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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 ([email protected])
November 10, 2008
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(Petit et al. 1999)
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Why is the contemporary
atmospheric carbon increasing?
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Black: pre-industrial Red: + industrial era up to ~1990
Sedimentary rock40,000,000 (CaCO3)
(IPCC, 2006)
Global Carbon Cycle
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Historical Land Use Maps (RIVM, Netherlands)
Kees Klein Goldewijk (2001)
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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
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(Sarmiento and Gruber, 2002)
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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Le Quéré, unpublished; Canadell et al. 2007, PNAS
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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
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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
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Why are the oceans and terrestrial ecosystems taking up excess CO2?
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1. The marine biological pump
Deep Ocean
Ocean surface
atmospheric CO2
Phytoplankton
sedimentationof organic C
BacterialdecompositionCO2
Nutrients
upwelling
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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
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2. The solubility pump
Ocean surfaceAtmosphere
H2CO3 H+ + HCO3-
HCO3- H+ + CO3
2-
CO2
CO2 + H2O H2CO3
bicarbonate
carbonate
carbonic acid
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2. The solubility pump
Ocean surfaceAtmosphere
H2CO3 H+ + HCO3-
HCO3- H+ + CO3
2-
CO2
CO2 + H2O H2CO3
bicarbonate
carbonate
carbonic acid
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How is this CO2 removed from contact with the
atmosphere?
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How is this CO2 removed from contact with the
atmosphere?
Thermohaline circulation
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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
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Ocean Acidity
Observations
Model analysisCalderia & Wickett
http://royalsociety.org/displaypagedoc.asp?id=13314
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Ocean surfaceAtmosphere
H2CO3 H+ + HCO3-
CO2
CO2 + H2O H2CO3
Ca2+ + 2HCO3- CaCO3 + H2CO3
shelled organisms
The solubility pump &calcium carbonate formation
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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
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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 ?
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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
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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
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(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
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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
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The ultimate sink – the ocean floor – slow but
steady
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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
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So we have this all figured out!
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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
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