Quantifying Uncertainties in Global and North American Regional Climate Change Projections using the Climateprediction.net Multi-Thousand Member Global Climate Model Perturbed Physics Ensemble

Thursday, 18 December 2014
Derek H Rosendahl, South Central Climate Science Center, Norman, OK, United States and David J Karoly, University of Melbourne, University of Melbourne, Australia
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 global climate model simulations is being used to better estimate model uncertainties in climate change projections for the globe and North America. 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 coupled atmosphere-ocean general circulation model (CMIP3 version) with perturbed physics parameters. Results from this perturbed physics ensemble will be compared to results from the CMIP3 and CMIP5 multi-model ensembles for global and North American regional temperature and precipitation variability and change across the 20th and 21st centuries. It will be shown that the uncertainty in the perturbed physics ensemble can exceed that of the multi-model ensemble.   

The HadCM3L model has horizontal resolution of 2.5° latitude by 3.75° longitude 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 1,700 transient and 1,200 control simulations.