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QUESTIONS

QUESTIONS. How do elements in the lithosphere get transferred to the atmosphere? Imagine an early Earth with a weak Sun and frozen ocean (“snowball Earth”). How would volcanic activity eventually warm the Earth and cause melting of the ocean?

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QUESTIONS

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  1. QUESTIONS • How do elements in the lithosphere get transferred to the atmosphere? • Imagine an early Earth with a weak Sun and frozen ocean (“snowball Earth”). How would volcanic activity eventually warm the Earth and cause melting of the ocean? • Industrial fertilizer (N2+3H22NH3) vs. natural fertilizer (compost): how does each affect the nitrogen cycle?

  2. CARBON DIOXIDE: GEOLOGICAL RECORD Antarctic Ice Core Data CO2 varies over geologic time, within the range 190 – 280 ppm for the last 420,000 years. The variations correlate with climate: cold  low CO2 . Is CO2 driving climate or vice versa? The heavier temperature lines 160,000 BP to present reflect more data points, not necessarily greater variability.

  3. THE CURRENT CO2 OBSERVATION NETWORK

  4. ATMOSPHERIC CO2 INCREASE OVER PAST 1000 YEARS,AND MORE RECENTLY…

  5. 1998-2009 TREND OF CO2 CONCENTRATIONS

  6. GLOBAL FUEL USE 8700 in 2008! Emissions have increased by more than 2X since 1970. But there has not been a corresponding rise in the annual increment of atmospheric CO2. In 1970 ~75% of the emitted CO2 stayed in the atmosphere, but only ~40% in 2000.

  7. RECENT GROWTH IN ATMOSPHERIC CO2 CONCENTRATIONS [IPCC, 2007] The average annual increase did not change much between 1970 and 2000, despite significant increases in fossil fuel emissions. Airborne fraction, CO2 (ppm) 00 02 CO2 Airborne Fraction 1 ppm = 2.1 x 1012 kg of C (in CO2) Average rate of increase per year, 1.5 ppm = 3.25 x 1012 kg/yr—little change (some variations) since 1975.

  8. HOW DOES GROWTH RELATE TO FOSSIL FUEL EMISSIONS? • atmospheric increase is ~50% of fossil fuel emissions • significant interannual variability Arrows indicate El Nino events

  9. GLOBAL PREINDUSTRIAL CARBON CYCLE Inventories in PgC Flows in PgC yr-1

  10. CARBON CYCLE ON LAND • Photosynthesis: • CO2 + H2O + light  "H2CO" + O2 • Respiration: • "H2CO" + O2  CO2 + H2O + energy • Very little organic matter is stored, on average. • Dissolution/evasion • CO2(g) + H2O + CO3(aq) = 2 HCO3¯ CARBON CYCLE IN THE OCEAN

  11. CO2(g) CO2.H2O CO2.H2O HCO3- + H+ ATMOSPHERE UPTAKE OF CO2 BY THE OCEANS KH = 3x10-2 M atm-1 OCEAN K1 = 9x10-7 M Ocean pH pK1 K2 = 7x10-10 M HCO3- CO32- + H+ pK2 CO2.H2O HCO3- CO32- Net uptake: CO2(g) + CO32- H2O 2HCO3--

  12. Equilibrium calculation for Alk = 2.25x10-3 M 100 200 300 400 500 pCO2 , ppm LIMIT ON OCEAN UPTAKE OF CO2:CONSERVATION OF ALKALINITY • The alkalinity is the ability of solution to neutralize an acid (or excess positive charge in the ocean balanced by dissolved C): • Alk = [Na+] + [K+] + 2[Mg2+] + 2[Ca2+] • - [Cl-] – 2[SO42-] – [Br-] • = [HCO3-] + 2[CO32-] • It is conserved upon addition of CO2 • uptake of CO2 is limited by the • existing supply of CO32- • Increasing Alk requires dissolution of sediments: • CaCO3 2.1 2.0 [CO2.H2O]+[HCO3-] +[CO32-], 10-3M 1.9 Often called carbonate alkalinity 1.8 [HCO3-], 10-3M 1.6 1.4 4 [CO32-], 10-4 M 3 2 8.6 Ocean pH Ca2+ + CO32- 8.4 8.2 …which takes place over a time scale of thousands of years

  13. EQUILIBRIUM PARTITIONING OF CO2BETWEEN ATMOSPHERE AND GLOBAL OCEAN Fraction of CO2 in atmosphere (Equilibrium for present-day ocean, pH=8.2): varies roughly as [H+] moles • only 3% of total inorganic carbon is currently in the atmosphere But CO2(g) k [ [H+] k [ F k … positive feedback to increasing CO2 Pose problem differently: how does a CO2additiondN partition between the atmosphere and ocean at equilibrium? varies roughly as [H+]2 [ 28% of added CO2 remains in atmosphere!

  14. FURTHER LIMITATION OF CO2 UPTAKE: SLOW OCEAN TURNOVER (~ 200 years) Uptake by oceanic mixed layer only (VOC= 3.6x1016 m3) would givef = 0.94 (94% of added CO2 remains in atmosphere) Inventories in 1015 m3 water Flows in 1015 m3 yr-1

  15. Observed uptake of fossil fuel CO2 by the oceans compare to ~300 mmoles CO3=

  16. NET UPTAKE OF CO2 BY TERRESTRIAL BIOSPHERE(1.4 Pg C yr-1 in the 1990s; IPCC [2001])is a small residual of large atm-bio exchange • Gross primary production (GPP): GPP = CO2 uptake by photosynthesis = 120 PgC yr-1 • Net primary production (NPP): NPP = GPP – “autotrophic” respiration by green plants = 60 PgC yr-1 • Net ecosystem production (NEP): NEP = NPP – “heterotrophic” respiration by decomposers = 10 PgC yr-1 • Net biome production (NBP) NBP = NEP – fires/erosion/harvesting = 1.4 PgC yr-1 CO2 + H2O  "H2CO" + O2Photosynthesis and Respiration Atmospheric CO2 observations show that the net uptake is at northern midlatitudes

  17. CYCLING OF CARBON WITH TERRESTRIAL BIOSPHERE Inventories in PgC Flows in PgC yr-1 Relatively smallreservoirs a Short time scales a net uptake from reforestation is transitory. ..unless resources are managed to preserve organic matter

  18. GLOBAL CO2 BUDGET [PgC/yr] 1980 – 1990 1990 – 2000 6.5 .5-1 7-7.5 Sources 3.2 1.5-2 1.8-2.8 7-7.5 Sinks

  19. EVIDENCE FOR LAND UPTAKE OF CO2 FROM TRENDS IN O2,1990-2000

  20. MA NH % of land area in forests 20 40 60 80 100 Year 1700 1800 1900 2000 Harvard Forest, Petersham, MA. A "typical" New England forest…an artifact! Fitzjarrald et al., 2001

  21. HUMAN INFLUENCE ON THE CARBON CYCLE Natural fluxes in black; anthropogenic contribution (1990s) in red

  22. EMISSIONS: WHERE ARE WE NOW? 2.8% drop predicted for 2009 based on IMF GDP Update: 1.3% drop in 2009, 3% increase for 2010 [Friedlingstein et al., 2010] [Le Quéré et al., 2009]

  23. SINKS: WHERE ARE WE NOW? MODEL MODEL [Le Quéré et al., 2009] OBSERVATIONS Uncertainties here remain LARGE (1-2 PgC/yr) Accumulation in the atmosphere trending up (ocean and/or land uptake efficiency declining? OR?)

  24. DEFORESTATION OF THE AMAZON SLOWING DOWN… Survey from the Brazilian Ministry of the Environment 47.5% decline! [Science, Sept 10, 2010] Le Quéré et al. [2009] estimate 2008 deforestation (land use) source of 1.2 PgC/yr Total CO2 source (2008) = 9.9 PgC/yr

  25. FOSSIL FUEL EMISSIONS: US vs CHINA IN 2001

  26. CHINA IS NOW THE WORLD’S LARGEST EMITTER OF CO2 Population of China (1.3B) is more than 4x the US (307M). Per capita emissions are still 4 times higher in the US. US and China together currently make up 41% of global CO2 emissions

  27. ~ 2º K in 2100 CARBON-CLIMATE FUTURES Coupled simulations of climate and the carbon cycle Vegetation matters! Different models project dramatically different futures using different ecosystem models.

  28. PROJECTED FUTURE TRENDS IN CO2 UPTAKEBY OCEANS AND TERRESTRIAL BIOSPHERE IPCC [2001]

  29. PROJECTIONS OF FUTURE CO2 CONCENTRATIONS [IPCC SRES]

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