'historical' is an experiment of the CMIP5 - Coupled Model Intercomparison Project Phase 5 (https://pcmdi.llnl.gov/mips/cmip5). CMIP5 is meant to provide a framework for coordinated climate change experiments for the next five years and thus includes simulations for assessment in the AR5 as well as others that extend beyond the AR5.

                3.2 historical (3.2 Historical): Simulation of recent past (1850 to 2005). Impose changing conditions (consistent with observations).

                Experiment design is described in detail in https://pcmdi.llnl.gov/mips/cmip5/experiment_design.html and the list of output variables and their temporal resolutions are given in https://pcmdi.llnl.gov/mips/cmip5/datadescription.html .
                The output is stored in netCDF format as time series per variable in model grid spatial resolution. For more information on the Earth System model and the simulation please refer to the CIM repository.

                There are five component models: atmosphere, surface land, ocean, sea ice and surface wave models.