weakness

Thermostat (temperature regulator)

• Recall the temperature on Venus• Where is the carbon reservoir?

Venus atmosphereEarth rocks

Carbon Exchanges between Rocks and the

Atmosphere

Carbon Exchanges

• Between Rocks and Atmosphere• Volcanic input of carbon from

rocks to the atmosphere

• Removal of CO2 from the atmosphere by Chemical Weathering

Volcanic Input• When volcanic eruptions and the

activity of hot springs• rate 0.15 x 1015 grams/year• But how could balance at the long

intervals of geologic time?

yearsreservoirsdeep

yearsreservoirssurface

yearsatmosphere

000,27815.0

41700_

700,2415.0

3700_

400015.0

600

Oxidation of organic carbon in sedimentary rocks

22 COOC

Chemical Weathering

• HydrolysisMain mechanism

• Dissolution

Hydrolysis

• Three key ingredientsMinerals silicate mineralsWater derived from rainCO2 derived from the atmosphere

22 COO　H

OHSiOCaCOCOHCaSiO 223323 Silicate rock(continents)

Carbonic acid(soil)

Shells of organisms

Removal from the

Atmosphere

Dissolution

• The rate is faster than hydrolysis

22 COO　H

223323 COOHCaCOCOHCaCO Limestone

(rock)In soils Shells of

organisms

Removal from the

Atmosphere

Returned toatmosphere

Control Factors

• Temperature• Precipitation• Vegetation• They are all mutually reinforcing

to affect chemical weathering

Climate Factors that control Chemical

Weathering

Scientists estimate that the presence of vegetation on land can increase the rate of chemical weathering by a factor of 2~10 over the rate on land that lacks vegetation.

Chemical Weathering :Earth’s Thermostat ?

• The average global rate of chemical weathering depends on the state of Earth’s climate.

• But weathering also has the capacity to alter that state by regulating the rate at which CO2 is removed from the atmosphere.

• The weathering thermostat works as a negative feedback

• Negative feedback simply moderate the degree of climate change

Faint young Sun paradoxEarth was not frozen solid

• The volcanism was much higher early in Earth’s history

• Slower rates of weathering would have left more CO2 in the atmosphere

• As Earth began to receive more solar radiation from the brightening Sun

Another Greenhouse Gas

• CH4 & NH3

Also warmed the early EarthBut such contribution is smaller than CO2

• water vaporThe most important greenhouse gas

todayIt acts as a positive feedback that

amplifies changes in climate

Is life the Ultimate Control on Earth’s Thermostat?

The Gaia Hypothesis • The biologists James Lovelock and

Lynn Margulis proposed in the 1980s that life itself has been responsible for regulating Earth’s climate.

• Chemical weathering thermostatCarbon is at the center of the CO2 cycleThe action of land plantsCO2H2CO3

The shell-bearing ocean planktonCO2CaCO3

FIGURE 4-9 The Gaia hypothesisOver time, life-forms gradually developed in complexity and played a progressively greater role in chemical Weathering and its control of Earth’s climate. The Gaia hypothesis holds that life evolved in order to regulate Earth’s Climate.

3.5 Byr

2.5 Byr

2.3 Byr

2.1 Byr

430 Myr

Primitive single-celled marine algae

3.5 Byr ago

First primitive land plants

430 Myr ago

The first treelike plants

400 Myr ago