Global Carbon Cycling Where does it all go?

1. Global Carbon CyclingWhere does it all go?

2. Main Concepts Current CO2 levels: fluxes in and out What are C reservoirs? Natural CO2 sources and sinks: The land breathes. The ocean breathes. The rocks breathe. Carbon Residence time? Timescales of carbon removal from the atmosphere.

3. Atmospheric CO2 What are the major sources of C emissions? How unique are modern CO2 levels? Where does it all go? How long will it stick around?

4. Fossil fuel CO2 emissions: Burning buried sunshine

5. Carbon emissions rising faster than estimates

7. Global C emissions map Where emissions come from

8. Atmospheric CO2:Last 50 years (2.0 ppm/year increase, or 0.5%) 391 ppm

9. It’s alive! Seasonal cycle

10. CO2 growth rates http://www.esrl.noaa.gov/gmd/webdata/ccgg/trends/co2_data_mlo_anngr.png

11. CO2 growth rates http://www.esrl.noaa.gov/gmd/webdata/ccgg/trends/co2_data_mlo_anngr.png

12. What do we know aboutgreenhouse gases and past climate change?

13. Trapped air Glacial ice “traps” ancient air Free air Snow accumulates… Snow becomes ice Pore spaces are sealed and they trap ambient air. Up to 800,000 year old ice… with ancient trapped air bubbles!

14. Atmospheric CO2: Last 250 years

15. Atmospheric CO2: last 400,000 years!

16. Atmospheric CO2:Last 50 MILLION years How unusual are modern CO2 levels?

17. Carbon fluxes (in Gt/yr), reservoirs (bold, Gt), and residence times (years) 1990s data Note: 2010 emissions were 9 Gt / year

18. How much is a gigaton (Gt)? • One billion metric tons (1012 kg) • It is about 2750 Empire State Buildings. • Global C emissions are about 9 Gt as of 2010. How much does global population weigh?

19. Natural vs. human carbon fluxes Negative (positive) means removed from (added to) theatmosphere; 2002 data)

20. Carbon ins and outs Source: Carbon Emissions: 7 Gt/year Deforestation: 2 Gt/year Sink: Obs. Atm increase: -4 Gt/year Ocean uptake: -2.5 Gt/year “missing sink”: -2.5 Gt/year 2002 data

21. Human Carbon emissions 2012 emissions are ~9 Gt… were about 6 Gt when I started teaching this course !

22. Deforestation accounts for an additional +2 Gt / year Deforestation - Mainly tropical rainforests - Cutting down forests to make agricultural land is a net source of carbon to the atmosphere. CH2O + O2 CO2 + H2O Bolivia (1984-1998)

23. Where do our carbon emissions go? • Ocean takes up about -2.5 Gt / year • Roughly one-third of our fossil fuel emissions Air (CO2) CO2 + H2O  H+ + HCO3- Oceanic “Buffer reaction” Sea (CO2)

24. Why does the ocean take up CO2? CO2 gas is soluble in the ocean • Gas solubility is highest in colder water • CO2 enters the oceans at the poles • CO2 is converted to HCO3- by “buffer reaction” • The ocean acidifies as a direct result Ocean “buffer chemistry” can take up only a finite amount of CO2.

25. Air-Sea CO2 fluxes Gases are more soluble in COLD water Ocean uptake Net: -2 Gt/yr Ocean release Ocean uptake Ocean uptake Ocean release

26. Where is our carbon in the oceans ? Vertical Sections through the oceans Total ocean uptake is about -2.5 Gt / year

27. Carbon ins and outs Source: Carbon Emissions: 7 Gt/year Deforestation: 2 Gt/year Sink: Obs. Atm increase: -4 Gt/year Ocean uptake: -2.5 Gt/year “missing sink”: -2.5 Gt/year 2002 data

28. What is the “missing sink” The “missing sink” is the amount of carbon required to balance sources and sinks. It is a big number: -2.5 Gt Carbon / year ! What is it ???

29. The Missing Sink (history)

30. Missing C sink: 1-2 Gt CO2 fertilization “CO2 fertilization” of high-latitude forests Plants grow faster/better at higher CO2 But … the effect is assymptotic (not linear) Plant C uptake Atm CO2 level

31. Other things we need to know • Not only Fluxes of carbon in/out (Gt / year) • Sizes of the carbon reservoirs • Residence Time of carbon in each reservoir • These additional factors determine who the biggest players are and how quickly they will act.

32. Why these things matter • What would happen to CO2 levels if we stopped all emissions today? • What if the ocean warms up a lot? • What if deep ocean circulation were to change ? • Does Arbor day matter ?

33. Ocean and Atmoshere C reservoirs Atmosphere: 1580 Gt (as CO2) Ocean C: 39,000 Gt (as HCO3-, CO32-) Ocean has 50x more carbon than the atmosphere.

34. 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

35. 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 (surface only) = ? C residence time (whole ocean) = ?

36. The fate of fossil fuel CO2 Q: How quickly will the planet take up our CO2? A: Not very quickly… Fast: “solubility pump” Air-Sea CO2 exchange (centuries) Moderate: “Deep ocean acid neutralization” (tens of thousands of years) Really slow: “Weathering of continental rocks” (millions of years)

37. Fastest response (decades to centuries): The CO2 solubility pump Air-Sea gas exchange

38. Medium response time (104 years): Neutralize ocean acidity Neutralize deep ocean acidity by Dissolving ocean CaCO3 sediments CaCO3 Ca2+ + CO32-

39. Really Slow response time (106 years) Continental weathering (dissolves mountains!) “Urey reaction” - millions of years CaSiO3 + CO2 --> CaCO3 + SiO2

40. 75% in 300 years 25% “forever”

41. Bottom Line Human C Emissions are large Nature can’t keep up Natural C sinks are diminishing Lifetime of CO2 from your tailpipe: “300 years, plus 25% that lasts forever”

42. Radiative Forcing • Helps us quantify how global climate responds to an imposed change (“forcing”).

43. What is Radiative Forcing? Radiative forcing: An imposed change in Earth’s radiative energy balance. Measured in Watts per square meter (W/m2) • “Radiative” because these factors change the balance between incoming solar radiation and outgoing infrared radiation within the Earth’s atmosphere. This radiative balance sets the Earth’s surface temperature. • “Forcing” indicates that Earth’s radiative balance is being pushed away from its normal state. Examples: Solar variability, volcanic emissions, greenhouse gases, ozone, changes in ice cover (albedo), land use changes.

44. Our first climate model Recall how to calculate Earth’s effective temperature The Stefan-Bolzmann equation: Blackbody radiation I (w/m2) = s T4 Earth incoming radiation (a = Earth albedo, or reflectivity) I incoming = (1-a) Isolar = (1-a) s Tsun4 a Is ~0.3, or 30%

45. Our first climate model Earth incoming radiation (a = Earth albedo, or reflectivity) I incoming = ((1-a) Isolar ) / 4, or ((1-a) s Tsun4 )/ 4 Earth outgoing radiation I outgoing = s Tearth4

46. Earth’s temperature with no greenhouse effectTeffective = 254.8K (-18°C) At equilibrium, I incoming = I outgoing Set Sunlight = Earthlight Solve for Tearth Eqn. 3.1 in Archer Chapter 3

47. Volcanic eruption can change albedo by 1%  = ~30% on average Teffective = 254.8K Increase  to 31% New Teffective = 253.9K or -1°C cooler due a volcanic eruption Recalling I = (1-a) s T4

48. Adding an atmosphere

49. Greenhouse gases are “selective absorbers”of outgoing long wavelength radiation (Earthlight) Spectrum of IR light emitted from earth to space

50. Water Vapor Molecule (H2O)Vibrational modes H2O stretch H2O bend