rcp45 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.

                4.1 rcp45 (4.1 RCP4.5): Future projection (2006-2100) forced by RCP4.5. RCP4.5 is a representative concentration pathway which approximately results in a radiative  forcing of 4.5 W m-2 at year 2100, relative to pre-industrial conditions. RCPs are time-dependent, consistent projections of emissions and concentrations  of radiatively active gases and particles.

                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.