Best available estimates of forcing histories have recently been compiled, for the natural (orbital, total solar irradiance, volcanic aerosols) and anthropogenic forcings (greenhouse gas, sulphate aerosols, land cover changes, and tropospheric and stratospheric ozone). These are being/will be used to force two state-of-the-art coupled climate models. Both models already have at least millennial-length control integrations. Partner 3 (METO) will run HadCM3 from AD 1500 to 2000 under natural forcings, and then repeat the period from AD 1750 onwards with both natural and anthropogenic (all) forcings. These simulations will be funded using partner 3's own resources and will be undertaken during 2002 and completed by the start date of the proposed SOAP project. Partners 4 and 5 are currently undertaking simulations using ECHAM4/HOPE with funding from a current (nationally-funded) project. These are, effectively, natural forcings for AD 1000 to 1750 and all forcings for AD 1750 to 2000, and will be provided for use in the proposed SOAP project. These will be augmented by an extension of the natural forcing simulation from AD 1750 to 2000, to be undertaken by partner 4 (FUB) with funding from the proposed project. As far as logistics and different model formulations allow, the two models will perform identical experiments. Appropriate data and diagnostics will be converted to netCDF file format and transferred to the web-based project data bank for dissemination within the project (and for public dissemination at the end of the project).
Comparison of forced and control simulations (and also intercomparison of the two models) will be done using a range of statistical approaches, tailored to specific questions. Comparisons will be done on the means and variance of temperature, precipitation and indices (such as ENSO, NAO, etc.), and on statistics (quantiles, return periods) linked to extreme events (hot/cold summers, droughts). Comparisons will be done using the whole of each simulation, but also as a function of time to identify periods and variables when the forced simulations are significantly different from the control simulations (this will provide input to WP4, to look at proxy data during these identified periods). Comparisons will also take place over a range of space and time scales. This part of the study will answer the question: "how does external forcing alter the climate and its variability?". The natural simulations will be used to estimate the contribution of natural forcing to climate variability while the all experiments will be used to compare the simulations with proxy data in order to evaluate the veracity of the simulations. There will be a specific focus on diagnosing the simulated response to external forcings, taking into account the seasonality of moisture, circulation and temperature responses, and time lags in maximum response (especially important for solar forcing with its multiple time scales of variability).
This climate simulation and model analysis/intercomparison workpackage will be led by partner 3 (METO), with FUB undertaking a new simulation specifically for the SOAP project, while METO and GKSS will contribute their simulations without cost to the project. Partners 3, 4 and 5 will take part in the analysis and intercomparison of the model output.