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Module 7 Part II The Carbon Cycle. Carbon on Earth Chapter 8.

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Presentation on theme: "Module 7 Part II The Carbon Cycle. Carbon on Earth Chapter 8."— Presentation transcript:

1 Module 7 Part II The Carbon Cycle

2 Carbon on Earth Chapter 8

3 The Chemistry of Carbon  Biotic carbon  Highly organized molecules within living things  Abiotic carbon  After life they become disorganized goo – called kerogen, or humic acids

4 All three planets had about the same amount of carbon: Venus has the carbon content in it’s very dense atmosphere of carbon dioxide and sulfuric acid Earth has the highest concentration of carbon in limestone and rocks Mars has it’s carbon locked up in the polar ice caps that are carbon dioxide dry ice Terrestrial Planets Venus, Earth, and Mars

5  The backbone of life  A means of storing energy  Photosynthesis, carbon dioxide, water, and sunlight produces plants that store energy as food  The early plants were converted to fossil fuels – more stored energy as fuel instead of food Organic Carbon

6  Methane is totally reduced carbon, has an oxidation state of -4  To calculate oxidation states we assign the common states to hydrogen and oxygen, then realize that the molecule has to be neutral, so the leftover number is assigned to carbon  Hydrogen is +1, there are four of them in methane, so the carbon must be -4  This is fully reduced carbon  Reduced carbon is easily oxidized  CH O 2 → CO H 2 O Oxidation states, electron bookkeeping

7  CO 2 is fully oxidized  The oxidation number for carbon is +4  We calculate this by assigning -2 to each oxygen (Group 16 in the periodic table, needs two more electrons)  Oxygen is -4, so carbon must be +4  Oxidized carbon is stable, low energy, and the preferred state for carbon  Oxidized carbon will not become reduced carbon without a great deal of effort  In between is the carbohydrates, where carbon has a zero oxidation state CH2O formaldehyde, is the simplest carbohydrate. O is -2, H is +1(x2) so C must be in the 0 oxidation state Oxidized carbon

8  Photosynthesis uses oxidized carbon to reduce the carbon to carbohydrates  We use carbohydrates as fuel and oxidize the carbohydrate back to CO 2 when we exhale during respiration Animals are not the only organisms to breathe! Carbon forms

9 The Land Breathes

10  The land inhales CO2 in the summertime growing season and exhales during the winter months  Reversed in the Southern Hemisphere where there is less land  The land breathes on an annual cycle

11 The Ocean Breathes

12  The carbon is inorganic, and stable, it involves the carbonate buffer system that we will study in chapter 10, this is called dissolved inorganic carbon  The ocean effects atmospheric CO2 on time scales of centuries  The glacial-interglacial cycles were amplified somehow by the ocean carbon cycle.

13 The Rocks Breathe

14  The sedimentary rock carbon pool is larger than the ocean, land or atmospheric pools  Carbon in the solid Earth exists as limestone CaCO3, and to a lesser extent, organic carbon  Most of the organic carbon in sedimentary rocks is kerogen  Kerogen is useless as a fossil fuel because it is too diluted  The solid Earth is the largest but slowest breathing of the carbon reservoirs

15 The Atmosphere is the Grand Central Station for the CO 2 Cycles

16 The beat of the ice-age rhythm apparently originates from variation in the Earth’s orbit around the sun The orbit varies through three main cycles, and the orbital variations drive climate by changing the distribution of sunlight at the Earth’s surface  1. Precession Cycle  2. Obliquity Cycle  3. Eccentricity Cycle Glacial-Interglacial Cycles

17  The axis of rotation spins like a wobbly top  Called the precession of season, or the precession of the equinoxes  Completes the entire circle in 20,000 years  Solar heat influx variability comes from precession  Seasonal cycle in the North is weakened and in the South it is intensified because the Earth is closest to the sun in the winter season in the northern hemisphere Precession

18 Precession orbital cycle

19  The angle of the pole of rotation relative to the plane of Earth’s orbit  Varies between 22 and 25.5 degrees  Angle of tilt is currently 23.5 degrees  Cycle time is 41,000 years  The impact of obliquity on solar heating is strongest in the high latitudes Obliquity

20 Obliquity of Earth’s Orbit

21  The third cycle involves how elliptical the orbit of the Earth is  The eccentricity of the orbit has cycles of 100,000 and 400,000 years  At present the orbit of Earth is nearly circular  The orbital cycles affect climate by redistributing the energy from one place to another and from one season to another Eccentricity

22 Milankovitch cycles

23  At the cool surface of the Earth, oxidized carbon wants to be calcium carbonate – limestone  In the hot interior of the Earth, oxidized carbon wants to be free, as CO 2  The CO 2 thermostat regulates atmospheric CO 2 and climate on geologic time scales of hundreds of thousands of years  It is possible to change the set point of the thermostat, creating a hot house world like that of the dinosaurs, or an icy world like today  The thermostats of Venus and Mars are broken The CO 2 Thermostat

24  1. the most stable form of carbon on Earth is oxidized. Photosynthesis stores energy from the sun by producing organic carbon, which is the backbone of life  2. There is less carbon in the atmosphere that any other carbon reservoir. These other reservoirs tug on atmospheric CO 2 seasonally for the land, and on glacial interglacial 100,000 year time scales from the ocean  3. The weathering of igneous rocks on land controls the partial pressure of CO 2 in the atmosphere on million year time scales. The thermostat is broken on Venus because no water, and on Mars because there is no volcanic activity left. Take home points of chapter 8

25 Fossil Fuels and Energy Chapter 9

26 All energy comes from the stars, Mostly from our sun Previous definition: watts = joules/second  terawatts = watts, written TW  1,000,000,000,000 watts Energy

27  Wind(Denmark)  Hydroelectric(2% globally)  Solar  Biomass energy Energy sources

28 Renewable  Geothermal  Solar  Wind  Wood  Waste electric power Non-renewable  Fossil fuels  Radioactive elements

29 “Only a small fraction of the buried organic carbon is in a convenient form for fuel” Fossil Fuels

30  Largest reservoir is coal: it was produced in swamps where the organic material was protected from the atmosphere by water  Freshwater has less sulfur, burns “cleaner”  Saltwater swamps contains sulfur, burns to forms aerosols and produce acid rain as sulfuric acid Traditional fossil fuels

31  Begins as plant material (carbon based) Carbon Peat Coal By a pressure and temperature process that takes millions of years. The oldest coal is the cleanest coal. Coal

32 “Coal is the most abundant fossil fuel, and the future of the Earth’s climate depends mostly on what happens to that coal”

33  Coal fired power plants are established  They produce cheap energy  Would be very expensive to replace with a cleaner fuel source until the necessity arises Coal in power plants

34 “ Oil is probably the most convenient but the least abundant of the fossil fuels, so it is the most expensive.”

35  Organic rich sediments buried 2-5 km  50 – 150 ° C  Temperature and pressure converts some of the organics to oil  Higher temperatures produce natural gas, mostly methane  Only a tiny fraction of the oil and gas produced can be harvested Source of oil

36  Oil fuels the transportation industry  More energy per weight than any battery (so far)  Convenient liquid form as opposed to:  Coal, not used in transportation since the steam engine  Natural gas which must be a pressurized container Oil is the most expensive

37 Traditional:  Oil fields – pumped from under ground or water  largest fields in Saudi Arabia, and in Kuwait Non-traditional:  Oil shales – low grade fuel for power plants, Estonia produces about 70%  Tar sands – requires steam (Canada) Sources

38 We have differing opinions here: The oil industry has been saying forty years for a long time but new sources and initiatives keep adding time. “There is enough oil to keep pumping for decades, but the peak rate of oil extraction could be happening right now.” How long will it last?

39  Coal – solid  Oil – liquid  Natural gas – gas usually in the form of methane CH 4 Natural gas

40 “Methane carries more energy per carbon that the others because methane is the most chemically reduced form of carbon.” Reduced form + oxygen → oxidized form + water Along with a release of energy (the ability to do work). Energy of methane

41 Global sources of Energy in 2001

42  China  India  Brazil  U.S.  France  Denmark  Japan Biggest users of energy Energy consumption per dollar GPD (Gross Domestic Productivity).

43  U.S.  Japan  France  Denmark  Brazil  China  India Energy Consumption per person

44  U.S.petroleum, gas, coal  Japanpetroleum, gas, coal  France petroleum, gas, coal  Denmark petroleum, gas, coal  Brazilpetroleum, gas, coal  Chinacoal, petroleum, gas  Indiacoal, petroleum, gas Source?

45 China and India are building new coal fired plants at an alarming rate. New coal plants

46 “Coal is the form of fossil fuel with the potential of increasing the temperature past the turning point of 2° C. The future of the earth depends most on what happens to that coal.” Bottom Line

47  Ultimately, the energy available to humankind includes instantaneous solar energy, which is abundant but spread out; stored solar energy is in the form of fossil fuels; and stored solar energy from stellar explosions in the form of radioactive elements.  Of the fossil fuels, coal is the most abundant. Oil may run out in the coming decades, and the peak rate of oil extraction may be upon us even now. Take home points, Chapter 9

48  We can project energy demand in the future as the product of population, economic growth, and energy efficiency. continued….

49 The Perturbed Carbon Cycle Chapter 10 The atmosphere ain’t what it used to be!

50  Three oxygen atoms  Very reactive  O2 bonds break with UV-c, forming O free radical, recombines with an O2 to form O3  Stratospheric O3 absorbs (filters) UV-b radiation, forming O2 Ozone

51  Phased out production and release of chlorofluorocarbons because it breaks down stratospheric ozone (Freon, aerosol propellants, refrigerants)  Asthma and allergy suffers feel it, plant leaves get burned and scarred Montreal Protocol 1987

52  Is a Good thing  CO2 in the stratosphere sheds heat as IR to space  The ozone depletion causes cooling in the stratosphere  Result: the stratosphere is cooling Stratospheric Ozone

53 Tropospheric ozone comes from several sources. Biomass burning and industrial activity produce carbon monoxide (CO) and volatile organic compounds (VOCs) which are oxidized to form ozone. Nitrogen oxides (NO x ) from industrial processes, biomass burning, automobile exhaust and lightning also form tropospheric ozone. A small amount of tropospheric ozone also comes from the stratospheric ozone layer. /TroposphericOzone_HiRes.jpg Surface/tropospheric Ozone

54 Ozone

55  Ozone hole located over Antarctica is a different problem than the ozone as a greenhouse gas  HNO3 acid clouds react with chlorine, which in turn, consumes the ozone  Satellite was programmed to throw out data that violated common sense, so the hole was a surprise  Revisiting discarded satellite data revealed that the hole had been growing for some time Ozone Hole

56 Methane Natural Sources  Wetland degradation  Termites  Organic carbon in freshwater swamps Human Sources  Energy emissions  Landfills – “swamp gas”  Ruminant animals  Rice agriculture  Biomass burning

57   Overall human impact has doubled since pre-human levels  CH4 is responsible for 25% of anthropogenic greenhouse heat trapping Methane Clathrates – Fire Ice

58  Methane is transient, but CO2 accumulates  Background levels were around 280 ppm until ~ 1750, coinciding with the New World, “pioneer effect”  Deforestation for agriculture and development is one source of atmospheric CO2  The second source is fossil fuel combustion Carbon Dioxide

59 CO2 and CH4, 1000 years

60  CO2 is complicated, and the atmosphere is the exchange place for the three remaining carbon reservoirs  Land cycles annually  Oceans cycle by centuries or more  Rock cycles by millennia or more Atmospheric CO2

61  Deforestation releases about 1.5 Gtons C /year  Fossil fuels release about 8.5 Gtons C /year  Release is about 10 Gtons C /year  Atmospheric levels are rising by about 4 Gtons C /year  Mathematically we are missing about 6 Gtons C /year  There is a missing carbon sink – about 6 Gtons /year The Missing Sink

62  The measurements are variable  The research indicates that the land is taking up the missing carbon  Studies conclude that the “missing sink” is located in the high latitudes of the northern hemisphere Terrestrial Carbon Sink

63  Higher concentrations of CO2 encourages plants to grow faster (greenhouses)  The growth is an initial spurt, and tends to level off  Higher CO2 concentrations fro plants means less water loss when plants open the stomata to take in the CO2 CO2 Fertilization

64  As organic carbon is oxidized to CO2, the soil releases the CO2  Warmer soils decompose faster  Tropical soils contain very little carbon  The permafrost is full of carbon  As soils warm, the CO2 emissions get higher Respiration in Soils

65  Ultimately the fossil fuel CO2 will be cleaned up by the oceans  60 years ago, scientists thought it would be a quick process  50x more CO2 in the ocean  70% of the Earths surface, average 4 km deep Ocean uptake CO2

66  The surface of the ocean limits the contact between the atmosphere and the deep ocean  The ocean uptake of fossil fuel carbon depends on circulation  Ocean ventilation – at high latitudes the cold water sinks and takes gases with it – it takes centuries to make the loop But…

67  The thermocline is a few hundred meters deep, and the ventilation to the atmosphere is a few decades  The surface ocean mixed layer (driven by the wind) is about 100 meters deep and ventilation to the atmosphere is annually Also…

68  In seawater, freshwater lakes, rivers, reservoirs, swimming pools and human blood  The major ions in seawater are Na +, Mg 2+, Ca 2+, K +, Sr 2+, Cl -, SO 4 2- (sulfate), HCO 3 - (bicarbonate), Br -, B(OH) 3 (boric acid), and F -. Together, they account for almost all of the salt in seawater. Buffer chemistry of inorganic carbon

69  Atmospheric CO 2 dissolves in seawater and is hydrated to form carbonic acid, H 2 CO 3. Carbonic acid is diprotic; that is, it can undergo two de-protonation reactions to form bicarbonate (HCO 3 - ), and carbonate (CO 3 2- ). The co- existence of these species in seawater creates a chemical buffer system, regulating the pH and the pCO 2 of the oceans. Most of the inorganic carbon in the ocean exists as bicarbonate (~88%), with the concentrations of carbonate ion and CO 2 comprising about 11% and 1%, respectively. Carbonate/bicarbonate buffer

70  pH reactions, CO2 reacts with H2O to form carbonic acid (carbonated soda drinks) CO2 + H2O  H2CO3  Carbonic acid loses a hydrogen, forms an acidic proton and bicarbonate (hydrogen carbonate) H2CO3  H + + HCO3 -  Hydrogen carbonate loses the second acidic proton and forms more acid and the carbonate ion HCO3 -  H + + Co3 2- What does that mean?

71  We can ignore the tiny input of the Hydrogen ion and recombine the equations to show and easier illustration of le Châtelier’s principal CO2 + CO H2O  2 HCO3 - 1%11%88%  Any additional CO2 is reacted with the carbonate ion to produce the hydrogen carbonate ion Lets Assume

72  A bucket of seawater can absorb or release more CO2 because of the pH chemistry  The buffer stabilizes the pH and the concentrations of the CO2  The amount of CO2 that can be absorbed depends on the concentration of the carbonate  It is about 11% and CO2 is about 1%, so it works well  This buffer system also keeps your blood pH in balance pH Chemistry

73  If you perturb, stress, or change the system, it will react in such a way to relieve the perturbation, stress, or change in the system – it will reach a new equilibrium Perturbation

74  Le Châtelier's Principle states that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change.  In other words, look at the equation, if you add products, it will shift to reactants  If you take away reactants, it will shift to reactants  It will shift to overcome the stress le Châtelier’s Principle

75  The relative concentrations of carbon dioxide and carbonate ion in seawater determine its pH  Fossil fuel CO2 makes seawater more acidic  The buffer helps resist the change in pH  Life forms in the ocean that make their shells out of CaCO3 will suffer at lower pH  Think of putting baking soda (sodium bicarbonate) into vinegar (a weak acid) and watch the CO2 fizz out Seawater pH

76  Eventually after a long period of time, the CO2 will spread out among the carbon reservoirs of the atmosphere, ocean and land surface  Models indicate that the atmospheric levels of CO2 will be higher than before the CO2 was released  Eventually the budget for dissolved CaCO3 in the ocean has to balance  As the buffer chemistry recovers, atmospheric CO2 drops Equilibrium Models

77 The climate cycle will ultimately recover from the fossil fuel era when the carbon returns to the solid Earth as a result of the silicate weathering CO2 thermostat from Chapter 8. Recovery

78 The longevity of the global warming climate event stretches out into time scales of glacial – interglacial cycles, time scales that are longer than the age of human civilization. How long? First we have to stop adding CO2 to the atmosphere.

79  The ozone hole problem is not the same as global warming. They are different issues.  Methane has about a 10 year lifetime in the atmosphere, so its concentration reaches an equilibrium after about this long.  The land surface and the ocean are absorbing some of our fossil fuel CO2, but this could slow or reserve in a changing climate.  Releasing fossil CO2 to the atmosphere will affect climate for hundreds of thousands of years – as far as we are concerned, forever. Take home points, chapter 10


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