1. Simulations of historical and future anthropogenic CO 2 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 Caldeira Lawrence Livermore National Laboratory, USA Sixth International Carbon Dioxide Conference 5 October 2001

2. Main points Some agreement on global historical CO 2 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 Boundary conditions Sub-grid mixing Mixed Layer Sea-ice Model Offline/Online

5. 230022002000190018002100 Atmospheric CO 2 scenarios Models were run with specified atmospheric CO 2 boundary conditions No future climate change

6. Models largely agree on the historical global anthropogenic CO 2 flux 20001950190018501800

7. Summary of results for ocean uptake of anthropogenic CO 2

8. Rationale for CO 2 uptake estimate Observed natural ∆ 14 C values are within the range of model results. –Modeled CO 2 uptake is correlated with modeled ∆ 14 C Observed CFC-11 concentrations are within the range of model results –Modeled CO 2 uptake is correlated with modeled [CFC-11] Independently estimated anthropogenic CO 2 inventories are within the range of model results Therefore, anthropogenic CO 2 uptake by the real ocean is probably within the range of model results. –Ocean CO 2 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 1995 anthropogenic CO 2 fluxes Regional anthropogenic CO 2 fluxes differ, especially in the Southern Ocean

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

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

12. Anthropogenic CO 2 uptake is correlated with ∆ 14 C and CFC uptake CFC-11 uptake∆ 14 C

13. Data-based estimate Simulated 1995 anthropogenic CO 2 column inventories Some models take up little CO 2 in the Southern Ocean Some models take up a lot of CO 2 in the Southern Ocean Sabine et al., 2001

14. Simulated 1995 cumulative CO 2 fluxes and inventory Large model differences in the Southern Ocean

15. Eq80 S80 N40 N40 S Southern Ocean more important later in century in some models Zonal Integral Air-to-Sea CO 2 Flux (IPSL)

16. Agreement in the past Model results for ocean CO 2 uptake Less agreement in the future

17. Model results for ocean CO 2 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 CO 2 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 ∆ 14 C values are within the range of model results. Modeled CO 2 uptake is correlated with modeled ∆ 14 C –Observed CFC-11 concentrations are within the range of model results Modeled CO 2 uptake is correlated with modeled [CFC-11] –Independently estimated anthropogenic CO 2 inventories are within the range of model results –Therefore, anthropogenic CO 2 uptake by the real ocean is probably within the range of model results. Models predictions differ for both regional and future CO 2 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 CO 2 uptake Southern Ocean (< 40°S) and remainder of ocean each explain about 50% of inter-model variance in global ocean CO 2 uptake

25. Southern Ocean and global CO 2 uptake CO 2 uptake in Southern Ocean (< 40°S) and remainder of ocean are not correlated

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