Simulations of historical and future anthropogenic CO 2 uptake from 12 global ocean models

1. Sixth International Carbon Dioxide Conference 5 October 2001 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

2. 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)

3. 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

4. The models differ Resolution Seasonality Boundaryconditions Sub-grid mixing Mixed Layer Sea-ice Model Offline/Online

5. Atmospheric CO2 scenarios Models were run with specified atmospheric CO2 boundary conditions No future climate change 1800 1900 2000 2100 2200 2300

6. Models largely agree on the historical global anthropogenic CO2 flux 1800 1850 1900 1950 2000

7. Summary of results for ocean uptake of anthropogenic CO2

8. 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

9. Simulated 1995anthropogenic CO2 fluxes Regional anthropogenic CO2 fluxes differ, especially in the Southern Ocean

10. Data Pacific OceanWOCE P16 14C Some models over-predict 14C Some models under-predict 14C

11. CFC-11 in the South Atlantic Ajax Data Some models under-predict CFC uptake Some models over-predict CFC uptake Dutay et al., 2001

12. Anthropogenic CO2 uptake is correlated with ∆14C and CFC uptake ∆14C CFC-11 uptake

13. Sabine et al., 2001 Data-based estimate Simulated 1995anthropogenic CO2 columninventories Some models take up a lot of CO2 in the Southern Ocean Some models take up little CO2 in the Southern Ocean

14. Large model differences in the Southern Ocean Simulated 1995 cumulative CO2 fluxes and inventory

15. Southern Ocean more important later in century in some models Zonal Integral Air-to-Sea CO2 Flux (IPSL) 80 S 40 S Eq 40 N 80 N

16. Model results for ocean CO2 uptake Less agreementin the future Agreementin the past

17. 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)

18. 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

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

20. 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

21. 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

23. Anthropogenic CO2 vs. CFC-11 Gruber et al., 2001

24. 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

25. Southern Ocean and global CO2 uptake • CO2 uptake in Southern Ocean (< 40°S) and remainder of ocean are not correlated

29. Natural 14Con the W. Atlantic GEOSECS Some models under-predict 14C Some models over-predict 14C