diff --git a/earthdiagnostics/cmorizer.py b/earthdiagnostics/cmorizer.py
index cc254ead6a10a592d691db88ec1210d9d509f281..6cb10a3dd1d8c9aa50a7c14938a51a0354fb2be0 100644
--- a/earthdiagnostics/cmorizer.py
+++ b/earthdiagnostics/cmorizer.py
@@ -318,7 +318,25 @@ class Cmorizer(object):
                         options="-O", input=filename, output=temp
                     )
                     shutil.move(temp, filename)
-            Utils.cdo().mergetime(input=files, output=merged)
+            cmorize_vars = set()
+            var_manager = self.config.var_manager
+            for filename in files:
+                handler = Utils.open_cdf(filename)
+                for variable in handler.variables.keys():
+
+                    _, var_cmor = var_manager.get_variable_and_alias(
+                        variable, silent=True,
+                    )
+                    if self.cmor.cmorize(var_cmor):
+                        cmorize_vars.add(variable)
+                handler.close()
+            if not cmorize_vars:
+                continue
+            var_str = ",".join([str(var) for var in cmorize_vars])
+            Utils.cdo().mergetime(
+                input=[f"-selvar,{var_str} {filepath}" for filepath in files],
+                output=merged
+            )
             for filename in files:
                 self._remove(filename)
             tar_startdate = (
diff --git a/test/integration/test_cmorizer.py b/test/integration/test_cmorizer.py
index 14ee5db2b184f6566c831845a678eb86924ec22c..29fab22bb4457edb912b0b75fc569ca04f6d2fa6 100644
--- a/test/integration/test_cmorizer.py
+++ b/test/integration/test_cmorizer.py
@@ -21,7 +21,7 @@ import calendar
 class TestCmorizer(TestCase):
     """Tests for Cmorizer class"""
 
-    def _get_variable_and_alias(self, variable):
+    def _get_variable_and_alias(self, variable, silent=False):
         mock_alias = Mock()
         mock_alias.basin = None
         mock_alias.grid = None
@@ -349,22 +349,26 @@ class TestCmorizer(TestCase):
                         log.Log.WARNING: warnings,
                     }
                 ):
-                    if value:
-                        self.assertTrue(
-                            [
-                                record
-                                for record in cmd.records
-                                if record.levelno == level
-                            ]
-                        )
-                    else:
-                        self.assertFalse(
-                            [
-                                record
-                                for record in cmd.records
-                                if record.levelno == level
-                            ]
-                        )
+                    try:
+                        if value:
+                            self.assertTrue(
+                                [
+                                    record
+                                    for record in cmd.records
+                                    if record.levelno == level
+                                ]
+                            )
+                        else:
+                            self.assertFalse(
+                                [
+                                    record
+                                    for record in cmd.records
+                                    if record.levelno == level
+                                ]
+                            )
+                    except AssertionError:
+                        print(cmd.records)
+                        raise
         else:
             cmorizer = Cmorizer(self.data_manager, "19900101", 0)
             if ocean: