ATOC 220Global Carbon Cycle

• Recent change in atmospheric carbon

• The global C cycle and why is the contemporary atmospheric C increasing?

• How much of the excess C do the oceans and terrestrial biosphere take up?

• How is C ultimately removed?Nigel Roulet, Geography (nigel.roulet@mcgill.ca)

November 10, 2008

(Petit et al. 1999)

Why is the contemporary

atmospheric carbon increasing?

Black: pre-industrial Red: + industrial era up to ~1990

Sedimentary rock40,000,000 (CaCO3)

(IPCC, 2006)

Global Carbon Cycle

Historical Land Use Maps (RIVM, Netherlands)

Kees Klein Goldewijk (2001)

CO2 source/sink equation

uselandfflandoceans FFFFCCO _2

3.2 = -2.2 – 2.6 + 6.4 + 1.6

IPCC 2006 best guess

sink sink source source

(Sarmiento and Gruber, 2002)

atmospheric CO2

ocean

land

fossil fuel emissions

deforestation

7.6

1.5

4.1

2.22.8

2000-2006

CO2 f

lux

(Pg

C y-1

)Si

nkSo

urce

Time (y)

Perturbation of Global Carbon Budget (1850-2006)

Le Quéré, unpublished; Canadell et al. 2007, PNAS

Fossil Fuel Emissions: Actual vs. IPCC Scenarios

Raupach et al 2007, PNAS & Global Carbon Project update (http://www.globalcarbonproject.org/carbontrends/index.htm)

Observed

2000-2007 3.5%

2007 Fossil Fuel: 8.5 Pg C

Raupach et al 2007, PNAS

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

1980

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

1980

World

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

1980 1985 1990 1995 2000 2005

F (emissions)P (population)g = G/Ph = F/G

Fact

or (r

elat

ive to

199

0)

EmissionsPopulationWealth = per capita GDPCarbon intensity of GDP

Drivers of Anthropogenic Emissions

Why are the oceans and terrestrial ecosystems taking up excess CO2?

1. The marine biological pump

Deep Ocean

Ocean surface

atmospheric CO2

Phytoplankton

sedimentationof organic C

BacterialdecompositionCO2

Nutrients

upwelling

Ocean net primary production

Global Ocean NPP ~ 50 to 60 Gt C/yr → ~ 11 buried & the rest recycled

Living biomass is 3 Gt C it means the residence time of the plankton is a few weeks

NP

P g

C/m

2 /yr

2. The solubility pump

Ocean surfaceAtmosphere

H2CO3 H+ + HCO3-

HCO3- H+ + CO3

2-

CO2

CO2 + H2O H2CO3

bicarbonate

carbonate

carbonic acid

2. The solubility pump

Ocean surfaceAtmosphere

H2CO3 H+ + HCO3-

HCO3- H+ + CO3

2-

CO2

CO2 + H2O H2CO3

bicarbonate

carbonate

carbonic acid

How is this CO2 removed from contact with the

atmosphere?

How is this CO2 removed from contact with the

atmosphere?

Thermohaline circulation

CO2(aq) dissociates rapidly into DIC while increasing acidity: pH

K1 K2

CO2 + H2O HCO3- + H+ CO3

2- + 2H+

Bjerrum Plot:pH = 8.1

T = 250C, S = 35 [CO2] : [HCO3

-] : [CO3=]

0.5% : 86.5% : 13%

=> Buffering?? (Zeebe & Wolf-Gladrow,

2002)

bicarbonate carbonate

Ocean Acidity

Observations

Model analysisCalderia & Wickett

http://royalsociety.org/displaypagedoc.asp?id=13314

Ocean surfaceAtmosphere

H2CO3 H+ + HCO3-

CO2

CO2 + H2O H2CO3

Ca2+ + 2HCO3- CaCO3 + H2CO3

shelled organisms

The solubility pump &calcium carbonate formation

Coccolithophores (algae)• planktonic• produce 1.5 million tons of CaCO3 per yr• sometimes form “blooms” at the ocean surface which reflect visible light

SeaWiFS image 16 July 2000

CO2

600

1700

~120 ~60

~60~60

Gross primary production

(GPP)

AutotrophicRespiration (AR)

HeterotrophicRespiration (HR)

Net ecosystem production ( > 0)NEP = NPP - HR

The ‘real’ terrestrial C cycle

Store

Time (longer)

Disturbance ?

Forest Regrowth

Pool changes were evaluated as the difference between the late 1990s and early 1980s pool estimates, pixel-by-pixel, and quoted on a per year basis.The carbon pool in the woody biomass of northern forests (1.5 billion ha) is estimated to be 61 20 Gt C during the late 1990s.

Our sink estimate for the woody biomass during the 1980s and 1990s is 0.680.34 Gt C/yr.http://cybele.bu.edu/greeningearth/ge.html

Why an increased uptake on land?

• Elevated CO2 leading to increased NPP– Evidence suggest this might be only a few

percent• Response to increased nitrogen

deposition– Evidence indicates that only a small fraction

of added N getting into biomass: most is immobilized in soils

• Climate change?• Forest regrowth

– Most reasonable explanation• Detail inventory studies in the US support this• Remote sensing estimates support increase in

biomass

(K.R. Gurney et al., Nature, 415:626 [2002])

What are the relative importance of the land and

oceans in taking up excess CO2?

Sou

rce

Sin

k

Many model inversions using lots of data

The Efficiency of Natural Sinks: Land and Ocean Fractions

Land

Ocean

Canadell et al. 2007, PNAS

Rel

ativ

e to

an

nual

atm

osph

eric

inp

ut

The ultimate sink – the ocean floor – slow but

steady

161 Gt C 0.2 Gt C/yr

= 805 years

Key point

It takes a very long time to get

the excess carbon out of

the atmosphere

So we have this all figured out!

Vulnerabilities of the Carbon-Climate-Human system

Atmospheric CO2

Fossil Fuel burning

Vulnerability of C pools

WARMING

(+)

C emissions

(+)

(+)(+)

(+)

Carbon-climate System

(-)

Carbon-climate-human System

XEnergySystems

Human Actions

Social Structuresand Institutions

Human System

(+)

IMPACTS - ADAPTATION

(-)

LUCSystems