CO 2 and Long-Term Climate

1. CO2 and Long-Term Climate

2. Greenhouse Worlds:Venus and Earth Why is Venus so much warmer than Earth? • Mean temperatures at surface • Venus: 460o C • Earth: 15o C • At first glance, it would seem that distance from the Sun is a major factor

3. Venus is closer to the Sun • Mean distance from the Sun • Venus: 108.2 million km • Earth: 149.6 million km • Venus is 72% (or .72 Astronomical Unit*) of Earth’s mean distance (1.0 A.U.) * An astronomical unit (A.U.) is the average distance between Earth and the Sun and is used for distance measurement in the Solar System.

4. Venus Receives More Insolation • Amount of insolation received varies inversely with the square of its distance from the Sun. • Venus receives nearly twice the solar radiation as Earth does. • But, this isn’t the reason . . . Earth (1)2 1 1.93 = = Venus (0.72)2 0.581

5. Venus • Upper atmosphere • Thick cover of sulfuric acid clouds • High albedo (80%) • Only 20% of insolation reaches the surface.

6. Earth • Clouds reflect 26% of insolation • 74% of insolation reaches Earth’s surface.

7. Less Insolation Reaches the Surface of Venus • Even though receives 1.93 times the insolation the Earth does • The amount reaching its surface is 52% of Earth’s • This is due to the high albedo of the cloud cover on Venus 0.20 0.74 = 0.52 1.93 x

8. The Cause . . .The Thick Atmosphere of Venus • It’s atmosphere is 90 times as dense as that of Earth. • 96% of the atmosphere is carbon dioxide • Venus is said to have a “runaway greenhouse effect.”

9. Venus and Earth • Are Greenhouse planets • Contain nearly equal amounts of carbon • The difference is where they store carbon • Venus: Primarily in its atmosphere • Earth: Most is stored in rocks • Limestones • Also in reservoirs of coal, oil, and natural gas • On Earth the major greenhouse gas is water vapor • Greenhouse heating from atmospheric carbon is relatively small (31o C) • On Venus the major greenhouse gas is CO2 • Enormous net greenhouse warming (285o C) even though atmospheric water vapor is nearly absent

10. The Faint Young Sun Paradox

11. Earth’s Sun • Formed from the solar nebula 4.55 Byr • “Shines” as a result of an ongoing nuclear reaction in its core

12. Fusion in the Sun’s Core • Four hydrogen (H) nuclei (each with a mass of about 4.030 mass units) join to form a helium (He) nucleus with a mass of only about 4.003 energy units. • The mass that seems to be lost is converted to radiant energy • 4 million metric tons of matter are converted into energy every second

13. An Expanding Sun • The earliest Sun had 25% to 30% lower luminosity. • As nuclear fusion caused the Sun to expand, • It became brighter

14. Hertzsprung – Russell (H-R) Diagaram • Shows the relationship of a star’s • mass to its luminosity • The Sun will eventually expand to • a red giant and then end its life as • a white dwarf

15. All Water on the Early Earth Should Have Been Frozen • A decrease in the Sun’s brightness of just a few percent would cause all water on Earth to freeze. • The geologic record shows that Earth has never been completely frozen.

16. Evidence of Liquid Water on Earth Throughout Geologic Time • Sedimentary rocks are a prominent part of the rock record. • Most sedimentary rock indicate a liquid water depositional environment.

17. Evidence of Liquid Water on Earth Throughout Geologic Time 3.2 to 3.5 Bry old Procaryotes from Australia • Primitive life dates back to at least 3.5 Byr ago. • Continued presence of life on Earth along with a succession of increased complexity isn’t congruent with extreme cold. Cambrian marine life

18. Why then, with a weak Sun wasn’t Earth completely frozen for the first 3 billion years of its existence?

19. A Warming Process Must Have Been Present • There must have been a process that warmed Earth. • But, it must not be doing so today • Combined with the strengthening of the Sun Earth would be uninhabitable. • Somehow, Earth has remained within a moderate temperature range during the period of the Sun’s increasing output.

20. A Thermostat Process • A process that : • Warmed Earth when it otherwise would have frozen • Reduced heat upon detecting increasing warmth from the strengthening Sun • Greenhouse Gases could have been part of the mechanism. • More abundant during early Earth history • Decreased as Earth warmed

21. Effect of Greenhouse Gases

22. Carbon Exchange between Rocks and the Atmosphere Over long periods, slow exchanges can produce large cumulative changes in atmospheric CO2

23. Carbon Reservoirs • Largest carbon reservoir is in rocks. • Inverse relationship between size of reservoir and rate of exchange • Over millions of years slow exchanges can result in large changes in atmosphere CO2.

24. Volcanic Sources of CO2 Heat in Earth’s interior causes rocks to melt.

25. Volcanic Eruptions

26. Volcanic Sources of CO2 Heat in Earth’s interior causes rocks to melt.

27. Yellowstone National Park

28. A Balancing Act • Rate of carbon input is roughly balanced by a similar rate of natural removal • Probably prior to industrial revolution • Volcanic input of carbon is irregular because volcanoes don’t erupt on a “schedule.” • If volcanic input of carbon stopped . . . • It would take 4,000 years for atmospheric CO2 to fall to zero. • A geologically short period of time

29. Other Reservoirs Would Compensate • Near surface reservoirs would lose CO2. • Vegetation • Soil • Surface Ocean • They would take 24,700 years after end of volcanism to lose all their carbon. • Deep-Ocean carbon reservoir would also lose. • With this reservoir it would take 278,000 years for a complete termination of volcanic carbon input to completely deplete all reservoirs. • This is 0.01% of all Earth history

30. Is the Volcanic Source of CO2 the Natural Thermostat? • Volcanoes alone could not have delivered the amount of carbon needed to: • Prevent the atmosphere from running out of CO2 • But not overheat the planet • Volcanic processes are driven by Earth’s internal heat. • Volcanism doesn’t react to external changes and then act to moderate their effects like a thermostat.

31. Chemical Weathering of Continental Rocks • The major long-term process of CO2 removal • Avoids long-term buildup of CO2 levels over time • Of the types of chemical weathering previously discussed, two types are important in the carbon cycle. • Hydrolysis • Dissolution

32. Hydrolysis • The main mechanism for removing CO2 from the atmosphere • Three key ingredients • Water derived from precipitation • Minerals in continental rocks • Carbon dioxide from the atmosphere

33. Continental Rocks • On the average, composition of granite • Composed of silicate minerals • Typically cations (Na+, K+, Fe+2, Mg+2, Al+3, and Ca+2 are: • Chemically bonded to the negatively charged silicon-oxygen tetrahedron (SiO4-4)

34. The Silicon-Oxygen Tetrahedron

35. Olivine – A Silicate Mineral

36. Example Using Wollastonite wollastonite • CO2 dissolves in rainwater (and in groundwater) • Forms carbonic acid • Carbonic acid reacts with wollastonite • Weathered products release Si+4, Ca+1, and HCO3-1 • Eventually end up in the ocean and is deposited in shells of marine organisms. • Eventually forms limestone

37. Example Using Wollastonite wollastonite Accounts for 80% of carbon buried per year in sediments and rocks

38. Diatomite • Silica deposited in the deep ocean

39. Limestone • Limestone ridge in the Canadian Rockies • Limestone in France

40. Coral Limestone

41. Barrier Reefs Great Barrier Reef Australia

42. Skeletal Limestone-Coquina • Formed from wave-broken fragments of shells, corals, and algae.

43. Chalk • Fine-grained, light colored, and porous from microscopic marine organisms (plankton).

44. White Cliffs of DoverKent, England

45. Coccolithophorids (Coccoliths) • Primary constituent of chalk in the White Cliffs of Dover • Calcareous platelets • Secreted by yellow-green algae • Extremely small

46. Bioclastic Limestone Coarse-grained with shell and coral fragments Fine-grained carbonate mud from coralline algae

47. Dissolution of Limestone • Rainwater and CO2 combine in soils forming carbonic acid • Calcite in limestone is chemically dissolved • Dissolved ions flow to the ocean in rivers. CaCO3 + H2CO3 Ca + 2HCO3 calcite carbonic acidcalcium bicarbonate

48. Dissolution of Limestone Forming Caves Great Onyx Cave, KY

49. Howe Caverns, NY

50. Carlsbad Caverns, NM