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CO 2 and Long-Term Climate 彭于珈 Chapter 4. Greenhouse Worlds Compare with Venus Venus is a hot planet  Distance  0.72 AU  Surface temperature  460.

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Presentation on theme: "CO 2 and Long-Term Climate 彭于珈 Chapter 4. Greenhouse Worlds Compare with Venus Venus is a hot planet  Distance  0.72 AU  Surface temperature  460."— Presentation transcript:

1 CO 2 and Long-Term Climate 彭于珈 Chapter 4

2 Greenhouse Worlds Compare with Venus Venus is a hot planet  Distance  0.72 AU  Surface temperature  C  Consider albedo

3 albedo  26 % receive  74 % albedo  80 % receive  20 %

4  Consider albedo  The CO 2 in the atmosphere  Venus = 96 %  Earth = 0.02 %  Greenhouse effect  Venus  C  C  Earth  31 0 C  15 0 C The Venus higher albedo reduces the amount reaching its surface to just over half that of Earth

5 The Faint Young Sun Paradox Nuclear reaction  fuses nuclei of H together to form He  caused Sun to expand and brighter  The models indicate that the earliest Sun shone 25% to 30%

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7 Completely frozen Earth? In astronomy  Yes In climate  No Some evidences indicate that Earth was not frozen solid anytime

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9 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  atmosphere  Earth  rocks

10 Carbon Exchanges between Rocks and the Atmosphere

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12 Carbon Exchanges Between Rocks and Atmosphere Volcanic input of carbon from rocks to the atmosphere Removal of CO 2 from the atmosphere by Chemical Weathering

13 Volcanic Input When volcanic eruptions and the activity of hot springs rate  0.15 x grams/year But how could balance at the long intervals of geologic time?

14 Oxidation of organic carbon in sedimentary rocks

15 Chemical Weathering Hydrolysis  Main mechanism Dissolution

16 Hydrolysis Three key ingredients  Minerals  silicate minerals  Water  derived from rain  CO 2  derived from the atmosphere Silicate rock (continents) Carbonic acid (soil) Shells of organisms Removal from the Atmosphere

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18 Dissolution The rate is faster than hydrolysis Limestone (rock) In soilsShells of organisms Removal from the Atmosphere Returned to atmospher e

19 Control Factors Temperature Precipitation Vegetation They are all mutually reinforcing to affect chemical weathering

20 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.

21 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 CO 2 is removed from the atmosphere.

22 The weathering thermostat works as a negative feedback Negative feedback simply moderate the degree of climate change

23 Faint young Sun paradox Earth was not frozen solid The volcanism was much higher early in Earth ’ s history Slower rates of weathering would have left more CO 2 in the atmosphere As Earth began to receive more solar radiation from the brightening Sun

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25 Another Greenhouse Gas CH 4 & NH 3  Also warmed the early Earth  But such contribution is smaller than CO 2 water vapor  The most important greenhouse gas today  It acts as a positive feedback that amplifies changes in climate

26 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 thermostat  Carbon is at the center of the CO 2 cycle  The action of land plants  CO 2  H 2 CO 3  The shell-bearing ocean plankton  CO 2  CaCO 3

27 FIGURE 4-9 The Gaia hypothesis Over 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

28 Primitive single-celled marine algae 3.5 Byr ago

29 First primitive land plants 430 Myr ago

30 The first treelike plants 400 Myr ago

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