U.S. Carbon Cycle Science Program & Carbon Cycle Interagency Working Group
ATOC 220 Global Carbon Cycle Recent change in atmospheric carbon The global C cycle and why is the...
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Transcript of ATOC 220 Global Carbon Cycle Recent change in atmospheric carbon The global C cycle and why is the...
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
(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Le Quéré, unpublished; Canadell et al. 2007, PNAS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