A comparison of climate response to different radiative forcings in three general circulation models: towards an improved metric of climate change
- 459 Downloads
In order to review, and possibly refine, the concept of radiative forcing as a suitable metric for climate change, the responses of three general circulation models to distinct forcing scenarios are compared. CO2, solar radiation, and O3 are added in different locations, whilst keeping the globally averaged radiative forcing constant at 1 Wm–2. The three models react differently to the forcings, as feedback mechanisms such as sea-ice albedo and clouds behave differently in each model. However, we find that their climate sensitivities λ (defined as the ratio of the globally averaged surface temperature change to the radiative forcing), normalised by the climate sensitivity for a control case (e.g. CO2 added globally), match each other to within 30% in most experiments. Moreover, the models indicate generic deviations of λ from the case of global CO2 perturbations: upper tropospheric O3 increases generally produce lower values of λ, while lower stratospheric O3 perturbations lead to higher values of λ, as found in some previous work. λ tends to be higher for extratropical forcings than tropical forcings; a phenomenon which can be partially accounted for by a new explanation based on the variation of the outgoing longwave radiation with latitude. Our results suggest that if the radiative forcing associated with some perturbation is multiplied by some factor accounting for the efficiency of that mechanism, then such modified forcings can be compared more robustly than the forcings themselves.
KeywordsOzone Climate Sensitivity Stratospheric Ozone Tropospheric Ozone Lower Stratosphere
This study is part of the METRIC project, which has been funded by the European Commission through the Fifth Framework Programme (project number EV2K-CT-1999-000021). We thank the referees for their many useful comments.
- Hansen J, Sato M, Ruedy R (1997) Radiative forcing and climate response. J Geophys Res 102: 6831–6864Google Scholar
- IPCC (1990) Climate change 1990 Cambridge University Press, London, UKGoogle Scholar
- IPCC (1994) Climate change 1994 Radiative forcing of climate change. Cambridge University Press, LondonGoogle Scholar
- IPCC (1995) Climate change 1995 Cambridge University Press, LondonGoogle Scholar
- IPCC (2001) Climate change 2001 Cambridge University Press, LondonGoogle Scholar
- Le Treut H, Li ZX (1991) Sensitivity of an atmospheric general circulation model to prescribed SST changes: feedback effects associated with the simulation of cloud optical properties. Clim Dyn 5: 175–187Google Scholar
- Roeckner E, Arpe K, Bengtsson L, Christoph M, Claussen M, Dümenil L, Esch M, Giorgetta M, Schlese M, Schulzweida U (1996) The atmospheric general circulation model ECHAM-4: model description and simulation of present-day climate. Max-Planck Institut für Meteorologie, Rep 218, ISSN 0937-1060, Hamburg, pp 90Google Scholar
- Sadourny R, Laval K (1994) January and July performance of the LMD general circulation model. In: Berger A, Nicolis C (eds) New perspectives in climate modelling. Elsevier, Amsterdam, pp 173–198Google Scholar
- Shine KP (2000) Radiative forcing of climate change. Space Sci Rev 94: 363–373Google Scholar
- Stuber N, Ponater M, Sausen R (2001b) Is the climate sensitivity to ozone perturbations enhanced by stratospheric water vapor feedback? Geophys Res Lett 28: 2887–2890Google Scholar
- WMO (1957) Meteorology – a three-dimensional science: second session of the commission for aerology, WMO Bull IV (4): 134–138Google Scholar