Weekly Progress and Study Guide by Chapter

Content

1. Fundamentals  (1 week)
    Overview
    Historical background
    The natural carbon cycle
    The anthropogenically altered carbon cycle

Overview (Slide Set 1):
Key slides: Slide #11 (The disturbed carbon cycle), carbon pools and fluxes, units to measure them
CO2 has changed from 280 to 390ppm since industrial time (39%)
Greenhouse effect: Earth vs Venus and Mars
Basic units: ppm, GtC, PgC, GtC/y ...
Carbon footprint: 1 tC/person global average
The disturbed Carbon cycle diagram (pools and fluxes)   

2. Climate basics (2 weeks)
    Fundamental controls of Earth's climate: energy balance
    Greenhouse effect
    One-layer atmosphere model
    General circulation of the atmosphere: Global patterns of wind, pressure, precipitation and temperature
    Hadley and Walker Circulation, mid-latitude storms
    Short-term climate variability: ENSO, NAO, monsoons  
    Climate sensitivity and climate feedbacks
    Climate projection
    Impact and vulnerabilities

Review Guide

Why CO2 and H2O are greenhouse gases but O2 and N2 are not? Absorption bands and windows
Climate sensitivity and climate feedbacks
Stefan-Boltzman Law: F=σT4, with which we can derive climate sensitivity in the absence of feedbacks
Energy balance and atmospheric general circulation:
Climatology (precipitation and wind/pressure patterns) and vegetation/carbon distribution

Slide sets:

 "Eneargy balance and general circulation"
"Climate change and variability"
Handout: chpater on "climate variability and climate change"


3. Processes underlying the natural carbon cycle (2 weeks)
    Ocean
    Land 
    Atmosphere
    Seasonal cycles

Review Guide:
Residence time in the main carbon pools (caution: diagnostic only, may representing very different processes)
Carbon budget of anthropogenic CO2: the 'missing' carbon sink
Be careful about the distinction/relation between pool and flux (or stock and flow):
dC/dt = Fin-Fout = Fnet.
Example: Over a seasonal cycle, CO2 concentration (pool size) lags NH vegetation growth (flux)
Ocean: solubility, biological and carbonate pumps
Henry's law
Pure rainwater pH=5.6, but pH of seawater is about 8
Carbonate chemistry: CO2 reacts with water, leading to bicarbonate and carbonate formation. Ratio of H2CO3*:HCO3-:CO32- is roughly 1:100:10 (a more precise number is ?). As a result, the ocean stores 100 times more carbon than would if CO2 did not react with water (solubility defined by Henry's Law only). Also, for fossil fuel carbon emitted into the atmosphere, about 10% (CO2/CO32-) of CO2 will remain in the atmosphere (related to the Revelle factor).
Terminology: DIC (=H2CO3*+HCO3-+CO32-), DOC
Biological pump: moves CO2 from surface to deep ocean. Without it, CO2 would be about 150 ppm higher.
Carbonate pump
Carbonate (limestone) dissolution/sedimentation keeps ocean pH in check. The Ca2+ cation is a main base to neutralize the acidity from CO2, therefore the large C reservoir in the ocean. But this is a slow process.
Marine snow
Carbonate compensation depth
Geological
The balance between weathering/sedimentation/burial and volcanic release controls long-term carbon cycle; their imblance is key for long-term CO2 variations
Weathering of limestone (CaCO3) does not sequester carbon, but the weathering of silicate (e.g., CaSiO3) does.
Organic vs inorganic: fossil fuel is derived from ancient organic matter; burial of organic carbon is a long-term carbon sink, while responsible for much of the atmospheric O2.
Terrestrial
C3 vs C4
Terminology: GPP, NPP, Re, Rh, NEP
Multiple turnover time in of soil carbon pools
Trophic level
Global NPP = 60 GtC/y, corresponding to land average 0.5 kgC/m2/y
Environmental controls on photosynthesis and decomposition:
dC/dt = photosynthesis(light, moisture, temperature, CO2) -respiration (temperature, moisture)

4. Variability of the carbon cycle (1 week)
    The Mauna Loa CO2 record: many tales it tells
    ENSO, drought, disturbances such as fire
    other modes of variability
    Recent warming induced changes, espeicially in the arctic region

Review Guide

Variability on multiple timescales:

Anthropogenic: 280-380 ppm (and rising)

Holocence (last 10,000 years): 280±10 ppm

Pleistocene glacial interglacial cycles (last 1My): 190-280

Phanerozoic (last 500 My): 1-10 PAL (present Atmo CO2 level)

Mauna Loa CO2 as a ‘catch-all’ indicator of the carbon cycle and climate; many tales it tells:

CO2 concentration vs CO2 growth rate (dCO2/dt): pool vs flux

dCO2/dt = FFE + Foa + Fta where Fta=Rh-NPP

(1) Seasonal cycle dominated by the balance of Northern Hemisphere terrestrial photosynthesis uptake (draw down atmospheric CO2) and decomposition (increase atmospheric CO2). CO2 max in May and min in Sep-Oct (end of NH growing season).

Seasonal cycle amplitude has changed over time: causes unresolved but hypothesized high-latitude warming, and midlatitude drought

(2) Interannual variability

CO2 growth rate (dCO2/dt) correlates with ENSO, mostly due to terrestrial biosphere response to especially tropical drought (a ‘conspiracy’ between ENSO climate anomaly and plant/soil physiology). Ocean flux is in the opposite direction

Roles of fire, volcanic eruption, etc.

(3) Methods to diagnose/understand CO2 variability

Mechanistic models

Atmospheric CO2 inversion

CH2O+O2=CO2+H2O:  fossil fuel burning causes not only CO2 to increase, but also O2 to decrease

Isotopes of C (C13: indicator of biological activity; C14: indicator of old carbon such as fossil fuel)


5. Carbon cycle change on geological timescales (1-2 weeks)
    The faint young Sun paradox
    Last 500 million years
    Glacial-interglacial cycles
    Holocene

Review Guide

Variability on multiple timescales:

Anthropogenic: 280-380 ppm (and rising)

Holocence (last 10,000 years): 280±10 ppm

Pleistocene glacial interglacial cycles (last 1My): 190-280

Phanerozoic (last 500 My): 1-10 PAL (present Atmo CO2 level)

CO2 has changed on geological timescales.
    CO2 often (but not always) co-varies with climate
        Early Earth:  probably many times higher than today
        Major glaciations, possibly nearly completely snow-covered Earth (Snowball Earth), closely linked to CO2
        Mesozoic (Dinosaur's time): CO2 at least 10 times higher than today, and climate was warming (no permanent ice on Earth)
    We are in an ice age now (since the extinction of dinosaurs)
    During Pleistocene (last 2 million years), Earth has been experienceing increasing oscillations of glacial-interglacial cycles.
        Dominanted by 100ky cycles over which global temperature changes by 5C, and CO2 from 180ppm to 280ppm, sea-levels changes by 120m
            At the last glacial maximum (LGM) 21 ky ago, many parts of Northern Hemisphere land were covered by icesheets
            The Laurentide Ice Sheets covered the whole Canada, all the way to New York.
            Orbital change may be important driver, but the mystery is still unresolved.
    Holocene (last 10,000 years) has relatively stable climate and CO2
            The early Anthropocene hypothesis: Did agriculture release enough CO2 to reverse the trend of glaciation?
   


6. Sources and sinks of anthropogenic carbon (2 weeks)
6.1 Fossil fuel emissions
        Origin of coal, oil, gas; van Kevelen Diagram: transformation of biomass to fossil fuel
        Fossil fuel and energy use; Energy vs carbon content
        Energy Consumption, economics and CO2 emissions      
6.2   Land use, land cover, land management: deforestation, etc.
6.3   Carbon sinks: Closing the carbon budget
    The 'missing' carbon sink on land
    Sinks in the ocean and a lot more
    Closing the carbon budget

6.1 Fossil fuel emissions
        Origin of coal, oil, gas; van Kevelen Diagram: transformation of biomass to fossil fuel
        Carbon/Energy content (C:E ratio) indicates CO2 released for a unit amount of energy contained in the fuel.
            Approximately, the relative raitos of C:E ratio for major fuels:
                    Wood : Coal : Oil : Gas = 6 : 5 : 4 : 3
                    Example: Replace coal with gas emits 40% less CO2 for the same amount of energy generated
        Estimate CO2 emissions from fossil fuel use: 
            Production: how much coal, oil, gas is produced by country, plus international aviation/shipping, cement production/gas flare; then convert to CO2 with "emission factors"
            Consmption: basically carbon footprint calculation for all kinds of activities       

6.2/6.3 Closing the carbon budget

Atmospheric view: dCO2/dt = FFE + Foa + Fta where Fta=Rh-NPP

Sink view: FFE = dCO2/dt + Fao + Fat(net)

1990-2000 6.4 3.1 2.2 1.0 (=2.6 residual - 1.6 Landuse)

2000-2009 7.7 4.1 2.3 1.3 (=2.4 residual – 1.1 Landuse) GtC/y

Uncertainty in land use: Fat(residual/missing sink) = Flu+Fat(net)=1.1+1.3=2.4 (GCP 2010)

Airborne fraction of FFE CO2: AF=4.1/7.7=53%

Airborne fraction of FFE+Landuse: AF_lu = 4.1/(7.7+1.1) = 47%

AF increased slightly over the last 50 years: saturation of carbon sinks?

Possible reasons of the ‘missing’ (residual) land carbon sink: still unresolved

Mostly in the Northern Hemisphere

CO2 fertilization, nitrogen deposition

Forest regrowth, wood product, no till agriculture, woody encroachment, sedimentation, …

Uncertainties in  dCO2/dt (1-2%),  Foa (<5%), FFE (10%),  Fta (100%), FLU (100%)



       

7. What's happening to the carbon cycle now and future projections (1 week)
    Recent changes
    Projections
    Integrated assessment
    Carbon-climate feedbacks

    The long-life time of CO2

8. Carbon management, energy use and options for the future (1 week)
      Rnewable energy resources
      Carbon sequestration
      Geoengineering