To run a case with the pre-industrial (1850) emissions and other forcing kept to present day (2000):1. use the FC5 compset to create a new_case (the FC5 compset will set all the forcing/boundary conditions to present values)2. invoke cesm_setup3. edit the user_nl_cam to replace the 2000 values by the 1850 values.It means that you add the following lines to your user_nl_cam: ext_frc_specifier = 'SO2 -> /glade/p/cesmdata/cseg/inputdata/atm/cam/chem/trop_mozart_aero/emis/ar5_mam3_so2_elev_1850_c090726.nc',
'bc_a1 -> /glade/p/cesmdata/cseg/inputdata/atm/cam/chem/trop_mozart_aero/emis/ar5_mam3_bc_elev_1850_c090726.nc',
'num_a1 -> /glade/p/cesmdata/cseg/inputdata/atm/cam/chem/trop_mozart_aero/emis/ar5_mam3_num_a1_elev_1850_c090726.nc',
'num_a2 -> /glade/p/cesmdata/cseg/inputdata/atm/cam/chem/trop_mozart_aero/emis/ar5_mam3_num_a2_elev_1850_c090726.nc',
'pom_a1 -> /glade/p/cesmdata/cseg/inputdata/atm/cam/chem/trop_mozart_aero/emis/ar5_mam3_oc_elev_1850_c090726.nc',
'so4_a1 -> /glade/p/cesmdata/cseg/inputdata/atm/cam/chem/trop_mozart_aero/emis/ar5_mam3_so4_a1_elev_1850_c090726.nc',
'so4_a2 -> /glade/p/cesmdata/cseg/inputdata/atm/cam/chem/trop_mozart_aero/emis/ar5_mam3_so4_a2_elev_1850_c090726.nc'
ext_frc_type = 'CYCLICAL'
srf_emis_specifier = 'DMS -> /glade/p/cesmdata/cseg/inputdata/atm/cam/chem/trop_mozart_aero/emis/aerocom_mam3_dms_surf_2000_c090129.nc',
'SO2 -> /glade/p/cesmdata/cseg/inputdata/atm/cam/chem/trop_mozart_aero/emis/ar5_mam3_so2_surf_1850_c090726.nc',
'SOAG -> /glade/p/cesmdata/cseg/inputdata/atm/cam/chem/trop_mozart_aero/emis/ar5_mam3_soag_1.5_surf_1850_c100217.nc',
'bc_a1 -> /glade/p/cesmdata/cseg/inputdata/atm/cam/chem/trop_mozart_aero/emis/ar5_mam3_bc_surf_1850_c090726.nc',
'num_a1 -> /glade/p/cesmdata/cseg/inputdata/atm/cam/chem/trop_mozart_aero/emis/ar5_mam3_num_a1_surf_1850_c090726.nc',
'num_a2 -> /glade/p/cesmdata/cseg/inputdata/atm/cam/chem/trop_mozart_aero/emis/ar5_mam3_num_a2_surf_1850_c090726.nc',
'pom_a1 -> /glade/p/cesmdata/cseg/inputdata/atm/cam/chem/trop_mozart_aero/emis/ar5_mam3_oc_surf_1850_c090726.nc',
'so4_a1 -> /glade/p/cesmdata/cseg/inputdata/atm/cam/chem/trop_mozart_aero/emis/ar5_mam3_so4_a1_surf_1850_c090726.nc',
'so4_a2 -> /glade/p/cesmdata/cseg/inputdata/atm/cam/chem/trop_mozart_aero/emis/ar5_mam3_so4_a2_surf_1850_c090726.nc'
srf_emis_type = 'CYCLICAL'