CO 2 and Long-Term Climate

1. Chapter 4 CO2 and Long-Term Climate 彭于珈

2. Greenhouse Worlds • Compare with Venus • Venus is a hot planet • Distance0.72 AU • Surface temperature4600C • Consider albedo

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

4. The Venus higher albedo reduces the amount reaching its surface to just over half that of Earth • Consider albedo • The CO2 in the atmosphere • Venus = 96 % • Earth = 0.02 % • Greenhouse effect • Venus2850C4600C • Earth310C150C

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%

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

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

12. Carbon Exchanges • Between Rocks and Atmosphere • Volcanicinput of carbon from rocks to the atmosphere • Removal of CO2 from the atmosphere by Chemical Weathering

13. 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?

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 • CO2  derived from the atmosphere Removal from the Atmosphere Silicate rock (continents) Carbonic acid (soil) Shells of organisms

18. Dissolution • The rate is faster than hydrolysis Removal from the Atmosphere Limestone (rock) In soils Shells of organisms Returned to atmosphere

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 CO2 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 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

25. Another Greenhouse Gas • CH4 & NH3 • Also warmed the early Earth • But such contribution is smaller than CO2 • 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 CO2 cycle • The action of land plantsCO2H2CO3 • The shell-bearing ocean plankton CO2CaCO3

27. 430 Myr 2.1 Byr 2.3 Byr 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. 2.5 Byr 3.5 Byr

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