The HadCM3L model has horizontal resolution of 3.75 degree longitude by 2.5 degree 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 6,000 transient (3,000 control) 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.
The simulated 20th century climate variations are compared with observed climate variations to assess their performance. Projections of climate change over the 21st century are obtained by weighting the different ensemble members by their goodness-of-fit to the 20th century observed changes, discarding those members considered to have inadequate simulations. This constrained data is used to estimate probability distributions of future mean climate and variability which can provide insight into sources of model uncertainties in projected future climate change for the globe and North American region.