1. Global Carbon Cycling Where does it all go?

2. Main Concepts Current CO 2 levels: fluxes in and out What are C reservoirs? Natural CO 2 sources and sinks: The land breathes. The ocean breathes. The rocks breathe. Carbon Residence time? Timescales of carbon removal from the atmosphere.

3. Atmospheric CO 2 What are the major sources of C emissions? How unique are modern CO 2 levels? Where does it all go? How long will it stick around?

4. Fossil fuel CO 2 emissions: Burning buried sunshine

6. Global C emissions map

7. Atmospheric CO 2 :Last 50 years (1.5 ppm/year increase)

8. Atmospheric CO 2 : Last 250 years

9. Atmospheric CO 2 : last 400,000 years!

10. Atmospheric CO 2 : Last 50 MILLION years How unusual are modern CO2 levels?

11. Atmospheric CO 2 : Last 500 MILLION years

12. Estimating Ancient CO 2 : Leaf Stomata Stomata density related to CO 2 high CO 2 = low stomatal density Living Fossil

13. Carbon fluxes (in Gt/yr), reservoirs (bold, Gt), and residence times (years) Note: 2006 emissions were 7.7 Gt / year, as of 1990

14. How much is a gigaton (Gt)? One billion metric tons (10 15 g) It is about 2750 Empire State Buildings. Global C emissions are about 6 Gt.

15. Carbon cycle fluxes These have significant errors and change year-to-year CyclingFlux rate (Gt/year) Ocean uptake -2.0 Photosynthesis -120.0 Respiration +120.0 Fossil Fuel Combustion +6.0 Biomass burning +1.0 ( “-” means removed from atmosphere; 1990 data)

16. The atmosphere only contains about 2/3 of the total C emissions - why?

17. Carbon “sinks” Source: Carbon Emissions: 6.0 Gt/year Sink: Obs. Atm increase: 3.2 Gt/year Ocean uptake: 2.0 Gt/year “missing sink”: 1.8 Gt/year 1990 estimates

18. Ocean-Atmosphere gas exchange Vertical Sections through the oceans Air Sea CO 2 + H 2 O  H + + HCO 3 -

19. Air-Sea CO 2 fluxes Ocean uptake Ocean release Gases are more soluble in COLD water Ocean uptake Ocean release Net: -2 Gt/yr

20. Ocean and Atmoshere C reservoirs Ocean C: 39,000 Gt (as HCO 3 -, CO 3 2- ) Atmosphere: 1580 Gt (as CO 2 ) Ocean has 50x more carbon than the atmosphere.

21. Carbon Fluxes

22. Calculating Residence time Residence time is a “replacement time”: time required to affect a reservoir given a certain flux.  (years) = reservoir / input rate Example: Residence time of a CU undergrad Reservoir: Size of Columbia’s UG Student Body? Input rate: Incoming 1st-year class size

23. Calculating residence time of Carbon due to air-sea exchange Ocean uptake rate: -2.0 Gt / year Total Ocean C reservoir : 39,000 Gt Surface Ocean C reservoir : 600 Gt C residence time (whole ocean) = ? C residence time (surface only) = ?

24. Q1:

25. Carbon Cycle Budget At steady state: Sources = Sinks Sources: Respiration, FF, land use Sinks: Photosynthesis, ocean uptake But.. C is not at steady state… (CO 2 is rising, right? Equivalent to +3.2 x10 15 g/ year So the following should be true: +3.2 Gt/year = (Sources) + (Sinks)

26. The missing C sink (Gt/yr) +3.2 = (Sources) + (Sinks) + (other) +3.2 = (122+90+6+1) + (-120-92-2) + (other) +3.2 = (219 - 214) + (other) “other” = 5.0 - 3.2 “other” = missing sink of -1.8 Gt/year This “missing sink” has been removing C from atmosphere each year…(a good thing)

27. The Missing Sink (history)

28. Missing C sink: What is it? CO 2 fertilization of high-latitude forests Plants grow faster/better at higher CO 2 Atm CO 2 level Plant C uptake

29. Current state of the Missing Sink “Missing sink” was accelerated growth of northern forests under high CO 2 (carbon uptake) This sink is now completely offset by tropical deforestation. (additional carbon emission) Bolivia (1984-1998)

30. The future of fossil fuel CO 2 How quickly would the planet take up our CO 2 ? Fast: “solubility pump” Air-Sea CO 2 exchange (centuries) Moderate: “Deep ocean acid neutralization” (tens of thousands of years) Really slow: “Weathering of continental rocks” (millions of years)

31. Fast C cycling: Air-Sea Exchange Centuries

32. Moderate C Cycling Neutralize deep ocean acidity by Dissolving ocean CaCO 3 sediments 10 4 years

33. Really Slow C cycling Continental weathering (dissolves mountains!) “Urey reaction” - millions of years CaSiO 3 + CO 2 --> CaCO 3 + SiO 2

34. Carbon Reservoirs (1Gt = 10 15 g) ReservoirSize Rocks65,000,000 Oceans39,000 Soils1,580 Land Plants610

35. 75% in 300 years 25% “forever”

36. Bottom Line Human C Emissions are large Nature can’t keep up Natural C sinks are diminishing Lifetime of CO 2 from your tailpipe: “300 years, plus 25% that lasts forever”