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  • Stone, D. A., M. R. Allen, F. Selten, M. Kliphuis, and P. A. Stott, 2007: The detection and attribution of climate change using an ensemble of opportunity. Journal of Climate, 20, 504516.

The detection and attribution of climate change in the observed record plays a central role in synthesizing our knowledge of the climate system. Unfortunately, the traditional method for detecting and attributing changes due to multiple forcings requires large numbers of general circulation model (GCM) simulations incorporating different initial conditions and forcing scenarios and these have only been performed with a small number of GCMs. This paper presents an extension to the fingerprinting technique which permits the inclusion of GCMs in the multi-signal analysis of surface temperature even when the required families of ensembles have not been generated. This is achieved by fitting a series of energy balance models (EBMs) to the GCM output in order to estimate the temporal response patterns to the various forcings.

This methodology is applied to the very large Challenge ensemble of 62 simulations of historical climate conducted with the NCAR CCSM 1.4 GCM, as well as some simulations from other GCMs. Considerable uncertainty exists in the estimates of the parameters in fitted EBMs. Nevertheless, temporal response patterns from these EBMs are more reliable and the combined EBM time series closely mimics the GCM in the context of transient forcing. In particular, detection and attribution results from this technique appear self-consistent and consistent with results from other methods provided that all major forcings are included in the analysis.

Using this technique on the Challenge ensemble, the estimated responses to changes in greenhouse gases, tropospheric sulphate aerosols, and stratospheric volcanic aerosols are all detected in the observed record, but only the response to the tropospheric sulphate aerosols is consistent with the observed record without a scaling of the amplitude. The estimated GCM response to SOL forcing is inconsistent with the observations. The result is that the temperature difference of the 1995-2004 decade relative to the 1940-1949 decade can be attributed to greenhouse gas emissions, with a partially offsetting cooling from sulphate emissions and little contribution from natural sources.

The results support the viability of the new methodology as an extension to current analysis tools for the detection and attribution of climate change which will allow the inclusion of many more GCMs. Shortcomings remain, however, and so it should not be considered a replacement to traditional techniques.

Full Article: http://www.atm.ox.ac.uk/user/stoned/papers/StoneDA_AllenMR_etalii_2007.pdf

Last Updated: 2007-02-27

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