Quantifying Uncertainty in the Attribution of Recent Climate Change (quarcc)

One of the objectives of the QUARCC project is to investigate the robustness of recent reports of an anthropogenic innuence on global climate through the application of a consistent optimal detection and attribution methodology to a wider range of alternative climate change mechanisms and a wider range of model predictions and observational data sources than have been addressed to date. The activities in the rst project year focused on this area by applying an optimal ngerprint technique to the newest Hamburg climate model experiments and to a few diierent climate variables which have been discussed as indicators of climate change. In the past optimal ngerprint methods have been mainly used for the detection and attribution of anthropogenically caused climate change in observational records of near-surface temperature. Mostly, these techniques have been applied to decadal, annual or seasonal averages and only more recently, other geophysical or statistical parameters than surface temperature are included in detection studies. If it is possible to positively detect and attribute climate change (avoiding the double negation of hypothesis testing here) in additional parameters we could have higher conndence in claims of human activities innuencing climate. Ideally, these parameters should be orthogonal to the global temperature patterns to provide additional information. Here, we therefore consider precipitation and diurnal temperature range (DTR) in addition to near-surface temperature. Furthermore , we include a formal representation of the annual cycle of the parameters in question in the ngerprint study instead of performing separate analyses for the seasons. One approach to assess the innuence of uncertainties in the estimation of signal patterns and natural variability is through model-model intercomparison. For this purpose we used the most recent climate change experiments performed with the ECHAM4/OPYC3 climate model at the Max-Planck-Institute (Roeckner et al., 1998; Bengtsson et al., 1998). They include, for the rst time, an experiment with the full interactive computation of the direct and indirect eeect of sulfate aerosols and tropospheric ozone which will also beneet the uncertainty assessment of the role of diierent forcing mechanisms for the attribution of climate change. The ECHAM4/OPYC3 experiments used here include a greenhouse gas only run (GHG), one run with greenhouse gases plus the direct eeect of sulfate aerosols (GSD and the above mentioned experiment with greenhouse gases and direct/indirect sulfate aerosols and tropospheric ozone (GSDIO). The forcings in these transient runs starting in 1860 were speciied from observations until 1990 and according to …