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Simulations of historical and future anthropogenic CO2 uptake from 12
global ocean models
J.C. Orr, P. Monfray, O. Aumont, A. Yool, I. Totterdell , K. Plattner, F. Joos, E. Maier-Reimer, M.-F. Weirig, R. Schlitzer, K. Caldeira, M. Wickett, R. Matear, M. Follows, Y. Gao, H. Drange, A. Ishida, Y. Yamanaka, S. Doney, K. Lindsay,
J.L. Sarmiento, R.D.Slater, R.M. Key, N. Gruber, C. Sabine and R. Najjar
http://www.ipsl.jussieu.fr/OCMIP
Presented by Ken CaldeiraLawrence Livermore National Laboratory, USA
Sixth International Carbon Dioxide Conference5 October 2001
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Main points
• Some agreement on global historical CO2 uptake by the ocean– For the 1980’s = 2.0 ± 0.4 PgC yr–1
– For the 1990’s – IS92a = 2.5 PgC yr–1
– adjusted IS92a = 2.2 PgC yr–1
• Some disagreement on regional and future fluxes– 1980’s and 1990’s +/-13% (about the mean)
– Year 2100 +/-20% (IS92a and S650)
– Year 2300 +/-35% (S650)
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OCMIP participants
• AWI (Alfred Wegener Institute for Polar and Marine Research), Bremerhaven, Germany
• CSIRO, Hobart, Australia • IGCR/CCSR, Tokyo, Japan • IPSL, (Institute Pierre Simon LaPlace), Paris, France • LLNL, Livermore, California, USA • MIT, Boston, MA, USA • MPIM, (Max Planck Institut fuer Meteorologie - Hamburg) Germany • NCAR, (National Center for Atmospheric Research), Boulder, Colorado, USA • NERSC, (Nansen Environmental and Remote Sensing Center), Bergen,
Norway • PIUB, (Physics Institute, University of Bern), Switzerland • PRINCEton (Princeton University [AOS, OTL] / GFDL), Princeton NJ, USA • SOC (Southampton Oceanography Centre) / SUDO / Hadley Center (UK Met.
Office), England • UL (University of Liege) /UCL (University Catholique de Louvain), Belgium
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The models differ
Resolution
Seasonality
Boundaryconditions
Sub-grid mixing
Mixed Layer
Sea-ice Model
Offline/Online
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23002200200019001800 2100
Atmospheric CO2 scenarios
Models were run with specified atmospheric CO2 boundary conditions
No future climate change
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Models largely agree on the historical global anthropogenic CO2 flux
20001950190018501800
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Summary of results for ocean uptake of anthropogenic CO2
Model 1980-1989 IS92a1990-1999*
Adjusted IS92a1990-1999*
PRINCE 1.65 2.15 1.9LLNL 1.78 2.22 1.9CSIRO 1.78 2.32 2.0MIT 1.91NCAR 1.93 2.50 2.2IPSL 2.03 2.63 2.3MPIM 2.01 2.60 2.3SOC 2.01 2.62 2.3IGCR 2.07 2.70 2.4AWI 2.14 2.75 2.4PIUB 2.18 2.82 2.5NERSC 2.38Mean ± Std Dev 1.99 ± 0.20 2.53 ± 0.23 2.2 ± 0.2Range 1.65 — 2.38 2.15 — 2.82 1.9 — 2.5
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Rationale for CO2 uptake estimate
• Observed natural ∆14C values are within the range of model results. – Modeled CO2 uptake is correlated with modeled ∆14C
• Observed CFC-11 concentrations are within the range of model results
– Modeled CO2 uptake is correlated with modeled [CFC-11]
• Independently estimated anthropogenic CO2 inventories are within the range of model results
• Therefore, anthropogenic CO2 uptake by the real ocean is probably within the range of model results.– Ocean CO2 uptake for the 1980’s = 2.0 ± 0.4 PgC yr–1
– IS92a 1990’s = 2.5 PgC yr–1
– Adjusted IS92a 1990’s = 2.2 PgC yr–1
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Simulated 1995anthropogenic
CO2 fluxes
Regional anthropogenic CO2 fluxes differ, especially in the Southern Ocean
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Pacific OceanWOCE P16 14C
Some models under-predict 14C
Some models over-predict 14C
Data
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CFC-11 in the South Atlantic
Dutay et al., 2001
Ajax Data
Some models under-predict CFC uptake
Some models over-predict CFC uptake
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Anthropogenic CO2 uptake is correlated with ∆14C and CFC uptake
CFC-11 uptake∆14C
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Data-basedestimate
Simulated 1995anthropogenic CO2 columninventories
Some models take up little CO2 in the Southern Ocean
Some models take up a lot of CO2 in the Southern Ocean
Sabine et al., 2001
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Simulated 1995 cumulativeCO2 fluxes and inventory
Large model differences in the Southern Ocean
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Eq80 S 80 N40 N40 S
Southern Ocean more important later in century in some models
Zonal Integral Air-to-Sea CO2 Flux (IPSL)
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Agreementin the past
Model results for ocean CO2 uptake
Less agreementin the future
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Model results for ocean CO2 uptake
• Differences about the mean increase as time progresses– 1980’s and 1990’s +/-13%
– Year 2100 +/-20% (IS92a and S650)
– Year 2300 +/-35% (S650)
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Conclusions
• Ocean CO2 uptake for the 1980’s = 2.0 ± 0.4 PgC yr–1
• IS92a 1990’s = 2.5 PgC yr–1
• adjusted IS92a 1990’s = 2.2 PgC yr–1
– Observed natural ∆14C values are within the range of model results. • Modeled CO2 uptake is correlated with modeled ∆14C
– Observed CFC-11 concentrations are within the range of model results • Modeled CO2 uptake is correlated with modeled [CFC-11]
– Independently estimated anthropogenic CO2 inventories are within the range of model results
– Therefore, anthropogenic CO2 uptake by the real ocean is probably within the range of model results.
• Models predictions differ for both regional and future CO2 uptake
– Differences between models increase as time progresses
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http://www.ipsl.jussieu.fr/OCMIP
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Which model is the best?
• Many model deficiencies can be corrected by simple model tuning– e.g., adjustment of turbulent mixing coefficients within
observationally defensible values
• The intrinsically “best” model may perform poorly due to inadequate tuning
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Which model is the best?• OCMIP2 did not determine which model is intrinsically best
– The models that performed well may reflect model tuning and not necessarily intrinsic superiority
– For example, many believe that isopycnal models may be intrinsically better, but the NERSC configuration of the MICOM model was not tuned
• Which screwdriver is best depends on which kind of screw you have– Different models types (e.g., inverse, forward, 3-D/2-D,
offline/online, coarse/high-resolution, etc.) are designed for different purposes
– OCMIP developed a reference database that you can use to determine which model is best for your purposes
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Anthropogenic CO2 vs. CFC-11
Gruber et al., 2001
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Southern Ocean and global CO2 uptake
• Southern Ocean (< 40°S) and remainder of ocean each explain about 50% of inter-model variance in global ocean CO2 uptake
y = 1.0064x + 1.9865R2 = 0.5067
2.4
2.5
2.6
2.7
2.8
2.9
3
3.1
3.2
0.7 0.8 0.9 1 1.1 1.2
Southern Ocean CO2 Uptake (PgC/yr)
Global Ocean CO2 Uptake (Pgc/yr)
y = 1.0065x + 0.8625R2 = 0.4998
2.4
2.5
2.6
2.7
2.8
2.9
3
3.1
3.2
1.7 1.8 1.9 2 2.1 2.2 2.3
Equatorial and Northern CO2 Uptake (PgC/yr)
Global Ocean CO2 Uptake (Pgc/yr)
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Southern Ocean and global CO2 uptake
• CO2 uptake in Southern Ocean (< 40°S) and remainder of ocean are not correlated
y = 0.0065x + 0.8625R2 = 4E-05
0.6
0.7
0.8
0.9
1
1.1
1.2
1.7 1.8 1.9 2 2.1 2.2 2.3
Equatorial and Northern CO2 Uptake (PgC/yr)
Southern Ocean CO2 Uptake
(Pgc/yr)
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Natural 14C on theW. Atlantic GEOSECS
Some models over-predict 14C
Some models under-predict 14C