diff --git a/exp/test_cases/held_suarez/held_suarez_test_case_single.py b/exp/test_cases/held_suarez/held_suarez_test_case_single.py
new file mode 100644
index 000000000..d815ce4ad
--- /dev/null
+++ b/exp/test_cases/held_suarez/held_suarez_test_case_single.py
@@ -0,0 +1,110 @@
+import numpy as np
+
+from isca import DryCodeBase, DiagTable, Experiment, Namelist, GFDL_BASE
+
+NCORES = 16
+RESOLUTION = 'T42', 25  # T42 horizontal resolution, 25 levels in pressure
+
+# a CodeBase can be a directory on the computer,
+# useful for iterative development
+cb = DryCodeBase.from_directory(GFDL_BASE)
+
+# or it can point to a specific git repo and commit id.
+# This method should ensure future, independent, reproducibility of results.
+# cb = DryCodeBase.from_repo(repo='https://github.com/isca/isca', commit='isca1.1')
+
+# compilation depends on computer specific settings.  The $GFDL_ENV
+# environment variable is used to determine which `$GFDL_BASE/src/extra/env` file
+# is used to load the correct compilers.  The env file is always loaded from
+# $GFDL_BASE and not the checked out git repo.
+cb.use_single_precision()
+
+cb.compile()  # compile the source code to working directory $GFDL_WORK/codebase
+
+# create an Experiment object to handle the configuration of model parameters
+# and output diagnostics
+
+exp_name = 'held_suarez_default_single_precision'
+exp = Experiment(exp_name, codebase=cb)
+
+#Tell model how to write diagnostics
+diag = DiagTable()
+diag.add_file('atmos_monthly', 30, 'days', time_units='days')
+
+#Tell model which diagnostics to write
+diag.add_field('dynamics', 'ps', time_avg=True)
+diag.add_field('dynamics', 'bk')
+diag.add_field('dynamics', 'pk')
+diag.add_field('dynamics', 'ucomp', time_avg=True)
+diag.add_field('dynamics', 'vcomp', time_avg=True)
+diag.add_field('dynamics', 'temp', time_avg=True)
+diag.add_field('dynamics', 'vor', time_avg=True)
+diag.add_field('dynamics', 'div', time_avg=True)
+
+exp.diag_table = diag
+
+# define namelist values as python dictionary
+# wrapped as a namelist object.
+namelist = Namelist({
+    'main_nml': {
+        'dt_atmos': 600,
+        'days': 30,
+        'calendar': 'thirty_day',
+        'current_date': [2000,1,1,0,0,0]
+    },
+
+    'atmosphere_nml': {
+        'idealized_moist_model': False  # False for Newtonian Cooling.  True for Isca/Frierson
+    },
+
+    'spectral_dynamics_nml': {
+        'damping_order'           : 4,                      # default: 2
+        'water_correction_limit'  : 200.e2,                 # default: 0
+        'reference_sea_level_press': 1.0e5,                  # default: 101325
+        'valid_range_t'           : [100., 800.],           # default: (100, 500)
+        'initial_sphum'           : 0.0,                  # default: 0
+        'vert_coord_option'       : 'uneven_sigma',         # default: 'even_sigma'
+        'scale_heights': 6.0,
+        'exponent': 7.5,
+        'surf_res': 0.5
+    },
+
+    # configure the relaxation profile
+    'hs_forcing_nml': {
+        't_zero': 315.,    # temperature at reference pressure at equator (default 315K)
+        't_strat': 200.,   # stratosphere temperature (default 200K)
+        'delh': 60.,       # equator-pole temp gradient (default 60K)
+        'delv': 10.,       # lapse rate (default 10K)
+        'eps': 0.,         # stratospheric latitudinal variation (default 0K)
+        'sigma_b': 0.7,    # boundary layer friction height (default p/ps = sigma = 0.7)
+
+        # negative sign is a flag indicating that the units are days
+        'ka':   -40.,      # Constant Newtonian cooling timescale (default 40 days)
+        'ks':    -4.,      # Boundary layer dependent cooling timescale (default 4 days)
+        'kf':   -1.,       # BL momentum frictional timescale (default 1 days)
+
+        'do_conserve_energy':   True,  # convert dissipated momentum into heat (default True)
+    },
+
+    'diag_manager_nml': {
+        'mix_snapshot_average_fields': False
+    },
+
+    'fms_nml': {
+        'domains_stack_size': 600000                        # default: 0
+    },
+
+    'fms_io_nml': {
+        'threading_write': 'single',                         # default: multi
+        'fileset_write': 'single',                           # default: multi
+    }
+})
+
+exp.namelist = namelist
+exp.set_resolution(*RESOLUTION)
+
+#Lets do a run!
+if __name__ == '__main__':
+    exp.run(1, num_cores=NCORES, use_restart=False)
+    for i in range(2, 13):
+        exp.run(i, num_cores=NCORES)  # use the restart i-1 by default
\ No newline at end of file
diff --git a/src/atmos_param/cloud_simple/cloud_cover_diags.F90 b/src/atmos_param/cloud_simple/cloud_cover_diags.F90
index aea5b337d..197db9639 100644
--- a/src/atmos_param/cloud_simple/cloud_cover_diags.F90
+++ b/src/atmos_param/cloud_simple/cloud_cover_diags.F90
@@ -7,7 +7,7 @@ module cloud_cover_diags_mod
 #endif
 
   use           fms_mod, only: stdlog, FATAL, WARNING, NOTE, error_mesg, &
-                               uppercase, check_nml_error
+                               uppercase, check_nml_error, file_exist
   use  time_manager_mod, only: time_type
   use  diag_manager_mod, only: register_diag_field, send_data
 
diff --git a/src/atmos_param/cloud_simple/cloud_simple.F90 b/src/atmos_param/cloud_simple/cloud_simple.F90
index 2e65dfaa6..6aa521726 100644
--- a/src/atmos_param/cloud_simple/cloud_simple.F90
+++ b/src/atmos_param/cloud_simple/cloud_simple.F90
@@ -7,7 +7,7 @@ module cloud_simple_mod
 #endif
 
   use                fms_mod, only: stdlog, FATAL, WARNING, NOTE, error_mesg, &
-                                    uppercase, check_nml_error
+                                    uppercase, check_nml_error, file_exist
   use       time_manager_mod, only: time_type
   use     sat_vapor_pres_mod, only: compute_qs, lookup_es
   use       diag_manager_mod, only: register_diag_field, send_data
diff --git a/src/atmos_param/cloud_simple/large_scale_cloud.F90 b/src/atmos_param/cloud_simple/large_scale_cloud.F90
index c26a78f4b..7e13c13c9 100644
--- a/src/atmos_param/cloud_simple/large_scale_cloud.F90
+++ b/src/atmos_param/cloud_simple/large_scale_cloud.F90
@@ -7,7 +7,7 @@ module large_scale_cloud_mod
 #endif
 
   use            fms_mod, only: stdlog, FATAL, WARNING, NOTE, error_mesg, &
-                                uppercase, check_nml_error
+                                uppercase, check_nml_error, file_exist
   use   time_manager_mod, only: time_type
   use sat_vapor_pres_mod, only: compute_qs, lookup_es
   use   diag_manager_mod, only: register_diag_field, send_data
diff --git a/src/atmos_param/cloud_simple/lcl.F90 b/src/atmos_param/cloud_simple/lcl.F90
index 7205bed09..0d8260789 100644
--- a/src/atmos_param/cloud_simple/lcl.F90
+++ b/src/atmos_param/cloud_simple/lcl.F90
@@ -38,17 +38,17 @@ function lcl(p,T,rh,rhl,rhs,return_ldl,return_min_lcl_ldl)
    implicit none
 
    ! In
-   double precision, intent(in) :: p, T
-   double precision, intent(in), optional :: rh, rhl, rhs
+   real, intent(in) :: p, T
+   real, intent(in), optional :: rh, rhl, rhs
    logical, intent(in), optional :: return_ldl, return_min_lcl_ldl
 
    ! Out
-   double precision :: lcl
+   real :: lcl
 
    logical :: liquid2, solid2
    integer(kind=4) :: error
 
-   double precision :: Ttrip, ptrip, E0v, E0s, ggr, rgasa, &
+   real :: Ttrip, ptrip, E0v, E0s, ggr, rgasa, &
       rgasv, cva, cvv, cvl, cvs, cpa, cpv, al, bl, cl, as, bs, cs, &
       pv, qv, cpm, rgasm, rh2, rhl2, rhs2, ldl
    integer :: rh_counter
@@ -167,8 +167,8 @@ function pvstarl(T)
 
         implicit none
 
-        double precision :: T        ! In
-        double precision :: pvstarl  ! Out
+        real :: T        ! In
+        real :: pvstarl  ! Out
   
         pvstarl = ptrip * (T/Ttrip)**((cpv-cvl)/rgasv) * &
           exp( (E0v - (cvv-cvl)*Ttrip) / rgasv * (1./Ttrip - 1./T) )
@@ -180,8 +180,8 @@ function pvstars(T)
          
         implicit none
 
-        double precision :: T        ! In
-        double precision :: pvstars  ! Out
+        real :: T        ! In
+        real :: pvstars  ! Out
   
         pvstars = ptrip * (T/Ttrip)**((cpv-cvs)/rgasv) * &
           exp( (E0v + E0s - (cvv-cvs)*Ttrip) / rgasv * (1./Ttrip - 1./T) )
@@ -234,7 +234,7 @@ function bisect ( xx, nb, ner, l )
 !
 !  Parameters:
 !
-!    Input, double precision :: XX, the argument.
+!    Input, real :: XX, the argument.
 !
 !    Input, integer ( kind = 4 ) NB, indicates the branch of the W function.
 !    0, the upper branch;
@@ -248,15 +248,15 @@ function bisect ( xx, nb, ner, l )
 !    1, XX represents the offset of the argument from -exp(-1).
 !    not 1, XX is the actual argument.
 !
-!    Output, double precision :: BISECT, the value of W(X), as determined
+!    Output, real :: BISECT, the value of W(X), as determined
 !
   implicit none
 
-  double precision :: bisect
-!  double precision :: crude
-  double precision :: d
-  double precision :: f
-  double precision :: fd
+  real :: bisect
+!  real :: crude
+  real :: d
+  real :: f
+  real :: fd
   integer ( kind = 4 ) i
   integer ( kind = 4 ) l
   integer ( kind = 4 ) n0
@@ -264,12 +264,12 @@ function bisect ( xx, nb, ner, l )
   integer ( kind = 4 ) nb
   integer ( kind = 4 ), save :: nbits = 0
   integer ( kind = 4 ) ner
-  double precision :: r
-  double precision :: test
-  double precision :: tol
-  double precision :: u
-  double precision :: x
-  double precision :: xx
+  real :: r
+  real :: test
+  real :: tol
+  real :: u
+  real :: x
+  real :: xx
 
   bisect = 0.0D+00
   ner = 0
@@ -414,34 +414,34 @@ function crude ( xx, nb )
 !
 !  Parameters:
 !
-!    Input, double precision :: XX, the argument.
+!    Input, real :: XX, the argument.
 !
 !    Input, integer ( kind = 4 ) NB, indicates the desired branch.
 !    * 0, the upper branch;
 !    * nonzero, the lower branch.
 !
-!    Output, double precision :: CRUDE, the crude approximation to W at XX.
+!    Output, real :: CRUDE, the crude approximation to W at XX.
 !
   implicit none
 
-  double precision :: an2
-  double precision :: c13
-  double precision :: crude
-  double precision :: em
-  double precision :: em2
-  double precision :: em9
-  double precision :: eta
+  real :: an2
+  real :: c13
+  real :: crude
+  real :: em
+  real :: em2
+  real :: em9
+  real :: eta
   integer ( kind = 4 ) init
   integer ( kind = 4 ) nb
-  double precision :: reta
-  double precision :: s2
-  double precision :: s21
-  double precision :: s22
-  double precision :: s23
-  double precision :: t
-  double precision :: ts
-  double precision :: xx
-  double precision :: zl
+  real :: reta
+  real :: s2
+  real :: s21
+  real :: s22
+  real :: s23
+  real :: t
+  real :: ts
+  real :: xx
+  real :: zl
 
   save c13
   save em
@@ -525,7 +525,7 @@ subroutine nbits_compute ( nbits )
 !    function should be calculated.
 !
 !    Most machines use a 24-bit matissa for single precision and
-!    53-56 bits for double precision ::. The IEEE standard is 53
+!    53-56 bits for real ::. The IEEE standard is 53
 !    bits. The Fujitsu VP2200 uses 56 bits. Long word length
 !    machines vary, e.g., the Cray X/MP has a 48-bit mantissa for
 !    single precision.
@@ -559,10 +559,10 @@ subroutine nbits_compute ( nbits )
 !
   implicit none
 
-  double precision :: b
+  real :: b
   integer ( kind = 4 ) i
   integer ( kind = 4 ) nbits
-  double precision :: v
+  real :: v
 
   nbits = 0
 
@@ -701,7 +701,7 @@ function wapr ( x, nb, nerror, l )
 !
 !  Parameters:
 !
-!    Input, double precision :: X, the argument.
+!    Input, real :: X, the argument.
 !
 !    Input, integer ( kind = 4 ) NB, indicates the desired branch.
 !    * 0, the upper branch;
@@ -715,23 +715,23 @@ function wapr ( x, nb, nerror, l )
 !    * 1, X is actually the offset from -(exp-1), so compute W(X-exp(-1)).
 !    * not 1, X is the argument; compute W(X);
 !
-!    Output, double precision :: WAPR, the approximate value of W(X).
+!    Output, real :: WAPR, the approximate value of W(X).
 !
   implicit none
 
-  double precision :: an2
-  double precision :: an3
-  double precision :: an4
-  double precision :: an5
-  double precision :: an6
-  double precision :: c13
-  double precision :: c23
-  double precision :: d12
-  double precision :: delx
-  double precision :: em
-  double precision :: em2
-  double precision :: em9
-  double precision :: eta
+  real :: an2
+  real :: an3
+  real :: an4
+  real :: an5
+  real :: an6
+  real :: c13
+  real :: c23
+  real :: d12
+  real :: delx
+  real :: em
+  real :: em2
+  real :: em9
+  real :: eta
   integer ( kind = 4 ) i
   integer ( kind = 4 ) init
   integer ( kind = 4 ) l
@@ -740,24 +740,24 @@ function wapr ( x, nb, nerror, l )
   integer ( kind = 4 ) nbits
   integer ( kind = 4 ) nerror
   integer ( kind = 4 ) niter
-  double precision :: reta
-  double precision :: s2
-  double precision :: s21
-  double precision :: s22
-  double precision :: s23
-  double precision :: t
-  double precision :: tb
-  double precision :: tb2
-  double precision :: temp
-  double precision :: temp2
-  double precision :: ts
-  double precision :: wapr
-  double precision :: x
-  double precision :: x0
-  double precision :: x1
-  double precision :: xx
-  double precision :: zl
-  double precision :: zn
+  real :: reta
+  real :: s2
+  real :: s21
+  real :: s22
+  real :: s23
+  real :: t
+  real :: tb
+  real :: tb2
+  real :: temp
+  real :: temp2
+  real :: ts
+  real :: wapr
+  real :: x
+  real :: x0
+  real :: x1
+  real :: xx
+  real :: zl
+  real :: zn
 
   save an3
   save an4
diff --git a/src/atmos_param/cloud_simple/marine_strat_cloud.F90 b/src/atmos_param/cloud_simple/marine_strat_cloud.F90
index 007af2e5f..de65f6516 100644
--- a/src/atmos_param/cloud_simple/marine_strat_cloud.F90
+++ b/src/atmos_param/cloud_simple/marine_strat_cloud.F90
@@ -7,7 +7,7 @@ module marine_strat_cloud_mod
 #endif
 
   use             fms_mod, only: stdlog, FATAL, WARNING, NOTE, error_mesg, &
-                                 uppercase, check_nml_error
+                                 uppercase, check_nml_error, file_exist
   use    time_manager_mod, only: time_type
   use  sat_vapor_pres_mod, only: compute_qs, lookup_es
   use    diag_manager_mod, only: register_diag_field, send_data
diff --git a/src/extra/python/isca/codebase.py b/src/extra/python/isca/codebase.py
index ada901b27..6b86872e0 100644
--- a/src/extra/python/isca/codebase.py
+++ b/src/extra/python/isca/codebase.py
@@ -120,6 +120,8 @@ def __init__(self, repo=None, commit=None, directory=None, storedir=P(GFDL_WORK,
         # read path names from the default file
         self.path_names = []
         self.compile_flags = []  # users can append to this to add additional compiler options
+        self.precision_compile_flags = ['-DOVERLOAD_C8'] #Default is to use double precision. User can change to single precision using cb.use_single_precision() before compile step 
+        self.env_suffix = ''
 
     @property
     def code_is_available(self):
@@ -255,6 +257,7 @@ def compile(self, debug=False, optimisation=None):
         #     compile_flags.append('-O%d' % optimisation)
 
         compile_flags.extend(self.compile_flags)
+        compile_flags.extend(self.precision_compile_flags)        
         compile_flags_str = ' '.join(compile_flags)
 
         # get path_names from the directory
@@ -269,7 +272,7 @@ def compile(self, debug=False, optimisation=None):
             'srcdir': self.srcdir,
             'workdir': self.workdir,
             'compile_flags': compile_flags_str,
-            'env_source': env,
+            'env_source': env+self.env_suffix,
             'path_names': path_names_str,
             'executable_name': self.executable_name,
             'run_idb': debug,
@@ -282,6 +285,13 @@ def compile(self, debug=False, optimisation=None):
 
         self.log.info('Compilation complete.')
 
+    def use_single_precision(self):
+            self.log.info('Going to use single_precision')
+            self.precision_compile_flags = ['-DOVERLOAD_C4', '-DOVERLOAD_R4']
+            self.executable_name = self.executable_name.strip('.x')+'_single.x'
+            self.builddir = P(self.workdir, 'build', self.executable_name.split('.')[0])
+            self.env_suffix = '_single' #needs a seperate env file as flags are different
+
 
 
 class IscaCodeBase(CodeBase):
diff --git a/src/extra/python/isca/templates/compile.sh b/src/extra/python/isca/templates/compile.sh
index d20377492..759cd1f5f 100755
--- a/src/extra/python/isca/templates/compile.sh
+++ b/src/extra/python/isca/templates/compile.sh
@@ -53,13 +53,13 @@ if [ $debug == True ]; then
  echo "Compiling in debug mode"
 
 # execute mkmf to create makefile
-cppDefs="-Duse_libMPI -Duse_netCDF -Duse_LARGEFILE -DINTERNAL_FILE_NML -DOVERLOAD_C8 {{compile_flags}}"
+cppDefs="-Duse_libMPI -Duse_netCDF -Duse_LARGEFILE -DINTERNAL_FILE_NM {{compile_flags}}"
 $mkmf  -a $sourcedir -t $template_debug -p $executable -c "$cppDefs" $pathnames $sourcedir/shared/include $sourcedir/shared/mpp/include
 
 else
 
 # execute mkmf to create makefile
-cppDefs="-Duse_libMPI -Duse_netCDF -Duse_LARGEFILE -DINTERNAL_FILE_NML -DOVERLOAD_C8 {{compile_flags}}"
+cppDefs="-Duse_libMPI -Duse_netCDF -Duse_LARGEFILE -DINTERNAL_FILE_NM {{compile_flags}}"
 $mkmf  -a $sourcedir -t $template -p $executable -c "$cppDefs" $pathnames $sourcedir/shared/include $sourcedir/shared/mpp/include
 
 fi
diff --git a/src/extra/python/isca/templates/mkmf.template.maths2_single b/src/extra/python/isca/templates/mkmf.template.maths2_single
new file mode 100755
index 000000000..8b80014da
--- /dev/null
+++ b/src/extra/python/isca/templates/mkmf.template.maths2_single
@@ -0,0 +1,28 @@
+# template for the Intel fortran compiler
+# typical use with mkmf
+# mkmf -t template.ifc -c"-Duse_libMPI -Duse_netCDF" path_names /usr/local/include
+CPPFLAGS = `nc-config --cflags`
+NETCDF_LIBS = `nc-config --libs`
+
+# FFLAGS:
+#  -fpp: Use the fortran preprocessor
+#  -stack_temps:  Put temporary runtime arrays on the stack, not heap.
+#  -safe_cray_ptr: Cray pointers don't alias other variables.
+#  -ftz: Denormal numbers are flushed to zero.
+#  -assume byterecl: Specifies the units for the OPEN statement as bytes.
+#  -shared-intel:  Load intel libraries dynamically
+#  -i4: 4 byte integers
+#  -r8: 8 byte reals
+#  -g: Generate symbolic debugging info in code
+#  -O2: Level 2 speed optimisations
+#  -diag-disable 6843:
+#       This suppresses the warning: `warning #6843: A dummy argument with an explicit INTENT(OUT) declaration is not given an explicit value.` of which
+#       there are a lot of instances in the GFDL codebase.
+FFLAGS = $(CPPFLAGS) -fpp -stack_temps -safe_cray_ptr -ftz -assume byterecl -shared-intel -i4 -g -O2 -diag-disable 6843 -mcmodel large
+#FFLAGS = $(CPPFLAGS) -fltconsistency -stack_temps -safe_cray_ptr -ftz -shared-intel -assume byterecl -g -O0 -i4 -r8 -check -warn -warn noerrors -debug variable_locations -inline_debug_info -traceback
+FC = $(F90)
+LD = $(F90) $(NETCDF_LIBS)
+#CC = mpicc
+
+LDFLAGS = -lnetcdff -lnetcdf -lmpi -shared-intel -lhdf5_hl -lhdf5 -lm -lz -lsz -lbz2 -lxml2 -lcurl
+CFLAGS = -D__IFC