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Chapter 4. CO 2 and Long-Term Climate. 彭于珈. Greenhouse Worlds. Compare with Venus Venus is a hot planet Distance0.72 AU Surface temperature 460 0 C Consider albedo. albedo 80 % receive20 %. albedo 26 % receive74 %. The Venus higher albedo reduces the amount reaching - PowerPoint PPT Presentation
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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