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

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)

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

The models differ

Resolution

Seasonality

Boundaryconditions

Sub-grid mixing

Mixed Layer

Sea-ice Model

Offline/Online

23002200200019001800 2100

Atmospheric CO2 scenarios

Models were run with specified atmospheric CO2 boundary conditions

No future climate change

Models largely agree on the historical global anthropogenic CO2 flux

20001950190018501800

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

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

Simulated 1995anthropogenic

CO2 fluxes

Regional anthropogenic CO2 fluxes differ, especially in the Southern Ocean

Pacific OceanWOCE P16 14C

Some models under-predict 14C

Some models over-predict 14C

Data

CFC-11 in the South Atlantic

Dutay et al., 2001

Ajax Data

Some models under-predict CFC uptake

Some models over-predict CFC uptake

Anthropogenic CO2 uptake is correlated with ∆14C and CFC uptake

CFC-11 uptake∆14C

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

Simulated 1995 cumulativeCO2 fluxes and inventory

Large model differences in the Southern Ocean

Eq80 S 80 N40 N40 S

Southern Ocean more important later in century in some models

Zonal Integral Air-to-Sea CO2 Flux (IPSL)

Agreementin the past

Model results for ocean CO2 uptake

Less agreementin the future

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)

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

http://www.ipsl.jussieu.fr/OCMIP

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

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

Anthropogenic CO2 vs. CFC-11

Gruber et al., 2001

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)

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)

Natural 14C on theW. Atlantic GEOSECS

Some models over-predict 14C

Some models under-predict 14C