historicalExt 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.
7.4 historicalExt (7.4 Historical Extension) - Version 1: Extend the CMIP5 historical runs to the near-present (as we have for AMIP), rather than ending them in 2005. Simulations extended to at least the end of 2012 using some estimate of recent and future forcing. Groups are free to use whatever concentrations, solar forcing, SO2 emissions etc. they want to use in extending these runs. It is recommended that if an ensemble of "all-forcings" historical simulations have been run, then *each* member of the ensemble should be carried to the end of 2012. If some other forcing is used or if the run is an RCP run that is truncated after a few years, then the run should be considered a "historical extension" experiment with its output placed in a directory named historicalExt. For these historicalExt experiments, the ensemble member (designated by the "rip" value appearing in the filename and recorded as netCDF global attributes) will be identical to the historical run it extends.
List of output variables: https://pcmdi.llnl.gov/mips/cmip5/datadescription.html
Output: time series per variable in model grid spatial resolution in netCDF format
Earth System model and the simulation information: CIM repository
Entry name/title of data are specified according to the Data Reference Syntax ( https://pcmdi.llnl.gov/mips/cmip5/docs/cmip5_data_reference_syntax.pdf ) as activity/product/institute/model/experiment/frequency/modeling realm/MIP table/ensemble member/version number/variable name/CMOR filename.nc .