Estimating uncertainties in global and North American regional climate change projections using a multi-thousand member climate model ensemble: Evaluation of the control simulations

Information on the uncertainties in projections of future climate change is vital for their effective use across a wide range of applications. A multi-thousand member perturbed-physics ensemble of climate model simulations is being used to better estimate model uncertainties in climate change projections for the globe, North American region and sub-regions. Ensemble members have been generated by the distributed computing project climateprediction.net at the University of Oxford, where thousands of simulations have been run on PCs across the globe, each running a different version of the Hadley Centre HadCM3L global coupled ocean-atmosphere climate model with perturbed physics parameterizations.

The HadCM3L model has horizontal resolution of 3.75 degrees longitude by 2.5 degrees latitude with 19 vertical layers in the atmosphere and 20 vertical layers in the ocean. A 30 minute dynamical integration time step is used with physics parameterization run every 3 hours. Transient climate change simulations are available from 1921 to 2080 along with matching control simulations that use flux adjustments to maintain stable climates. For the period 1921 to 2000, the model is forced by observed changes in both anthropogenic and natural climate forcing factors, including changes in greenhouse gases and aerosols, and changes in solar irradiance and volcanic aerosols. For the period 2001 to 2080, the model is forced by a range of future solar and volcanic forcing scenarios as well as projected changes in anthropogenic greenhouse gases and aerosols according to the IPCC SRES A1B emission scenario, a mid-range scenario. Model physics parameters are varied within their current range of uncertainty for each forcing scenario, providing an ensemble of more than 6,500 climate simulations. Output variables are available in the form of globally gridded 10-year means and time series monthly means for the globe and 51 separate regions (including six regions covering North America) over the full time period, 1921-2080.

An assessment of control simulation performance for mean climate and variability over the globe and North American regions will be presented. Preliminary transient simulation ensemble results also will be presented.