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:
Consider albedo The CO 2 in the atmosphere Venus = 96 % Earth = 0.02 % Greenhouse effect Venus 285 0 C 460 0 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
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%
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
Carbon Exchanges between Rocks and the Atmosphere
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
Volcanic Input When volcanic eruptions and the activity of hot springs rate 0.15 x 10 15 grams/year But how could balance at the long intervals of geologic time?
Oxidation of organic carbon in sedimentary rocks
Chemical Weathering Hydrolysis Main mechanism Dissolution
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
Dissolution The rate is faster than hydrolysis Limestone (rock) In soilsShells of organisms Removal from the Atmosphere Returned to atmospher e
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 CO 2 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 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
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
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
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
Primitive single-celled marine algae 3.5 Byr ago