# Uncertainties due to transport-parameter sensitivity in an efficient 3-D ocean-climate model

- 602 Downloads
- 101 Citations

## Abstract

A simplified climate model is presented which includes a fully 3-D, frictional geostrophic (FG) ocean component but retains an integration efficiency considerably greater than extant climate models with 3-D, primitive-equation ocean representations (20 kyears of integration can be completed in about a day on a PC). The model also includes an Energy and Moisture Balance atmosphere and a dynamic and thermodynamic sea-ice model. Using a semi-random ensemble of 1,000 simulations, we address both the inverse problem of parameter estimation, and the direct problem of quantifying the uncertainty due to mixing and transport parameters. Our results represent a first attempt at tuning a 3-D climate model by a strictly defined procedure, which nevertheless considers the whole of the appropriate parameter space. Model estimates of meridional overturning and Atlantic heat transport are well reproduced, while errors are reduced only moderately by a doubling of resolution. Model parameters are only weakly constrained by data, while strong correlations between mean error and parameter values are mostly found to be an artefact of single-parameter studies, not indicative of global model behaviour. Single-parameter sensitivity studies can therefore be misleading. Given a single, illustrative scenario of CO_{2} increase and fixing the polynomial coefficients governing the extremely simple radiation parameterisation, the spread of model predictions for global mean warming due solely to the transport parameters is around one degree after 100 years forcing, although in a typical 4,000-year ensemble-member simulation, the peak rate of warming in the deep Pacific occurs 400 years after the onset of the forcing. The corresponding uncertainty in Atlantic overturning after 100 years is around 5 Sv, with a small, but non-negligible, probability of a collapse in the long term.

## Keywords

Antarctic Circumpolar Current Couple Model Intercomparison Project Freshwater Flux Initial Ensemble Deep Temperature## Notes

### Acknowledgements

We thank J.D. Annan for helpful comments on statistical analysis and Jeff Blundell for help in processing ETOPO5 data. The modification to Hibler’s sea ice-area equation was suggested by Masakazu Yoshimori. NRE is supported by the Swiss NCCR-Climate programme. RM acknowledges the support of the UK NERC Earth System Modelling Initiative.

## References

- Annan JD, Hargreaves JC, Edwards NR, Marsh R (2005) Parameter estimation in an intermediate complexity earth system model using an ensemble Kalman filter. Ocean Model 8:135–154CrossRefGoogle Scholar
- Boville BA, Gent PR (1998) The NCAR climate system model, version one. J Clim 11:1115–1130CrossRefGoogle Scholar
- Edwards NR, Shepherd JG (2001) Multiple thermohaline states due to variable diffusivity in a hierarchy of simple models. Ocean Model 3:67–94CrossRefGoogle Scholar
- Edwards NR, Shepherd JG (2002) Bifurcations of the thermohaline circulation in a simplified three-dimensional model of the world ocean and the effects of interbasin connectivity. Clim Dyn 19:31–42CrossRefGoogle Scholar
- Edwards NR, Willmott AJ, Killworth PD (1998) On the role of topography and wind stress on the stability of the thermohaline circulation. J Phys Oceanogr 28:756–778CrossRefGoogle Scholar
- Goosse H, Selten FM, Haarsma RJ, Opsteegh JD (2001) Decadal variability in high northern latitudes as simulated by an intermediate-complexity climate model. Ann Glaciol 33:525–532Google Scholar
- Gordon C, Cooper C, Senior CA, Banks H, Gregory JM, Johns TC, Mitchell JFB, Wood RA (2000) The simulation of SST, sea-ice extents and ocean heat transports in a version of the Hadley Centre coupled model without flux adjustments. Clim Dyn 16:147–168CrossRefGoogle Scholar
- Griffies SM (1998) The Gent-McWilliams skew flux. J Phys Oceanogr 28:831–841CrossRefGoogle Scholar
- Hall MM, Bryden HL (1982) Direct estimates and mechanisms of ocean heat transport. Deep-Sea Res 29:339–359CrossRefGoogle Scholar
- Hargreaves JC, Annan JD, Edwards NR, Marsh R (2005) Climate forecasting using an intermediate complexity Earth System Model and the Ensemble Kalman Filter. Clim Dyn (in press).Google Scholar
- Hibler WD (1979) Dynamic thermodynamic sea ice model. J Phys Oceanogr 9:815–846CrossRefGoogle Scholar
- Hogg AMcC, Dewar WK, Killworth PD, Blundell JR (2003) A quasi-geostrophic coupled model: Q-GCM. Mon Weather Rev 131:2261–2278CrossRefGoogle Scholar
- Holland DA, Mysak LA, Manak DK (1993) Sensitivity study of a dynamic thermodynamic sea ice model. J Geophys Res 97:5365–2586Google Scholar
- Jia Y (2003) Ocean heat transport and its relationship to ocean circulation in the CMIP coupled models. Clim Dyn 20:153–174Google Scholar
- Josey SA, Kent EC, Taylor PK (1998) The Southampton Oceanography Centre (SOC) Ocean-Atmosphere Heat, Momentum and Freshwater Flux Atlas. Southampton Oceanography Centre Rep. 6, Southampton, United Kingdom, 30 pp + figuresGoogle Scholar
- Killworth PD (2003) Some physical and numerical details of frictional geostrophic models. Southampton Oceanography Centre internal report 90Google Scholar
- Knutti R, Stocker TF, Joos F, Plattner G-K (2002) Constraints on radiative forcing and future climate change from observations and climate model ensembles. Nature 416:719–723CrossRefPubMedGoogle Scholar
- Levitus S, Boyer TP, Conkright ME, O’Brien T, Antonov J, Stephens C, Stathoplos L, Johnson D, Gelfeld R (1998) Noaa Atlas Nesdis 18, World ocean database 1998, vol. 1, Introduction, US Government Printing Washington DC, 346ppGoogle Scholar
- Marsh R, Yool A, Lenton TM, Gulamali MY, Edwards NR, Shepherd JG, Krznaric M, Newhouse S, Cox SJ (2005) Bistability of the thermohaline circulation identified through comprehensive 2-parameter sweeps of an efficient climate model. Clim Dyn (in press)Google Scholar
- McPhee MG (1992) Turbulent heat flux in the upper ocean under sea ice. J Geophys Res 97:5365–5379Google Scholar
- Millero FJ (1978) Annex 6, freezing point of seawater. Unesco technical papers in the marine sciences 28:29–35Google Scholar
- Oort AH (1983) Global atmospheric circulation statistics, 1958–1973:NOAA Prof Pap 14Google Scholar
- Petoukhov V, Ganopolski A, Brovkin V, Claussen M, Eliseev A, Kubatzki C, Rahmstorf S (2000) CLIMBER-2: a climate system model of intermediate complexity. Part I: model description and performance for present climate. Clim Dyn 16:1–17Google Scholar
- Roemmich D, Wunsch C (1985) Two transatlantic sections: meridional circulation and and heat flux in the subtropical North Atlantic Ocean. Deep-Sea Res 32:619–664CrossRefGoogle Scholar
- Semtner AJ (1976) Model for thermodynamic growth of sea ice in numerical investigations of climate. J Phys Oceanogr 6:379–389CrossRefGoogle Scholar
- Sinha B, Smith RS (2002) Development of a fast Coupled General Circulation Model (FORTE) for climate studies, implemented using the OASIS coupler. Southampton Oceanography Centre Internal Document, No 81:67Google Scholar
- Thompson SL, Warren SE (1982) Parameterization of outgoing infrared radiation derived from detailed radiative calculations. J Atoms Sci 39:2667:2680Google Scholar
- Trenberth KE, JM Caron (2001) Estimates of meridional atmosphere and ocean heat transports. J Climate 14:3433–3443CrossRefGoogle Scholar
- Weaver AJ, Eby M, Wiebe EC, Bitz CM, Duffy PB, Ewen TL, Fanning AF, Holland MM, MacFadyen A, Matthews HD, Meissner KJ, Saenko O, Schmittner A, Wang H, Yoshimori M (2001) The UVic Earth System Climate Model: model description, climatology, and applications to past, present and future climates. Atmos-Ocean 39:361–428Google Scholar
- Wright DG, Stocker TF (1991) A zonally averaged ocean model for the thermohaline circulation. Part I: model development and flow dynamics. J Phys Oceanogr 21:1713–1724CrossRefGoogle Scholar
- Zaucker F, Broecker WS (1992) The influence of atmospheric moisture transport on the fresh water balance of the Atlantic drainage basin: General Circulation Model simulations and observations. J Geophys Res 97:2765–2773Google Scholar