1. CO2 and Long-Term Climate
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
接收輻射量與距離成反比，金星是地球的1.93倍
雖然很高，可是也不全是這個關係，也要考慮其它因素。如反射率和co2含量。

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

4. The CO2 in the atmosphere
Consider albedo
The CO2 in the atmosphere
Venus = 96 %
Earth = 0.02 %
Greenhouse effect
Venus2850C4600C
Earth310C150C
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%
核融合的過程，使太陽越長越大。
以前太陽比現在小25~30 %

7. Completely frozen Earth?
In astronomy  Yes
In climate  No
Some evidences indicate that Earth was not frozen solid anytime
天文上說地球曾經很冷過。
但氣象卻否
Why ?

9. Thermostat (temperature regulator) Recall the temperature on Venus
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
回想前面金星與地球，金星因為co2很多，所以很熱。
地球的carbon在rock中
金星的carbon在atmosphere中

10. Carbon Exchanges between Rocks and the Atmosphere

12. Carbon Exchanges Between Rocks and Atmosphere
Volcanic input of carbon from rocks to the atmosphere
Removal of CO2 from the atmosphere by Chemical Weathering
天文上說地球曾經很冷過。
但氣象卻否

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?
有機碳在rock中氧化，最後以co2形式釋出到大氣裡。

14. Oxidation of organic carbon in sedimentary rocks

15. Chemical Weathering Hydrolysis Dissolution Main mechanism 天文上說地球曾經很冷過。
但氣象卻否

16. Removal from the Atmosphere
Hydrolysis
Three key ingredients
Minerals  silicate minerals
Water  derived from rain
CO2  derived from the atmosphere
Removal from the Atmosphere
天文上說地球曾經很冷過。
但氣象卻否
Silicate rock
(continents)
Carbonic acid
(soil)
Shells of organisms

18. Removal from the Atmosphere
Dissolution
The rate is faster than hydrolysis
Removal from the Atmosphere
Limestone
(rock)
In soils
Shells of
organisms
Returned to
atmosphere
天文上說地球曾經很冷過。
但氣象卻否

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.
全球平均風化速率視地球氣候型態而定。
但風化也會影響大氣中co2的移除。

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 CO2 in the atmosphere
As Earth began to receive more solar radiation from the brightening Sun
現在可以解釋為何地球不會完全冰凍

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
講完之後就講：是否還有其它原因可以控制這個thermostat
如生活。生物圈，蓋亞假說。

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 2.5 Byr 3.5 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.
35億年前：單細胞生物出現
25億年前：細胞核
23億年前：大氣中出現O2
21億年前：多細胞生物
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