Global Carbon CyclingWhere does it all go?

Main Concepts

Current CO2 levels: fluxes in and outWhat 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.

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?

Fossil fuel CO2 emissions: Burning buried sunshine

Global C emissions map

Atmospheric CO2:Last 50 years (1.5 ppm/year increase)

Atmospheric CO2: Last 250 years

Atmospheric CO2: last 400,000 years!

Atmospheric CO2:Last 50 MILLION years

How unusual are modern CO2 levels?

Atmospheric CO2:Last 500 MILLION years

Estimating Ancient CO2:Leaf Stomata

Stomata density related to CO2

high CO2 = low stomatal density

Living

Fossil

Carbon fluxes (in Gt/yr), reservoirs (bold, Gt), and residence times (years)

Note: 2006 emissions were 7.7 Gt / year,

as of 1990

How much is a gigaton (Gt)?

• One billion metric tons (1015 g)

• It is about 2750 Empire State Buildings.

• Global C emissions are about 6 Gt.

Carbon cycle fluxesThese have significant errors and change year-to-year

Cycling Flux 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)

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

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/year1990 estimates

Ocean-Atmosphere gas exchange

Vertical Sections through the oceans

Air

Sea

CO2 + H2O H+ + HCO3-

Air-Sea CO2 fluxes

Ocean uptake

Ocean release

Gases are more soluble in COLD water

Ocean uptake

Ocean uptake Ocean release

Net:-2 Gt/yr

Ocean and Atmoshere C reservoirs

Ocean C: 39,000 Gt (as HCO3-, CO3

2-)

Atmosphere: 1580 Gt (as CO2)

Ocean has 50x more carbon than the atmosphere.

Carbon Fluxes

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 undergradReservoir: Size of Columbia’s UG Student

Body?Input rate: Incoming 1st-year class size

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) = ?

Q1:

Carbon Cycle Budget

At steady state: Sources = Sinks

Sources: Respiration, FF, land useSinks: Photosynthesis, ocean uptake

But.. C is not at steady state… (CO2 is rising, right? Equivalent to +3.2 x1015g/ year

So the following should be true:+3.2 Gt/year = (Sources) + (Sinks)

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)

The Missing Sink (history)

Missing C sink: What is it?

CO2 fertilization of high-latitude forests

Plants grow faster/better at higher CO2

Atm CO2 level

Plant Cuptake

Current state of the Missing Sink

“Missing sink” was accelerated growth of northern forests under high CO2 (carbon uptake)

This sink is now completely offset by tropical deforestation. (additional carbon emission)

Bolivia (1984-1998)

The future of fossil fuel CO2

How quickly would the planet take up our CO2?

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)

Fast C cycling: Air-Sea Exchange

Centuries

Moderate C Cycling

Neutralize deep ocean acidity by Dissolving ocean CaCO3 sediments

104 years

Really Slow C cycling

Continental weathering (dissolves mountains!)“Urey reaction” - millions of yearsCaSiO3 + CO2 --> CaCO3 + SiO2

Carbon Reservoirs (1Gt = 1015g)

Reservoir Size

Rocks 65,000,000

Oceans 39,000

Soils 1,580

Land Plants 610

75% in 300 years

25% “forever”

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”